Dr. Herman Pontzer: How We Really Burn Calories & Lose Weight
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The science and practice of enhancing human performance for sport, play, and life. Welcome to Perform. Perform.

I'm Dr. Andy Galpin. I'm a professor and scientist and the executive director of the Human Performance Center at Parker University. Today's guest is Dr. Herman Poncer. Herman has a PhD in biological anthropology and is currently a professor at Duke University in the area of evolutionary anthropology. In today's show, you're going to learn a lot about what Herman is probably most famous for, and that is how metabolism really works.

We talk at length and you'll learn a tremendous amount about how to properly think of energy expenditure, the role that exercise does

or maybe surprisingly doesn't have in things like energy expenditure, body weight, body composition, and overall health. He also does a wonderful job teaching about how energy expenditure changes with things like pregnancy and other things we don't typically think of as exercise or sport, but are highly relevant and incredibly interesting regarding how our metabolism and overall physiology works.

So there's a lot of practical tips here. There's a lot of just fascinating information. I know you'll enjoy it. I was thrilled to do it. I waited a long time to talk to Herman. So with that said, please enjoy today's episode with Dr. Herman Ponser. Dr. Herman Ponser, thank you for coming in today. It's fun to be here. It is a huge honor. I've been wanting to talk to you for a really long time, even before I had a podcast.

Your work is incredibly interesting. I'd actually like to start with exactly your work in the sense that your PhD is in anthropology from Harvard. Yep. But you probably are most, I'd say, notable for setting the world on fire a little bit with some interesting and controversial takes on metabolism, how the body burns fat, the role of physical exercise. You had a

a series of papers come out that, uh, I'd say put you on the map if that's a fair way to put it. So, uh,

What is it exactly that you do? Why is an anthropologist changing the way we think about metabolism? That's a great question. So, you know, as an anthropologist, I'm interested in how the human body works and how it got this way. Right. So sort of an evolutionary lens on the way the body functions. And so coming up through my training in undergrad and then graduate school, I never had any sort of public health or sort of, you know, obesity research sort of interests necessarily. Right.

I wanted to understand energy expenditure, though, because it's where the rubber hits the road. Any organism is, you can think of it as a strategy for turning energy into offspring. That's the game in life. And so from undergraduate up through graduate school, I was very interested in how the body brings energy in and burns it off. And

You start following your nose that way and you get into some interesting places because, you know, trying to understand how locomotion burns calories and how that relates to anatomy. That was my graduate work. Okay. And then when I kind of thought I understood that pretty well, I built like a put together a mathematical model for predicting the energy expenditure to go walk or run a mile depending on how your limb anatomy looks. Right.

I felt like I understood that pretty well. And I thought, okay, let's, let's, let's expand that. Let's think about a whole energy budget. How does a whole, you know, a chimp or a human or anything, how do we bring energy in and burn it off over 24 hours? The whole, the whole shoot and match. And, um, it turns out people hadn't really been doing a lot of measurements, uh, you know,

you know, of total energy expenditure, all energy burns for the whole day. In humans, outside of like Western context, we had data from the US or Europe. We didn't have data from traditional context, which is sort of more relevant for, you know, human evolutionary perspectives. We had no data on,

the other apes, that kind of thing. And so I started this whole, the last 20 years has been trying to measure energy expenditures in these contexts from an ecological evolutionary perspective. And then, you know, we wind up in some pretty interesting territory. Your first book, Burn, walks like through a lot of these things, but just as a starting place in the story here,

What is this deal with this hunter-gatherer group? What did we get wrong with the paleo diet? Like, give us the real quick overview there. So, you know, again, from an evolutionary perspective, how do we understand our body? Well, we are hunter-gatherers, right? Humans have been hunting and gathering since before we were humans, right? Two million years. And our species is only 300,000 years old. So that's, you know, we are a hunting and gathering species. That's the ecological context here.

And so if you want to understand how the body works, you know, California is fine and New York's fine, but more relevant would be a hunting and gathering context. And so luckily there are still a handful of communities that are still doing that, you know, and they're not, they're not like time machines of the past or anything like that, but they give us a sense of, okay, if you have this lifestyle and this ecological context, this is how the body would function.

They allow you to ask that question. And so nobody had measured energy expenditures in a hunter-gatherer group before. I had some colleagues that were working in northern Tanzania with a community called the Hadza. And so we went there and did this work. And so we...

use this technique called double-labeled water, which is this isotope tracking technique that's a really accurate measurement of how many... It actually measures how much carbon dioxide the body makes every day. So that tells you how many calories. It's over about a week or two-week period. So it's a really good look at how many calories you're burning. And we wrote those initial grants to go do this project because we wanted to document

how, like just the huge amount of calories that we were sure they were burning because they get more activity in a day than most Americans get in a week. Right, right, right. And so, and they were like, well, that's the way that humans used, everywhere used to live. Let's understand what that does to the body. It's the calorie expenditures are going to be huge. Nobody's measured it. It was exciting to go do this work, right? And so we go there to Northern Tanzania, 2009 and 2010, armed with, you know, isotopically enriched water and the whole kit.

And we do these measurements and we get back and get the data set back. And we're just completely shocked because, you know, actually, it turns out the total energy burned per day was no different than folks in the U.S., Europe, you know, people sitting at their desks all day. Like, what's going on? And so, you know, you have a choice there as a scientist. You have this model of how the world works.

It is totally crushed by the data, you know, and do you stick with the model or do you say, okay, these are the data. We're going to follow the data and say this is the observations. Obviously, you check and make sure you didn't make any silly mistakes. I think there's a little bit of a reckoning in your soul, right? You're like, oh, my God, our whole project is wrong. We've messed something up. That's exactly it. Right? And then you double and you triple and you standardize again and the data don't change. Yes, yes.

you know, and so what do you do? And so I thought, well, okay, here we go. I guess I'm going to talk about obesity now. So I said, cause that was this idea in public health. Of course, you still hear it. Oh, we're so sedentary now, which is true. And that's bad. That's true. And, um, and now we're not burning as many calories and that's why obesity is a problem. Well, that part turns out maybe not to be true. And so let's think about, you know, so I wrote the paper and, and, um,

You know, and then all of a sudden, like you say, I'm in this space talking to people like you. When you say energy expenditure. Yes. And you're saying things like these people who are hunter gatherers in various parts of Africa. And you've done that work in Tanzania and Kenya and you've sort of been all over.

And you say that that's not different than us sitting around all day. Yeah. What is energy expenditure? What are you actually talking about here? Yes. Good place to start. So you've got about 37 trillion cells in your body, give or take. Just a few. Yeah. Nobody's counting them, but you know, that's about that. And so every one of those cells is like a little factory, right? It's got a set of jobs it does. It brings resources in. It does its thing. And so every little factory is burning energy, right? And so all of that cumulatively is what we call your metabolic rate, right?

And we can think about all the energy that you burn over the course of a minute while you're on the treadmill. We can think about it while you're at rest, you know, for an hour. We can think about it over the course of 24 hours. And so the way that we usually measure it is over 24 hours. Actually, we measure it over a week or more, and then we take the average sort of per 24-hour period. And so that's your metabolic rate. And so it's all your systems all together. One of the things that people kind of misunderstand initially is,

is that they think, oh, well, your energy expenditure is all about how active you are. Even if you're active, most of your calories are being burnt on other things. Your immune system, your brain, you know, all the, you know. So anyway, so it's the full package. It's the whole, all the things that your bodies are doing. That's your metabolic rate that we're talking about. You know, not the per minute cost on a treadmill, not while you're just sleeping, but the whole thing. Right. So if you were to say,

All the calories you burn in a week. Some of them will be burned just staying alive. Yep. Right. We call that generally your basal metabolic rate or your resting metabolic rate, right? That's one of the components. Yeah. Then the calories that you burn working out, which is generally what, 5%, 10%?

It depends on how much you work out. So it can be 30% of your expenditure if you're active. Okay. So somewhere, basal metabolic rate is generally, what, 40, 50, 60%? Usually over half, a little over half. Yep. Yep. Then on top of that, you've got some additional calories you burn from...

twitching and fidgeting and that's what, another five or 10%? Well, it's hard to put numbers on that. So that's where it starts to break down because it's really hard to figure that out. This is where you've made your money, right? Yeah, I guess that's right. Yeah. And so, I mean, right now talking to you, I'm burning more calories than I was in the, you know, the Uber over here, chilled out, zoning out, right? And so we wouldn't call this physical activity, but my heart rate's higher, right? My sympathetic tone's higher, right? All those things. So I'm burning more calories just by being alert and attentive to you

A little bit of good stress happening, right? Hopefully. I think so. And so things like that burn calories too. And it's actually quite hard. One of the next things we want to try to do is to understand how that works. Because that's, I think, that's where the body can really juggle.

And can make space for somebody who's really physically active to still somehow have more or less the same energy expenditure per day as somebody who's sedentary because they're juggling these sort of, you know, these fungible things. Okay, tremendous. So when you say something like these hunter-gatherer groups, and Hudson is the one you worked on, it actually doesn't really matter. We're actually just thinking conceptually about how the body regulates energy. You have that one example, but...

We replicated other places. And yeah, it's a general concept. Right. So when you say they have the same energy expenditure as us, you're not talking about energy expenditure from physical activity.

Clearly that part is higher. Yes. That's the variable you knew. Yes. So is it their basal metabolic rate is higher or lower, or is it their other, this NEAT or some other factor? How is it that that total number, that total energy expenditure is the same? How are they manipulating their partitioning to hit the same final number? Yeah. So I don't think it's as simple as BMR, basal metabolic rates. I think it's the other parts of the awake day.

We know from—so here's where we have to move from those studies of folks like the Hadza and in those kind of ecological contexts to places, experimental setups where we can control things more and then we can have a better chance at getting exactly what's going on. So if we move this question about activity and expenditure into a lab here in the U.S. where we can control everything—

Here's what we know. If you look at athletes versus non-athletes, right, and you give them a stress, a psychosocial stress, the athlete will respond less. Their bump is smaller and it returns to baseline faster. So they've saved energy on that stress response. If you look at things like inflammation, inflammation is your immune system being overly active. It's going to cost, we don't know how many calories it costs, but it must cost something.

And you have less background inflammation if you are physically active than if you're not. If you look at things like testosterone levels or progesterone levels or estrogen, you know, depending on male or female athletes, endurance athletes especially will see reductions, not unhealthy, but, you know, moderations in levels of testosterone and that kind of thing. Those are anabolic steroid hormones. Those are building and burning energy. And there's less of it.

And so that's, we think, is how the body's kind of cobbling together. We think about it as an energy budget, right? How do you cobble together these pieces and keep the top line number, you know, kind of in the same place no matter what else is going on? Why would we want to, as a species, keep that top end number the same? Yeah, because, you know, an organism, from an evolutionary perspective, an organism should use every calorie it can without going over.

Right? If you aren't burning all the calories that are available to you, well, you're leaving money on the table. You could be burning those calories on reproduction, maintenance, repair, anything that was going to help you pass your genes on, which is what evolution cares about. So when times are good and you're not being super active, you should spend energy on other stuff.

When times are bad and you're going further to get your food and working really hard, well, now you don't want to just ramp up the total calories you're trying to get. That's even worse, you know? So you want to have mechanisms in place to moderate that and sort of squash that down. And that's, I think, conceptually why that's happening.

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If their total energy expenditure on both cases is the same, the Hadza clearly are getting more from physical activity because they're moving all day. Why is it then when caloric expenditure is identical between the two groups?

The physical difference, the body composition is so significantly different. Well, yeah. And I think the answer, the simple answer is the energy in part of the system is changing. Right. So the reason we have an obesity problem, this is the kind of conclusion you're pointed to with these data, is that obesity is an issue of energy intake, not energy expenditure. Because energy expenditure is actually kind of hard to budge.

And I won't say – I get people talk about my work sometimes and say, well, he's saying it doesn't matter what you do. There's no change. I see an enormous number of misquoting of you and misrepresentation of your position. There's no change at all. I said, well, no. There can be some changes, but it's smaller and much smaller than you think. Right.

um and it is true i will also say sometimes there is no change when you give somebody an exercise intervention there are going to be people that you don't see any change in at all they completely compensate yeah but on average everybody compensates a little more than anybody thinks yep um now that means exercise energy expenditure is hard to budge weight gain no matter what anybody tells you is fundamentally about eating more than you burn off right it really is it

Uh, and so, um, it must be on the energy inside. I have seen people use your work as justification for saying things like, see Herman proved calories don't matter.

Yeah, that hurts. It's not calories. It's insulin or it's blood glucose. Yeah, yeah, yeah, yeah, yeah. And to make it really clear, that is or is not your position. That is not my position. Okay, great. I can't see a reality of how people use your work to get to that conclusion. Yeah.

But what you're clearly not saying is that calories in, calories out doesn't matter. In fact, it's saying it is exactly what matters. Yes. Yeah. It's all calories in, calories out. Now, the question is, how do you manage that or manipulate it? It turns out the calories out part's not as easy to manipulate as we thought it was. Right.

That's lesson one. And then I think on the calories in part, why do we eat so much? You know, that's fundamentally the question. Well, I think an evolutionary perspective on that helps too. I think working with folks like the Hadza helps us too because you can kind of see that the dietary differences between a population that doesn't have an issue with unhealthy weight gain versus a population that does. Yeah.

and begin to kind of pick those apart. Now, I'm not, you know, I'm not a nutritionist, so be really clear about that. But I think there are some clear sort of things you can draw from that kind of research. I don't remember the details of the paper offhand. It's been a decade. But I assume the Hadza were not regulating energy intake at all. No, they eat, you know, they're not trying to keep their energy intake low. They're not dieting. And they eat

meat clearly. Yeah. They're eating fruits, vegetables, carbohydrates, fats, whatever they can get a hold of. Is that correct? That's right. It's a mixed diet and it changes, you know, so we can get into this. I love talking about paleo diet and paleo fiction stuff. Yeah, you pretty much crushed that. Because if you live with hunter-gatherers like I've had a chance to do, you know, whatever story you told yourself about what hunter-gatherers eat goes out the window within the first three days. Sure. They're going to eat whatever they can get a hold of. Exactly. And it's going to change day to day and week to week, season to season. Um,

It's the people who I work with in northern Tanzania are not going to eat the same thing as people who are going to be in the Arctic. I mean, of course. Right. Yeah. It kind of all is obvious. It was very a very thin argument. So to wrap us up on this one, what you're then clearly saying is total energy expenditure between the two groups or in bigger between most people then. Yeah. Right. Is probably a groups of people. The individual person we're going to get into that difference. Sure. Sure. Sure. I'm also very interested in that.

But it's likely to stay the same. The energy intake is what's regulating overall body mass for the most part. You gave an example of something like endurance athletes having a down regulation. And it's just an example. Yeah. Of something like testosterone, not because running is bad for you. No. Or bad for your endocrine system, but because it is a strategy of regulating energy output. That's right. That's right.

Because your energy output of your exercise is so high, let's bring down your anabolic energy outputs so that we can keep that total number the same. That's right. And if you look at a group like the Hadza, you know, we've measured testosterone. Well, I say we, the scientific community, have measured testosterone levels in the Hadza. They're lower than your typical sedentary American guy. Lower. Lower.

Right. And that's because they're doing this moderation. We that all fits. Now, I can tell you, you know, if you're worried about the masculinity or the virility of these guys, they're more badass than anybody listening. I would wager plenty of fertility. Yeah. And all that, you know, so it isn't there's no we're not at a clinical level.

You know, but I think what's fun is that you can tie this in then. There is such a thing as overtraining, obviously. And I think, you know, my... You will see testosterone go down as one of the classic signs of that, right? Yes. And so in my view...

It's not just you're healthy, healthy, healthy, and then you're not. In my view, as you exercise more and more and more, you're regulating, regulating. And then at some point, the body goes, oh, boy, we're out of room. And now you're overregulating. You do get into this clinical space where you're too low. But that's the sliding scale. And there's lots of healthy middle, right? And we probably should all be exercising more, almost all of us.

But yeah, but now you can understand it over training syndrome, not as some weird pathology that's, you know, it just happens or you fall off a cliff. But, oh, this is a body's normal reaction and it's just taken too far. You will see a, I could get a line of dieticians from here to Mexico who will tell you about how they've increased energy intake and highly active people and their energy system has recovered. Sleep has gotten better. They felt better, right? Because this is just, it's part of the equation, right? Yep, yep, that's right. All right.

So past that, then the only other thing I want to cover really, uh, or ask you about in this particular topic and is the second big thing I've heard people misrepresent your research and your work and your first book. Yeah. Uh, is the fact that, okay, he's either trying to make, uh, comments about the first thing we talked about, or the second one is the fact, therefore, uh,

Exercise doesn't matter at all to body composition. Thank you. Yeah, perfect. No, obviously, if you exercise, it's going to be good for your fat-free mass. There's some evidence that if you exercise, your appetite regulation is better. So actually, the energy intake side is helped by the exercise more so than the calories expended on exercise. It might be that there's appetite regulation stuff happening. So no, I mean, obviously, exercise is good for a lot of things, including...

keeping a healthy amount of fat-free mass, for example. Right. So you would be an advocate of somebody who's trying to lose body fat that exercise is probably a good activity.

Yeah, absolutely. It's good anyway. In that context, here's the benefits I would think of for somebody trying to lose weight with exercise. I would say, I mean, I will say, I don't think you're going to get much movement on the bathroom scale with exercise. And that's not just my work. That's decades of work trying to do exercise interventions for people to lose weight. And I think that's pretty clear. You know, you can do a year's worth of exercise and the expected weight loss, as I understand it, is about five pounds.

That's probably... You're probably in the neighborhood. Yeah. On average. So, you know, if you are...

overweight by more than that, right? Then exercise is going to be a small part of the solution for you. I think the bigger benefits of exercise are it's a regulatory activity, right? It gets your body kind of working together the way it's supposed to work. We are an active species. And when you take that away, all things fall apart. Yep. So what is then the other side of the equation? What is the exercise not doing? Again, let's just say we're

We're only going to classify this in the perspective of caloric burn. Yeah. There's psychological wellbeing and focus and moods. Sure. All that is true and positive. We're in agreement. Exercise is great. Physical activity is great. Yes. If we're only looking at that calorie part of the equation,

for body composition, what is exercise not doing that people think it is doing? It's not pushing you into an energy deficit where you're burning more than you're sparing it in. It's not pushing you there anywhere near as much as you think it is, would be my guess. And the bigger lever for changing body composition is going to be diet. Right. You know, and so that's whether you can—and that's where, you know,

I think people do have a big, broad range of possibilities. Maybe low carb helps you regulate calorie intake. Maybe, you know, we don't have to have any magic around insulin. You could just imagine that a low carb diet might be a good way to keep you from overeating kind of thing. But no, I don't think exercise has the impact on total calories burned and therefore energy deficits the way that we're often sold it as having. Let's put some numbers behind it. Sure. You could give some examples here, but

If it helps, you can walk us through the additive versus constrained stuff that you've put us together. But if I burn, let's say, 200 to 400 calories in a workout, and it doesn't matter. Let's just say it's an accurate measure, right? Who cares? Yeah.

That's a reasonable number for people to burn and exercise. Sure. You're not probably burning 1,000 or 1,200 very often. Right. That too. It can happen. Some people like, but on average, the person going for a run, exercising, lifting weights, doing a class at a gym, probably 200 to 400, 500 is probably a more realistic number, right? That's right. That's right. I mean, one way to think about that is, as a rule of thumb, 50 calories to walk a mile, 100 calories to run a mile.

Okay. And that's just because of insufficiencies there, right? Yeah. That's walking is just cheaper than running. Yeah. And it's biomechanically more efficient. And so, you know, if you're going to do, if you go on a four mile run, you can expect you burned about 400 calories as a rule of thumb. Yeah. And that's a 30 to 45 minute activity for sort of most people. All right. So we set the stage there. If I'm burning 400 calories, maybe we'll use 500, whatever makes math easier. Yeah.

Why am I not then after a week, seven days, seven times five, that should be 3,500 calories. That should be my pound of fat. How are you trying to tell me, Dr. Ponser, that I'm not losing that pound of fat if I didn't change my energy intake? That's exactly right. So first of all, I'll say that for that first week or so, you might see that initial on the bathroom scale change.

But what's happening is over time, and again, we're still trying to figure out how this all works. So I'm not going to tell you that we have it all sorted out. Over time, we know when you do these exercise interventions, if I measure your total calories burned per day, when I check in on you in a couple of months, in a year, I'm

You think you're burning 3,500 calories a week extra than you were at baseline, but you are not. We know this. You're burning maybe just half that or maybe a third of that. Maybe some people are burning the same as they were at baseline. We see that. And so your body's making these adjustments, and that's why you're not losing a pound a week.

Because you're not actually burning 3,500 extra calories a week. Eventually your body adjusts that and reduces it. The other thing is, it's very hard not to eat the calories you burn. That is also just true. Sure. And so, you know, you say, if I keep energy intake the same. Yep, that's right. If you do, very hard to do.

Okay. What is exactly changing? You can use mechanism here or numbers, whatever is a best way for you to explain this. But when you say my body is adjusting, what is adjusting to keep that total number the same? So we're looking into this now and we have a meta-analysis we're working on in my lab because people have done these intervention studies now since the early 2000s where you give somebody a dose of exercise. I know exactly how many calories per week I've dosed you with. I watch you do it.

And then I follow you for months or maybe over a year. And typically people are getting, you know, something like you're talking about, maybe 2000 calories a week. Right. So that's like adding 20 miles of running to your weekly schedule. We measure them at baseline before the exercise. We measure them.

month six or maybe month 12. And what we're finding is that the average increase in expenditure is only about half or so of what we think we dosed you with. A thousand instead of the 2,000. Yeah, exactly. Where is the energy coming out of?

Perhaps in some studies we see a reduction in BMR, but it's not big. The bigger one seems to be perhaps in sleeping metabolic rate. So if the study had a piece where they had somebody sleeping in a metabolic chamber overnight and could measure that at baseline and then in the intervention, we tend to see some changes in sleeping metabolic rate. The other changes must be in the waking period of your expenditure. Now you'd think, okay, well, they're being less physically active now.

when they're not exercising. They're taking the bus to work instead of walking, something like that. That doesn't seem to hold up because we have accelerometry data with these folks. We know what their 24-hour movement looks like. And the neat part of things doesn't seem to be changing the way that we would expect. So there's something physiological happening, I think, like stress response, like immune failure. We're not capturing a BMR necessarily, but that is helping square the numbers. Okay. That's actually really interesting. I wasn't aware of that. Yeah.

I was thinking of it very differently. If what you're saying is their BMR, because again, let's go back to the total equation. What we're trying to figure out is what part of that equation is changing. And let's assume some percentage of people are in fact eating more and blah, blah, blah. But just as a thought exercise here, let's say that that is not the case at all. You got a couple of things that could be happening. One is we know energy expenditure in the same form and mode of exercise over time will go down. Mm-hmm.

So you'll get more efficient. So that five mile run that used to burn 500 calories now might burn 450 or 75 or 490. You can get some savings there. Yeah, yeah. Right. So now you're getting some small amount of efficiency of movement. Sure, yeah. Okay, great. A few calories there. I doubt basal metabolic rate would go down.

Right here. But what you're saying is it doesn't look like it does maybe a few percent. We can break that one down too. That's fun because if, you know, the basal metabolic rate should be the kind of background stuff your body's doing to stay alive. I'm sedentary. I'm not breaking my muscles down every day with exercise. And my BMR is a thousand calories a day just to give a number.

Now I'm exercising all the time. My body's doing all this muscle repair and I'm still a thousand calories a day. That's interesting. Right? So even when you don't see a change in BMR, I would just put that out there. It doesn't mean that your physiology hasn't changed. No. So this is exactly what I'm getting at. Yeah. Right. So, um, but yes, that alone, right. It should, your BMR should be going up. If you look at the literature across every form or fashion, um,

Changing basal metabolic rate chronically is a really hard thing to do. Oh, yeah. Independent of basically one thing. Yeah. There's only one thing I'm really aware of.

that will change your basal metabolic rate chronically. You can do a thousand things acutely, right? You can take some caffeine right now, but then it's going to come right back down. In fact, your work will suggest it'll probably go below baseline. Maybe, yeah. So that it centers back out, right? Yeah, yeah. The only thing that I'm aware of that will actually chronically enhance basal metabolic rate is an increase in lean muscle mass.

Yeah, that's right. And, you know, I think about we're often comparing across body sizes. So often we're kind of canceling that effect out because we want to say, well, yeah, you had a higher expenditure because you're 200 pounds and this person's 100 pounds. And so obviously there's a difference there. So we're often controlling for body size. I should make that clear. In all these analyses, we're sort of accounting for that too. But you guys don't have

haven't had the ability to, as the way I'll phrase it, it's just not been realistic to equate for lean muscle mass. You generally have to just do body weight, right? Oh, no, no. So we do fat-free mass and fat mass. Now, what we don't do is organ sizes. So we don't do muscles versus brains, for example. Yeah, right. Of course. Yeah.

And for technical detail reasons, getting actual muscle mass versus non-fat mass is a hard sort of thing, right? So the organs matter when it comes to that. Okay. So if it is not

which is a whole interesting thing there, then presumably in the way that people of Boston thought about that is then if you are doing more physical exercise, either your physical activity, and you could call this neat, you could call this a bunch of different things. I can tell you right now, this is not scientific at all. This is just having been around a lot of people who are in the severe caloric restriction for a long time. You'll get what we call the lean effect.

So when you get really physically lean and you get low on calories, you'll notice you just start leaning on stuff a lot. Yeah. You start putting your shoulders on things, like you don't stand there. You're always finding some way to like hold on to some calories, right? Yeah. No, that could be a part of it for sure. I don't doubt that that's a piece of it. What I'm telling you is in these, I think it's, we have 14 or 15 studies in the meta-analysis now that we're putting together. A lot of them have measured with an accelerometer.

So research-grade accelerometer. 24-hour movement. And that doesn't change as much as you would think it would change. It's not accounting for 1,000 calories a day. Yeah. So even if your body is saving 100 calories a day, so I thought you would burn 2,500 calories a day, you're burning 24. That doesn't sound like a whole lot. That's a mile. Yeah. That's a mile run. Yeah, that's your whole workout. That your body figured out how to, I mean, that's amazing. Right. So what does this then tell us, presumably, about our actual understanding of metabolism?

Yeah, I think it means we have to be a little more curious. Yeah. You know, I think that the model that you started off with and everybody starts off with, and I don't fault it, it's a good starting point. You've got basal metabolic rate, digestion, and physical activity. Okay, fine. But there's actually more than that. Oh, there clearly has to be. There has to be, and we know there is.

And everything from stress response to even there's a circadian rhythm in BMR. People, your listeners might not know if I measure your metabolic rate while you're sleeping, it's going to be lower actually than when I measure your basal metabolic rate, which by definition is supposed to be your lowest metabolic rate. That's funny. Yeah. It's not. It's not. At 7 a.m. when you come into the lab fast and ready to get a measurement.

And so there's a circadian rhythm there. And I just, you know, I think I do think this is where a perspective of, you know, an evolutionary biologist, which is kind of how I think of myself is.

I think there's an advantage there. And I think it's available to anybody, so I'm not saying it's... But if you think about the body as a set of systems working together to achieve a goal, which is survival and reproduction, that's how you're built. Now you can begin to get curious about how those systems are going to work together, how they're going to dynamically change when one goes up and another comes down. And now it's a lot more interesting than...

Based on metabolic rate, digestion, and activity. Let's get curious about what's going on. So that's one of the things we're trying to do in the lab now is sort of push that boundary and try to get system metabolic rates because we're very interested in that. I don't know how you're ever going to answer these questions without that. Yeah, I think that's right. I think if you don't know how the systems are changing, if you can't measure it, then this will stay in the realm of trying to match different conceptual hypotheses with the data. And that's never as satisfying as saying, look, I measured...

liver. Yeah. And it burned fewer calories in my athletes than my non-athletes over the course of 24 hours, something like that. Which probably happens, right? I mean, if your muscles can get more efficient, why can't everything get more? I mean, you know, and so I don't think we know yet how it's all going to play out, but that's the next frontier for us anyway, is trying to track that down. Are you going to have to eventually just have people live in a direct

room for six months to answer this? I mean, how are you ever going to answer this without being able to capture every gas expenditure, every thermal expenditure, every

Because that's the only way you're going to get these numbers, right? I think there's other ways to do it. I think there are, like, for example, there are sort of MRI scanning modalities you can use that will get the oxygen consumption of an organ, something like that. And so you can imagine taking snapshots morning, afternoon, because you can't live in an MRI. You can imagine getting snapshots with different interventions about how an exercise intervention changes an organ's metabolic rate or a challenge. You know, if I...

This is a fun thought experiment. You're in an MRI and I give you, I make you, you know, ask you to eat a yogurt, right? You're coming fast and you eat a yogurt. None of that's metallic, so it shouldn't, it shouldn't kill you. Plastic spoon. You're right. Yeah, plastic spoon. We know that about 10% of the calories that you ate from that yogurt will turn into metabolic expenditure that we can measure with a mask. Thermal effect of food. Exactly. But where is that?

Right. So with an MRI approach, potentially you could say I could watch the liver turn on. I could watch the muscles turn on and replenish. I can watch all these things happen. Anyway, we're kind of talking, you know, blue skies, moonshot kind of stuff here, but I think it's doable. And I do think that's the kind of thing that would be interesting to do next. Yeah. A couple of little sub questions going back a little bit. One of them is how.

Should I think about this then for the person that says this guy is out of his mind? I started working out. Yeah. I've lost 60 pounds. Clearly he's wrong. Sort of all these things there. At some point, if I were to run just to make an easy thought exercise example at Surtum, if I were to run a marathon every day. Hmm.

I'm going to lose some weight 30 days later, right? Let's just say water is back to normal, muscle glycogen, blah, blah, blah, right? So at some point, if I'm burning 10,000 calories a day with exercise, clearly the exercise mattered. So with the constraint model, the active model, like how much are we talking? When does it matter? Where's the crossover between when a system won't be able to recalibrate, right? If I'm burning 3,000 calories in my workouts every day, not plausible, so it's kind of a dumb thing.

Yeah, but you get the point. My body won't downregulate 3,000 because then my basal metabolic rate is zero or negative 1,000, right? So how much are we talking when we're getting into this adaptive or additive rather, I keep saying that, additive versus constrained? Yeah. What is the realistic context to some of these numbers? Yeah, yeah. So no, it makes total sense. So I can tell you that we measured people who ran a marathon a day for five months. Marathon a day for five months. Yeah, they took some days off, but they ran from LA to Washington, D.C.,

That's a race across the USA. And it took them five months to run a marathon. And they weren't pushing the pace, but still, I mean, that's a lot of work. I don't care if you're walking it. No, that's right. That's exactly it. And so we measured energy expenditures before they started the race, the first week of the race, and then at the – almost at the end. And this is double-labeled water. It's gold scientific standard. Yep. And it's a sample of people, so it's not just – anyway. Okay.

if you go from the pre-race to the first week of marathons,

Their energy expenditures went up by exactly what you'd expect based on running a marathon a day. Because we know how much running costs. And so we could estimate how many calories extra they should be spending. Sure enough. Do you happen to remember what that number was? It's about 2,600 calories a day, right? Because 26 miles times 100. More or less. So it's crazy because it's not even, people would probably think that's thousands, tens of thousands of calories for a marathon. No, 2,600 calories for a marathon. 2,600 calories for a marathon. On average. Yeah, exactly. Number. Your mileage may vary. Class.

And so, and that's tacked onto what they were doing before the week before we have that measurement too. And sure enough, it's real simple. You take 2,600 calories, you attack it onto what they were doing before, and it pretty much nail exactly what they were burning that first week. Yep. Go five months forward, do it again. And to your point, they are not back to sort of pre-race levels. You can't, not possible. No way. You can't, you can't adapt 2,600 calories.

But they're below what you'd expect. They're below that simple, let's add pre-race to race and they get our answer. And the adjustment's about 600 calories a day. Okay. That's a lot. It is a lot. And so we think that's one way of asking what's the most the body could change, could sort of absorb. And so that's, you know, one thing we talk about in that paper is maybe that's

One estimate of that, about 600 calories. So, you know, you could add 600 calories of exercise, you know, to your life and maybe that would be the most you'd be able to kind of absorb and get back to something like pre-exercise levels. Probably most, I don't know if that's normal or typical or whatever, but that's what we saw in that group. Yeah. So again, you're just giving a broad number. It, as you said, multiple times now, and you've seen this in your work. Yes. For some people, that number is zero.

That's true. Some people that might be a thousand, right? It's kind of there. But what you're just saying is like, it looks like as an anthropologist, as someone who likes to think about the species, that seems to be the number where if you trained really, really, really hard, the caloric deficit that you could kind of hold onto for a long time from the exercise to

Looks like it's capped at potentially around 600 calories. Is that a fair or safe? Yeah, sort of the amount, the maximum amount you could absorb, you can kind of rejuggle in your budget. It's something like 600 calories based on that. Maybe that's a little bit high, but it's in that ballpark. It's not thousands of calories. And would it be fair to say that that marathon a day for five months is the highest caloric expenditure activity that you've studied?

Personally, yes, but that's a fun one because when you look at that maximal expenditure, so they did that for five months. If you look at the Tour de France, it's a higher expenditure, but it's a shorter amount of time. You look at Kona Triathlon, half day, even higher expenditure than Tour de France. And so you can begin to plot out this nice relationship between how long you can maintain something.

and what the maximal expenditure is. And that's something we're interested in as well. And the analogy is like running. You can sprint for 10 seconds, but you can't keep that speed up for a marathon. And so we see that across days as well. You can burn...

a lot of, if you think about it as like multiples of your basal metabolic rate, you can run, you can burn about 10 multiples of your BMR for a day. That jives a lot. Yeah. But you come out to, so, you know, and the fun thing is at nine months,

Pregnancy is the most expensive thing anybody's ever done for nine months. Right? So there's this fun kind of human biology story about how our metabolic limits are shaped by our athletic abilities, but also by our reproductive systems. Right? And so it's kind of all fits in there. I can't let you get away with stopping right there. Okay. I have to ask more about this pregnancy thing. Yeah. If you were to look at the...

The hunter-gatherer communities, right? Now, in your head, again, you're imagining they're so physically active. I certainly know, as an outdoorsman myself, a hunter myself, when I'm out there, it feels like I'm burning 30,000 calories a day. Right, right. Like you're just gone. So to frame this pregnancy thing more appropriately, when we start getting into some of these numbers, what –

Is a hunter-gatherer burning throughout the day? It's clearly, again, total numbers the same over here, but what is their physical activity? Is it 2,600 calories like a marathon? Is it lower? And then what do these pregnancy numbers look like so we can go, wow, like-

Yeah. Without that concept, I think it's going to be hard for people to understand how that pregnancy thing is so wild. Yeah. Yeah. Yeah. So, um, where to start? So, uh, Hadza men get like 19,000 steps a day. 19,000 steps. Okay. So we're told here you get seven to 10,000, right? So they're getting like double. Yeah. Uh, and they're actually doing it rather than we're just told to do it. Uh, women are getting about 12,000 steps a day. Um, and then they hit, you know, often with a kid on their back, um,

and the hard work it takes to kind of get food out of the, you know, often like they're digging into the ground to get wild tubers, that kind of stuff. So there's added work on top of the steps, but the walk-in's the big thing. But to your point, so, you know, they're burning, top-line numbers are the same as you and me. Where does the, how does that all juggle out? Ahad's a woman because pregnancy is so expensive, right?

We know from populations like the Hadza, women are having a kid, and this is without birth control, and they want to have a big family, so they're not trying to regulate that. They're having a kid every two or four, two to four years, right? Whereas in the U.S.,

A woman who's healthy and well-nourished, you know, this is not recommended, but you could have, she could have a kid almost every year. Her body could do that. Irish twins, yeah. Yeah. And so, you know, not recommended, just real clear. But that's because of the energy availability that's there to handle what is the most expensive thing the body can do, which is pregnancy. Okay, so what you're kind of saying is...

When you were talking about the virality and fertility of the male side, perhaps the female side, because their expenditure is so high, that perhaps something physiologically is

Is intentionally lowering that fertility so that they don't have kids too often? Is that kind of what you're referring to? That's right. Yeah, the body is just— You don't know that directly. You didn't study that. But, like, that's kind of the thought trainer on here, right? Well, and, I mean, we kind of have a lot of—there's fun evidence about that. So if you take—in other populations where women are doing a lot of work to go get water every day—so these are populations in Ethiopia, I think, but also in Central America—

Women are, one of their typical tasks in a typical day is to go and get water for the family. And it's a huge amount of work. You walk on a kilometer to get a whole lot of water and water's heavy and you bring it back. And then in a couple of these studies that are just wonderful little kind of natural experiments, you add a well in the village. And now mom doesn't have to walk to go get water anymore. And fast forward a couple of years and you're like, oh, family sizes got bigger. And the time between kids got smaller. Yeah.

And that's because you've taken this activity cost and you've taken it out of their energy budget. And now the body is able to kind of

recover after a pregnancy and be ready for the next pregnancy faster. Okay. Makes sense. Um, it's not necessarily a, I'm assuming you're, you're equating for in all these studies, overall sex activity and things like that. So it's not like that's probably going down somewhat, but that's not explaining all of this. That's right. That's right. And it's, it's, um, no, we, these are populations where people would love to have big families. Yeah. Um, and yeah, that's, that's the issue is, uh, you know, physiology, not behavior.

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And what is this difference in like a Hadza female total daily energy expenditure? And then what happens, whether it's them or in non-hunter-gatherers, like what happens in terms of energy demand during pregnancy? Yeah. So Hadza women... That's quite the claim. This is the most expensive thing we'll ever do as a human. Yeah. Yeah. For nine months. For nine months. Right. So a healthy human pregnancy costs about 75,000 calories. Total. Total. Okay. You spend most of that in the second and third trimester.

And if you are a Hadza mom, you've got to do that while also maintaining pretty high levels of physical activity. That does come down a little bit, just the mechanics of foraging when you're in the third trimester, I'm sure is hard.

But, yeah. So I'm not sure how you want to break it down, but that's, you know, so, okay, here's another fun thing. And this is the kind of stuff you learn when you start moving your sort of field of investigation beyond a westernized, industrialized context and start looking elsewhere at what human diversity is all about. There are farming populations, a great study of farmers in Gambia. This is going to sound like a real tangent, but it's not, I promise.

You've got women who are working really hard doing agricultural work. Their total energy expenditures are still kind of more or less the same as everybody else's, but on the higher end, let's say, the higher end of normal. They measured them through pregnancy and they don't change, right? They're able to maintain in that context where food is a bit limited and, but activity levels are high and mom's already kind of pushing her limits probably even before pregnancy, right?

it doesn't get pushed much higher during pregnancy. And that was a study done in the late 80s, early 90s. And so it seems like, you know, the most mom can do for that nine months is pregnancy. And even if you add physical activity on top of that, there doesn't seem to be a lot of room to even move beyond that ceiling. And we got, I'm presuming you have to partition out to the child. Yeah, that's right. So the baby gets protected, baby is healthy, and mom takes the hit. Yeah. And...

If you were to contrast that to these marathon numbers, Twitter France numbers and stuff, like what? You said 75,000 total calories for a normal pregnancy. So how much is energy expenditure on total differ between a pregnant female versus a non-pregnant? So a normal daily energy expenditure would be about 1.7 METs, something like that. Yeah.

In pregnancy, that'll go up to about 2.2 METs in the highest expenditures for a sedentary population. We're trying to figure out right now if that changes if you have active moms in the U.S. We don't know what the results are on that yet, but the expectation is that that 2.2 METs for nine months is really high.

the max of what the body can do. And that is, that is an enormous amount. And then that is more than this marathon running thing. This is more than tour de France stuff. Like this is a really big number, right? Well, so if you, the guys who ran across LA to DC, they were at 3.5 Mets for that five months. There you go. There's your context, right? Yeah. Male versus female. So it should be generally higher anyways.

and running a marathon a day. Yeah, 3.5 minutes. And then Tour de France, you can get up close to five minutes, but it's only 28 days. Sure, right. Right, so that's the trade-off. It's like duration for maximum expenditure. So it's almost like you're halfway between here, right? So you're not short month Tour de France. You're not five months for this running thing. You could run a marathon every day for nine months and not burn as many calories as you would

Having a kid. No, no, no. I don't think that's right. I think close. I think a marathon a day is still more, but you couldn't, you, how about this? For nine months, we think the maximum a body can do is about 2.5 mints as max. Moms, think about this, moms burn 2.2, but then they have to also eat extra to gain weight. That's right. So this same study of duration versus maximal expenditure, just to kind of reset ourselves, the expectation is that the longer you go,

the lower that metabolic ceiling becomes. At about nine months, that's where moms are. And that it kind of flattens out. And the long-term ceiling for everybody is about 2.5 METs is the expectation from this study. And that means that whether you want to be an ultramarathon runner training for your next big thing or a cyclist or whatever, or you just want to be super fit and exercise a lot, you're still capped long-term at about 2.5 BMR.

And that's the same cap for that mom's under basically. Right. So that's the, that's what we're talking about here. Yeah. It makes intuitive global general sense. Yeah. Right. If that number shakes out. So in the case of something like pregnancy, because you're going to preserve it for the developing child, that means mom's physiology, as you said earlier, is going to take the hit. Yeah.

Same thing happening with the overtraining situation. Yeah, it's the same juggling, right? It's the same over juggling kind of thing going on. So that means your immune system or your endocrine system, some metabolically active part of your life is going to have to go down. Hopefully that it recovers. But if it doesn't, this is why you see people getting more sick when they're overtrained. This is why their libido goes down. This is why sleep and other things go down. It's in large part because of this energy. You can...

Talk about it from the hormone perspective. Right. But the hormones are a response. Yes. Yes. They're the signal because of this energy flux being off, right? That's how I see it. Yep. If you look at the folks that pay a lot of attention to what's called REDS. Oh, right. I'm sure you're familiar with that, right? How does that fold into this equation? Maybe just walk us through a little bit like what REDS is. I know you're not a dietician. Yeah, yeah, yeah. So, and let's see if I can get the acronym right. Relative Energy Deficiency Syndrome. Yeah, there you go.

I'm a simple man. And in my mind, REDS is just kind of another way of talking about overtraining syndrome, basically. It's the energy side. It's the energy side of it. That's right. And, you know, one way to think about REDS is you're not getting enough energy in.

But the other piece of it is you can – there are studies where they supplement athletes and that helps. That's great. But you can – there are athletes who won't respond to that. So I understand it. And I think it's because – my suspicion is it's because they've actually hit the energy ceiling cap and they really can't put more energy through their bodies. They're not able to do that, to take advantage of those extra calories. Yep.

And so that's the expenditure cap of it. Yeah. And it's typically when we talk about reds, we're talking about female, right? That's just, it's a way to describe what happens when females tend to be really active and oftentimes get really low amounts of body fat, body mass, right?

And then they have a whole host of things like amenorrhea. And I mean, you name your debilitating bones being more brittle and breaking and things like that. And so typically you're going to do a combination of two things or one, at least you're either going to reduce physical activity. Right. Or you're going to increase intake or both. Right. Yeah. Yep. Which is your typical treatment. And there's more to it, but that's right. That's right. But thinking about these energy caps on that, you know, what is the ceiling that I'm working under? I think one pragmatic thing to take away from that is,

if the supplementation is not helping, it's not because you're doing it wrong. It might be because you're at the ceiling. And then you take some training away and you might get a kind of less is more outcome where you're actually healthier and able to maintain higher overall workloads because you're not dealing with downtime from being sick or being injured or something like that. So in that particular case or in other cases, when people have

felt like their metabolism is slowing down all right this and i've seen this in plenty of our high performing athletes and non-athletes we deal with where legitimately they used to do the same workout before eat the same things and the same relative amounts and now all of a sudden progression of weight is is different right um again you'll colloquially call this like my metabolism slowing down right you and i both know that's not what's right your metabolic speed is not changing yeah

Clearly, this is a total energy expenditure issue. What do I do about that? What do we actually know scientifically? Can you raise this number back up? Yeah. If so, how? I'll feed you a little bit before we go on this one. The answers you'll often hear are things like, well, increase lean muscle mass because muscle mass is active and it burns a bunch of calories. Mm-hmm.

What do we actually know about the ability to, again, it's not the right term, but how people were going to hear this, you know, raising our metabolism like that. So I don't feel like I have to eat a thousand calories a day, which is really, really hard to not gain weight. Yeah. Yeah. I mean, this is, that's, that's the big question. Be a nutritionist, be a dietitian for me, please. So yes, fine. First of all, I would say feeling like your metabolic rate is slowing down doesn't necessarily mean your metabolic rate is slowing down.

And so, you know, we've measured, for example, daily energy expenditures in non-athletes. So these are just typical folks. But from about, you know, early 20s till about late 50s, people's energy expenditures, daily energy expenditures are not really, we don't see like a slow down in middle age. It doesn't have, I mean. Say it again? Yes. Your metabolism does not slow down in middle age. And look, I'm 47 and I feel like it did too. Yeah. Yeah.

But it doesn't. I mean, you know, those are the data. You and your science lies, Harmon. And here's another fun one. You know, this is another great example. It's like the Hadza data where you've got the data and you've got your preconceived model and you have to choose because you don't get both, right? You will see pretty routinely now, people will talk about things like

Bone health. People will talk about muscle size, muscle strength. People will talk about things like HRV, that these things all will decline with age. VO2 max, cardio, sport, fitness. Sure, sure. All of those examples have been now shown to not actually decline as long as activity remains the same. Yeah. What you're also trying to tell me, this evil lie, is that you're saying metabolism does not slow down with age.

On average. Yeah, that's right. Yeah, we have, you know, this is a study of 6,000. Justify yourself, sir. Thank you. I will. So we have this, it's actually a really fun science story. We have a big international consortium now, people sharing doubly labeled water measurements across studies. This is the, is this the global human metabolism database? Yeah, the doubly labeled water database or something like that. Yes. And so you've got my lab and a bunch of others all sharing data. It's a really fun science story that way.

And we've got, and now it's, I think it's 10 or 11,000 measurements of people from eight days old up to people in their 90s.

So this is a full snapshot of human metabolic diversity. Men and women, active, inactive, healthy disease, whatever. Yes, yes, yes. Everybody. And so we can really say something that we can stand behind about what, for example, what does metabolic rate look like over the arc of a lifetime? You published this already, right? That's right. That's right. It's a 2021 paper. Lifelong metabolism paper or whatever. Yep. That's right. And so there's some really fun stuff. When you're born, you know, well, first of all,

One thing that you get right away, which is kind of obvious, is that bigger people burn more calories. Body size, right. Body size. Men and women, when you correct for body composition, burn the same. You're going to have to say that one again, particularly when you correct for lean mass. Yep, that's right. So a 150-pound man and a 150-pound woman, the man might burn more calories on average because men tend to carry less body fat for a given size.

But now let's ask the question differently. 150-pound man, 150-pound woman, both the same body fat percentage. Imagine the expected expenditures, the same. You would, in looking at those people, you would think in that case, the woman is a lot healthier, leaner, because at the same body composition, a woman will look a lot physically leaner than a male. It's because normal. But when you equate for those two things,

Yes. Their total expenditure is, you would not be able to be like, that's male, that's female. That's right. That's right. I mean, it comes back to this 37 trillion cells doing their jobs. And when it's the same composition of cells, the same fat-free mass, the same fat mass, they're all kind of doing their thing. Things like sex differences disappear from your results. You don't see it. Okay. There's a whole bunch of stuff I want to ask about this in terms of, are we then thinking about human capacity, human systems, adaptability as individuals?

you know, your book, your new book is wrong. But before that, to finish our little story here, so we don't see in this giant database now using, it's all doubly labeled water. That's right. I will say that we get the same pattern with basal metabolic rates.

So you have two modalities giving us the same answer. So it isn't like, oh, this measurement has a problem. Just to be clear, because that's always the follow-up. That's more interesting, right? Yeah. Because now you're using two different methodologies for that same measure, and they're both at least aligning. That's right. Overlapping in a pretty high correlation. Yes, yes, yes. Okay. So no differences between the sexes.

Generally, no differences past, what, probably age 20, 25. When is that? Yeah, I mean, you kind of, you know, biology doesn't take hard corners, right? Things kind of mellow out. So around 20 to 25, somewhere in there, you hit kind of your adult rate. And then you're just rock steady until late 50s, early 60s, something like that. And then it begins to decline again, which is interesting. Mm-hmm.

Because we know that later age is when things like diabetes risk, heart disease risk, dementia risk, all these things kind of inflect up after 60. And your metabolic rate is inflecting down. And these are all body mass, body composition controlled. So it isn't just sarcopenia because that happens too. And

And so I think we're seeing cells slow down. Yes, we're seeing cells slow down. We're seeing the body slow down. And that's related to, I think, this increased disease risk. All right. So I got one question on each side of the age spectrum. Sure, sure, sure. I know you got some new work. I think you got a new NSF grant for doing a bunch of stuff with adolescent girls, right? So you've got some experience in the children's side of the equation as well as now past 50. So two-part question. One of them is,

How much higher is generally energy expenditure per

When it is peaked, right? I presume it peaks at puberty or close to it. Oh, it peaks at size corrected expenditures peak when you're one years old. That's your... Boom. We've all peaked too soon. Yeah. We've all peaked too soon. That's it. So you lied to us earlier. It does go down a phage. After one, it goes down. That's right. You're right. One to 20. Yeah, yeah, yeah. Yeah, a little baby, you know, one year old infant is... Their cells are just super busy, right? And you see that in the calories they're burning. Now, look,

Look, they're also tiny. So total calories a day is not impressive. But when you correct for body size, it's 50% higher. Yeah, it's a lot. And if you could shrink an adult down to that size, the baby's burning 50% more calories than the adult. Yeah, well, I mean, it's turning over its entire skeleton in a year. Like everything is really around. Yes, yes, yes.

But when you get into your teenage years, how much higher is that expenditure is, whether it's teen or whatever? Yeah, you're coming down, you're coming. And so, you know, it's sort of a sort of a glide path. And so, you know, by the time you're 10, you're probably around 20 percent higher than you would be as an adult. And then slowly it's going to kind of come down. Yeah.

That's the kind of ballpark, 20, 30% higher. So when your teenage kid comes home and eats the entire fridge, yeah, that's real. Yeah, yeah. That's because, you know, their metabolic ratio is higher just because they're still developing. And do we know what part of the metabolic equation that's coming from? Is it all of it? Do we know? So again, we see the same pattern in BMR. That doesn't really answer the question because your BMR is all your organs playing around. So we don't know which organs are doing what. So the brain is super expensive. Even in an adult, the brain burns 300 kilocalories a day. Yeah.

Whether you're dumb or not. I like to remind my students. Actually, probably more if you're more dumb, right? It just feels that way. More dumber. Yeah. So, you know, when you're a kid, it's probably even higher than that because not only is your brain doing its expensive thing of thinking and regulating, it's developing. And so all the organs are probably doing that. We don't know. Another frontier is how to thing to do. Let's figure that out. I ask that because we...

And colloquially, we'll hear things like, well, oh, man, yeah, I played all these sports as a kid. And so I was lean, but now I'm not playing sports anymore. And so people will tend to justify that 15 to 20 pound gain in their early 20s. Yeah. As well. I just stopped playing sports anymore. And then they rush back into the gym. Yeah.

Don't often see a lot of results and then partake in sedentary activity for the next 20 years. That's right. So how are we thinking about that incorrectly? Yeah. Also, I mean, I think that the higher expenditure that you had as an 18 year old, you were at the wonderful tail end of this elevated metabolic rate that you get for free. Yeah. Just from your development.

You hit 21, 22, 23, and that goes away, you know, and that usually coincides a lot of life changes. You get your first job, et cetera, et cetera. It all collides. But yeah, I think the big bump that you thought was because you were playing baseball is actually because maybe the bigger bump is actually just because your body was still developing. Yeah. So it's almost really a combination. Generally, people are way less physically active post high school. For sure. Yeah. They're probably also maintaining the same nutritional habits. Yes. Yeah.

So it's all of those things. Yeah, that's right. That's right. And, you know, look...

Stress is an issue. Sleep is an issue. All these things that push us to eat more. Yeah. Right. I mean, all of a sudden I'm stressed out all the time and I find myself eating more than I did before. You know, things like that. Yeah. And that that more than some kind of global change in your metabolic rate in your 30s is kind of what's, I think, really pushing things around for people. Yeah. Then let's go the other end of the age spectrum. Yes, sir. Now, what happens? And I am, you know, OK, we'll say this. It's fair to say.

If you want to think about it this way, your metabolism slows down past 20. They have that big bump when we're 10 or 15, 12 years old, whatever. It does start to glide down, as you're mentioning. It levels out mid to early 20s. It holds on for the next 30 or 40 years. So you can blame those pounds you gained as a 20-year-old.

But you can't gain those pounds you gained as a 40-year-old. Yes. Most likely on it. But it will now start to decline even as you're saying when you correct for maintaining muscle mass. Right, which we know is harder past 50s. Really, really hard, right? So let's just say you were able to maintain that thing. Do we know what is happening now?

Both mechanistically as well as, again, what part of the equation post-50, if it's not loss in muscle. Because if you were to ask me right now, I would say, I bet it doesn't happen as long as you hold your muscle. Oh, yeah. That would have been my guess. Yeah. So I don't know that it's that easy. Damn it. Yeah, I know. Because, again, this is paired with basal metabolic rate measurements. It's supposed to be easy.

It's more fun when it's not, but I agree. It's not, yeah. The stories are simple. You're a teacher. You're a storyteller. Yeah. It must be easy. Come on, Doc. Yeah, yeah. So it could just be, you know, that you lose muscle mass and your metabolic rate goes down for that. But we correct for that and we still see it. Oops. Okay. Next explanation. If you do basal metabolic rate measurements along with this, which we have in that same data set, you see that, you know, for a given...

Fat-free mass. So for a given organ sizes, you hold organ size and muscle mass the same. Metabolic, basal metabolic rates even at rest are lower, pat post 60. And so the only way you can get that mechanistically is for the cells themselves to be slowing down. Now, you're asking a different question, I think, related but different, which is if I'm physically active,

And one thing that will happen is I'll keep my muscle mass up, maybe. But the other thing that might happen is, again, exercise is a regulatory behavior. Yep. Right? And I'm signaling to my body to keep going. And, you know, that's a very hand-wavy way to talk about it. But there's something about that regulation of activity that might keep all your cells more active. Yeah.

Okay. I'd love it. Let's test that. I mean, I think that's possible. I don't think we would know that for sure right now. Generally, we associate aging with inefficiency at the cellular level. Yep. Right? So you're losing either actual cell mass, things are dying, breaking off, going down, or they're becoming hyper inefficient, more leakage. Yeah. Which I would think would actually then make energy expenditure higher. Mm-hmm.

What am I missing here? I think you could have two things happening. You can have inefficiencies and just lower output overall, right? I mean, again, the only way you can make the math work on these measurements of expenditure, and you get it from both modalities, so it's not just a methods thing, is that it has to be the case that...

A liver cell, you know, to pick an organ, I don't know if this is the right one. A liver cell in a 70-year-old burns fewer calories every day than the liver cell in a 40-year-old. And it kind of has to be that. Now, is it the liver or is it a different organ? And that's the interesting set of questions. Yeah, but one of them. It's going to have to be one or a combination. Something has to be changing. You think this is a function of...

Looking at, I would not say exclusively, but primarily cross-sectional data versus having more longitudinal things like that. Is that? No, that's a fair point. I mean, these are big cross-sectional studies. I don't think you could, I think there has to be a longitudinal signal in there to see the big data trends that we see.

But it is true for all sorts of obvious reasons that we don't have data from somebody who's 40 and then 50 and then 60 and then 70. That would be a study that's still happening and started 40 years ago. We don't have that yet. Yeah, but I mean, geez, we should. I agree. We should start it, right? I agree. I agree. And that would be something we're really interested in is sort of get you at 55, get you at 60, get you at 65 and see.

What is the longest that we do have? Do you know? Do we have any two-year studies? Do we have any five-year studies that have... We do. We have two and five-year studies here and there, small ones, but not that I know of in that critical post-60 age group. The ones I know of are in people's sort of, you know, prime adult years. And that's interesting. There you find individual differences, right?

are pretty static. So if I measure you today and I see that you have a high metabolic rate and I measure you again in two years, I'll see that you have a high metabolic rate again. And it kind of even independent of what you report anyway as lifestyle change. If you're slow, you're slow. If you're fast, you're fast. Now, the good news is

It doesn't seem to have a big impact on whether you've gained weight or lost weight in the intervening years. Yeah. So that's another kind of myth, right? People think, oh, my metabolic rate's high. That's why I keep the weight off. Probably what you are experiencing is a better relationship with food that you aren't being pushed to overeat the same way that somebody who says, oh, I have a slow metabolic rate is overeating.

maybe more food focused and it has that different relationship with food and is having a hard time that way. It might not be metabolic. In fact, it's not metabolic rate. I'll say that. It's right. And here's my metaphor for that. You walk into a bar, you want to play some darts, right? And they've got the dart boards hung on the wall and you're throwing your darts at the ball. You don't know if that dart board is hung a little high or hung a little low. You just know you're trying to hit it. And that's what your body's doing with expenditure and intake.

It doesn't know if you happen to have a little bit of a high metabolic rate or a little bit of a low metabolic rate. It's just trying to balance the budget and hit the center of the bullseye. Right? So if I came and said, oh yeah, your dartboards are hung a little high, I'm still going to find that the darts are stuck around the center because people are still aiming at the center. They're not aiming at what they, you know, some global middle dartboard height. They're aiming at that one. And that's how your body works. You're aiming at that metabolic rate. And so if you're high, you're high, that's fine. But missing the bullseye

And gaining or losing a little bit of weight is going to be independent of if the guy next door is aiming at a slightly lower dartboard. Yeah. So if you take the person who says, I eat all the time, I'm constantly stuffing my face, I never gain weight. Yeah. And you contrast that to the person who feels like they're doing the opposite. What you're saying is most likely-

that energy intake for the person that feels like they're stuffing their face is probably not as high as they think. Yes. And vice versa, the person who says that they're not eating a lot doesn't feel that they are, probably is eating more than they think. And that's, you know, we've known that for a long time, that people under-report. Yeah. Sometimes they over-report, but usually they under-report. And there's all sorts of obvious reasons about that. That's not intentional. Nobody's, you know, I'm not saying people are lying. That's not the point. You just, people have a hard time tracking what they do. Yeah. I would say in my experience, the people who feel like they're the former,

The I can eat anything I want. They end up going through really long periods of not intaking food. Yeah. So they'll be like, oh yeah, I ate a whole pizza last night. You're like, oh great. And then they had a yogurt for breakfast. Right. And then they had a lunch they had and you're like, oh. So actually you feel like you're feasting all the time. Exactly. Where the other folks are way more consistent about their food intake. So it feels like

And clearly there's more to it than this, but that's been my experience of being like, I actually don't eat that much. You just go through waves of eating. Yeah, that makes sense. Yeah, totally. Do people tend to be more physically active, whether it's exercise or activity, in periods of short caloric surplus? So if I eat a whole bunch more this weekend, am I going to be more active next week? I don't know any data on that. That's a nice prediction. You could imagine sort of evolutionary reasons that those mechanisms would exist. Yep.

Good question. Yeah, I don't know. - 'Cause then we don't know the opposite, I assume as well, right? So if you pull calories a little bit this week, are you gonna be, 'cause you hear people say these things, right? "Man, if I pull calories down, I just, I don't move." - That one seems, you know, the fatigue response and we know that if you really crash diet, your basal metabolic rate can go down as a response. - Oh, sure, yeah. - But you're not talking about, you're talking about something smaller than that.

Yeah, gosh, I don't know. It seems like a real easy one to measure and maybe people have done it, but I can't think of a study that's looked at it. Today's episode is sponsored by 8sleep. 8sleep makes smart mattress covers with cooling, heating, sleep tracking, and more. I've personally been sleeping on an 8sleep mattress cover for years now, and it's absolutely glorious.

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And I'll say it this way. I generally have had more disdain for the world of anthropology than I have had love. All right. Okay. Okay. It's not the work of the scientists. It's generally the media and the interpretation. It's not your guys' fault, right? What I'm getting at is the natural fallacy. Oh, yeah. And so I always have a hard time getting through things like

Okay, what can we learn from anthropology? What can we learn from looking at culture and looking at ancient humans and how things that matters without making the natural fallacy? Yeah. I feel like you've done a really good job of that.

now in our conversation as well as over your career. So how do we think about these things properly, getting the best out of studying ancestors and anthropology and if that's even biology and not making natural fallacy? No, that's right. So I think the value, let's start this way. The value of looking at a broad sweep of cultures in general is that you're going to capture more of what our bodies can do

and more of how our bodies respond to changes and differences in lifestyle and ecology and environment. All these things we're interested in, but we only have a really narrow view when we only look within the U.S., for example, or within, you know, urban centers in the industrialized world, right, where most research happens, by the way. So I think looking across cultures gives us a real sense of what real biological diversity looks like, how interactions with environment look like, how that interplay happens.

And then the evolutionary perspective is it gives you a kind of working hypothesis, a working model for expecting how the body will work, how it will respond, what the body is trying to do. The body is not trying, you know, your body isn't evolved to make you look great for the beach. Your body isn't evolved to lift, you know, to be a massive bodybuilder necessarily or whatever it is that you're trying to accomplish.

understand what the body is kind of organized toward, the organizing theory of the body, which is evolutionary success.

I think helps you make sense of the physiology. Why does my body adapt to physical activity the way it does? Well, because we're a physically active species and have been for 2 million years. And so, you know, our entire physiology is organized around that. You take that away, you have problems, right? So I think that's the advantage. It isn't to say, oh, a hunter-gatherer lives this way, therefore I'm going to...

cosplay like a hunter-gatherer and be healthy. I mean, that's silly, right? That's goofy. I'll give a couple of direct examples. Yeah. I think that was great, by the way. That was actually really helpful. When you hear justification of a particular methodology, it doesn't matter, diet, exercise, psychological, relationships, you pick how humans interact. You could fall back to basically any time point

Find some previous part of our history in which people did it this way and justify it, right? This is the natural fallacy of, I skipped over, I know you know, but is the idea that just because it is natural, then therefore that is correct. Right. There are a lot of things that are natural that we don't want to do anymore. Right. We don't have to list them, but you can imagine ancient humans did some activity in a certain way that we don't want to do anymore as a culture. Yes. You see, that's not okay. Yeah, yeah, yeah.

Fill in the blanks, folks, if you want there. Cannibalism is a fun one. Okay, great. Right? You can find a population. There's documented evidence in the past of people, different populations, who practice cannibalism. Now, why and how, those details are an interesting question, but nobody would advocate now...

that that's a great thing we ought to be doing. I'm sure somebody would. Yeah. I'm sure somebody would, right? The world's a crazy place, but most folks are not going to want to do that. So if the natural fallacy exists, then why does it matter at all that we study all people? Oh, yeah, yeah, yeah. No, I mean, again, that gets me back to this diversity thing, because if you want to know what a really physically active day-in, day-out lifestyle looks like,

Or, you know, how our bodies juggle those demands. Well, then let's go and ask that question. Let's go find populations that are really physically active. Let's find ones that are sedentary. Let's find ones that eat a really high carb diet. Let's find ones that eat a really low, you know, high meat diet. And that's a way of asking about that diversity. I think you also learn some other interesting things. You learn about local adaptations in some cases that you otherwise would miss. But I think that's the advantage is diversity.

In terms of when we want to bring it back home to a health context, right? What we're going to learn about how we're going to fix our own lives today. That's it. You're learning about the sort of the diversity of human experience, and you can pick and choose the lessons from that. Not in a naturalistic, fallacy kind of way, but in a, hey, they've tried it that way, and this is how they result. This is how their body results from that. I can bring that home. Great example. Physical activity we know is important.

for lots of reasons, but like how much should you get, right? That's a fair question to ask. And it turns out that if you look at how much, this is just a fun little comparison. If you look at how much physical activity folks get in a nice study that was done in Scotland, it's, where was it? Glasgow. In Glasgow, it's Glaswegian mail carriers. All right. This is a fun one.

You have folks who are carrying the mail every day getting 17,000 steps a day. You have folks who are in the office sorting mail and they're not getting the steps. And you ask, who has the best health outcomes? And it's all National Health Service up in the UK, so it's all kind of controlled that way. The real big difference here is how active you are. The folks who are getting the 17,000 steps a day are, turns out, really well protected against cardiovascular disease and all these things. Well, yeah.

How do we understand that? Well, it turns out if you look at, you know, traditional groups around the world, that's kind of the sweet spot of where people are getting their activity. That's how much they're getting in a hunting and gathering context or a farming context. It matches up. And so that's, you know, not that those male carriers are thinking, gosh, I want to make sure I get as many steps as a hunter-gatherer today. That's where we can learn something from another cultural context, another

you know, a non-industrialized context and it helps make sense of the practical things we can do in our own lives here. We don't have to act like hunter-gatherers. That's not the goal. The goal is to learn. Yeah. You and I are going to focus on physiology. Yeah. Metabolism and exercise. Great. But you can find these same examples in

cultural and relationship and how people interact. Like we're just going to focus on this aspect of, but I really think it's important that people extend that thinking out to this is all of how we behave as a species that can go there. So with the, uh, I don't know if that was stuff in the UK biobank, but in the Glasgow, uh, example there, you're highlighting another positive role of physical activity and exercise. Mm-hmm.

but just not from the caloric expenditure. Yeah. Right? I mean, that's kind of what you're saying is you're not denying and suggesting that so many people and so many magazines and articles have said that you're saying there are plenty of physical activity benefits. It's just perhaps not from the caloric expenditure side of the equation. That's right. Right. Right. So I just want to triple quadruple down on what you don't say. Right. But getting back to this, how do we then decide which of these learnings

from anthropology that we choose to take, like physical activity, but then we don't choose to take the cannibalism one. Right. Well, that gets to this question of, you know, biology can tell us how things work. Cultural studies can tell us the diversity of what possibility spaces are. You know, but then it all ends up, you still have the hard decision to make yourself as in, what are my principles? What are my principles?

you know, guiding ideas and how do I bring this into my own life? So that's why you're probably not going to bring cannibalism in, but you might want to exercise. Yeah, fine. You know, and I think there's also a broader importance here. And that is, I think,

We reduce a lot of how we study the natural world and study ourselves down to what's the next thing I'm going to do to tweak my life, to give myself more energy, better health, whatever. Those are all important things to have. We should all want to maximize our time here. Absolutely. But there's a broader question, which is how do we understand the world? How do we understand ourselves? How do we understand ourselves?

everyone around us. And you're not going to get all those answers with blinders on, narrowly focused on your neighborhood and your immediate area. You're going to get those answers, I would argue, by casting a pretty broad net, asking what's going on around the world, even in different species. But, you know, let's keep it to our species for a moment, asking those questions about what happens in different cultures and different contexts. And I think there's a richness there

that actually does improve our lives in ways that are harder to measure. But that, you know, we often want to reduce things down to the bottom line, to the health nugget, to the biohack. And okay, I get it. But there's a broader thing here that I think is valuable. Right. Very, could not agree more. Really well said there. How much do we know about the variation? And let's just stay with our wheelhouse here of something like energy expenditure among other things.

older forms of lifestyle, if you will. So clearly you've spent time in Africa and I don't know if you've gone to Central America, but how much variation do we know exists between Southeast Asia cultures, European, Scandinavian and other ones? I assume you think your findings with the Hadza group would extend to

everyone else, but what do we actually know, if any, about other groups? Great question. So now we have this big global database that we're putting together has allowed us to kind of ask that question, which is really fun. And so we've got, in the latest iteration of it, I think we've got 35 populations from around the world, everything from folks in, you know, traditional folks with their herds in Siberia to Hadza in there, to U.S., I mean, we're all in there. And, you know, what we're finding is that

There are some interesting differences between groups. They're pretty small. They don't track with activity the way that you might simply think that they do. But there are some interesting context, interesting things happening there in terms of average differences between groups. But the variation within a group swamps any differences between, average differences between groups. And so if I say I pick a person from Southeast Asia and say, what's their energy expenditure? It won't help me to know that they're from Southeast Asia because

Because actually there's the variation within the population is so much that. I'm so fascinated by this thing because in full disclosure, you were kind enough to send me a copy of your new book. Yeah.

which I was going through and I'm thinking, this is the exact opposite of anthropology. And one of my other gripes with that field is you're studying giant populations and you're completely forgetting about individuals. And you're now just saying, because I'm from X region, this is my physiology, which is always irritating me having coached and worked with countless people. And I get this question all the time.

What have you found different between your females and your males or how do you treat them or fill in the blank? Yeah. Your power lifters versus your endurance. Yeah. My answer is always, I don't really have any answer to you that is categorically different. Yeah. So I feel very validated in your new book of saying even the guy who does this and looks at big populations of people is going to come back and make a pretty strong argument that that's potentially not the best way

To look at it? That's right. Yeah, I mean, I think what you're— Thank you for letting me do that, by the way. No, yeah, yeah. Have you had enough? Do you need some more? No, I have so much more to say, but go ahead. You know, so that's where this new book came out of, was not just thinking about how metabolism varies, but just about how our bodies vary and how our bodies work. Yeah.

across systems, you know, brains, hearts, lungs, livers, spleens, how it all works. And in every one of those stories, it's really, you know, your body is a series of stories and every one of those dimensions of you can vary. And people just don't, first of all, don't understand how their bodies work. I think fundamentally, teaching physiology for 20 years, that seems to be what I take away from that. People walk in the door fresh from high school, but not knowing how muscles work really, or how hearts work, or how brains work, any of it.

That's too, we need to do better than that. But the other thing is when we teach it, and I know what your experience was in your training. I know that my experience was, you know, you get the textbook human. That's how you're trained. And whether you're taking gross anatomy at Harvard Medical School, like I had a chance to do, or you're doing, you know, whatever your training is in human physiology, the people who taught me had a very, and I think this is true generally, have a real,

How do I put this?

there's a kind of struggle with how we talk about diversity. You're taught the textbook human, right? Because as soon as you start talking about differences between people, people get super nervous for all sorts of reasons because there's a real nasty history there about how we think about human diversity and we get it wrong and we divide it up into racial differences or sex differences. And all of a sudden we're in really, you know, first of all, we're way out of where the science is. And secondly, we're into some really ugly history and culture there.

So people don't want to do it. And so we don't have the tools to talk about diversity. But when we can do it right and we sit down and think about how our bodies work and how we vary across individuals, now we have the tools. And we can sit down with somebody and say, it doesn't matter to me that you're Asian American or that you're black or that you're white because I'm going to treat you like an individual and you're going to be different in all your dimensions and

than somebody else might be. And that's how we're going to talk about your body. And that's how we're going to treat you. And so that's what I kind of wanted to get at with the book. Clearly, what you're indicating is all of those factors matter. Yes. They all matter, right? So it's not that I'm saying I don't care what your ethnic background is. You're saying I do care, but this is part. Yeah. I care only enough to then ask more questions about your complete picture. That ethnic background, your genetic inheritance, you pick your

your variable here, is only a part of the equation that makes you, you. That's exactly right. I mean, like to take a sort of the simplest example I can think of is

you know, race in this country is tied up with skin color, obviously. Well, skin color is this amazing trait that is, it's a natural sunblock. The pigment in your skin that gives, that makes it darker is melanin. It's this wonderful natural sunblock. It's this really cool evolutionary story. People, you know, populations in high ultraviolet light intensity areas make more melanin in their skin. Those alleles have been, you know,

more successful. And so, you know, you get darker skin in high sunlight areas, less, you know, lighter skin in low UV areas. But just because I know about that trait, I don't know anything else about you necessarily. I don't know anything about your cardiovascular health risk or anything, other systems. So these systems all vary independently. And when I categorize and say, oh,

yeah, you're white. Oh, you're black. Oh, you're Asian. And therefore, I think I know everything else about you. You don't. You don't. And that's an important kind of way to sort of think about human diversity, I think. I'm smiling because you give a really easy example of skin color in the book. Another one from my sector that you give

is related to kidney. Oh, yeah. So GFR, right? Now, a little, I'll set some background for you and then you can walk through. If you get any blood work done, a very common blood test you'll get

Even if you don't have any kidney dysfunction, it's called glomular filtration rate, right? It's actually an estimate of a measure. What it is, is it's a blood test that measures how effective your kidneys are filtering and functioning, right? But it's actually not a kidney test directly. It's a blood test, right? Okay. EGFR is how you're going to see this. It's on almost every blood test you've ever had done. What you'll also see is you'll generally get two numbers. You'll get a number that says, are you

African-American or you're not African-American, right? Or you'll actually have to answer that question prior to your blood draw, and then they'll give you your response based on what you answered. You look on your blood work at home right now, you'll see that in there in one form or fashion. Why is that done? And is that accurate? Is that a good way to think about what do we know about? Why is it done, first of all? It's the only metric I know of

in blood work from just the standard one that is broken up by that. Yeah. So give us, I don't really care about kidney function. You don't care about it, but this is highlighting this bigger point. Yeah. It's the way we think about how bodies work fundamentally and then about how bodies work differently and why, and how we think about human diversity. It has, I believe there was an old study in the sixties or seventies or something like that, that looked at GFR and

And they just happened to note, are the people that we're looking at, are they African-American or are they white? And they came up with a sort of predictive equation about how to get to your GFR based on your blood work. And they did it in two ways, one with and without. They did it for the white participants and for the black participants separately.

And that has carried on to today, to 2025, where if you get your blood work done, if you're African-American, you will get the black equation used to calculate your EGFR. And if you are white, you'll get the white equation used to do your EGFR. And there is no reason to ever think that the amount of melanin in your skin has anything to do with how well your kidneys function.

Those are unrelated traits. But because we think about diversity in these sort of group based ways, you know, we have these sort of funny hangovers of thinking about diversity in the wrong way. In this specific example, why does it matter that we're doing that? Well, because the same blood work from a white patient and a black patient will give you two answers.

And it could be that one person gets flagged as having kidney problems and the other person gets flagged as being perfectly healthy. With the exact same number. With the exact same blood work number.

And that's a real problem, obviously. And it's not just kidney function. Equations used today in medicine to estimate bone health, to estimate your risk, you know, if you have had a cesarean section in a previous delivery and you want to have a vaginal birth in the second one, your risks of that are race-based. That has nothing to do with your physiology. It is purely... Diabetes. Thank you. Exactly. There's so many of these. And...

We know that it comes down to fundamentally that even doctors who we trust with understanding our physiology the best and being able to give us the most individualized, bespoke treatment still don't have a great way of thinking about diversity or are given these sort of legacy ways of thinking about diversity that we know are wrong. Would it be fair to summarize your position here? And Duke, please correct me if I'm a little bit even slightly off on this particular topic as well.

It's not that there isn't differences. There potentially could be differences in this small example with something like GFR and black and white Americans. There could be, but it's simply the fact that that's all founded right now on far less scientific evidence than you would assume. Is that a fair characterization? That's fair, and I think I would expand it, and I would say, first of all, we know that there are not—

If we look at human genetics across the globe, we do not find delineations, boundaries around what we in the U.S. are brought up thinking about as racial groups. There is no...

African and white, you know, black and white genetic gene pool. That's not how it works. First of all, any two populations around the globe actually share almost all of their variants, right? So any two people might be quite different, but if I look at the total number of variants, gene variants in this population, I'll find 90 plus percent of those same variants in another population. Pick any two in the whole, across the world. Any two communities. Any two communities. Within Africa,

genetic diversity is huge. And so there's no such thing as

an African-American genetic, that's not a thing, right? That's not a coherent group. There's actually more genetic diversity within Africa across populations than there is in any other part of the world because we're an African species. We've been there the longest. So, yeah, I think, you know, the way that we kind of divide things up by groups is inherently problematic. It doesn't have a scientific basis. And yet it shows up in these, what we think of as scientific things like the measurement of kidney function or the measurement of diabetes risk.

You said it earlier and you wrote it in the book that there are many other things to discuss in terms of diversity and culture and our history. And that is all true. What we're trying to do right now is just leave that aside and talk about the biology. Yeah. What you're saying again is there's not any lack of differences. We're all the exact same. That's not what you're saying. It is this different context of that. It's probably being extended into some areas where, again, the scientific support isn't as sound as you think.

genetics is another great example of that. So I want to go further into that because you just brought that up. First of all, you've got something like 20,000 genes and 3 billion A's, T's, C's, and G's in your genome, right? So we'll call that your genome. If we compare mine and yours and anybody else here in LA, LA is a great example because it's super diverse. Yep.

We'll find differences between any two people, but they're tiny, actually. Any two people, if we count all the AST season Gs, will be 99.9% similar. That's right. I covered this in season one in the genetics episode, but it really is hard for people to understand. Humans, for the most part, all have the exact same genes.

Yes, that's right. So you've got 20,000 genes and actually you've got two copies because you get one set from mom, one set from dad. And if I made a list of all your genes, you're, you know, the gene that gives you your blood type, the gene that, you know, et cetera, et cetera, all the way down the line.

you and I have the same set. That's right. And you and I and you and else and anybody else on the planet all have the same set. Now, we might have different variations. So the way I think about it is, you know, we're all, I'm wearing a shirt, underwear, pair of pants, shoes and socks, just like you. So we've made a list of all our clothing to be the same list.

But obviously your shirt's different than my shirt, your shoes are different than mine. So different variations. Great example. Yeah. So genes are like that. 20,000 of the same items, but different variations of those. Yep. And those variations come from those ATCs, things like that, right? Yep. Slightly different order. That's what we call a polymorphism or a variant or a mutation or... Yeah, perfect. Exactly. We can think about diversity then as what versions of the genes do you have?

Or how similar is the actual sequence of A's, T's, C's, and G's? Right? That could be a different thing. Because if you could have a gene that might be, genes are about like a thousand base pairs long. That would be a short one. Yeah. And you could have one letter difference. And so, between the two variants. And so those variants are 99.99 whatever percent the same, even though they're two different variants. Right. Yep.

And that functionally means that that gene will then produce a different protein or a protein that functions differently. And that's why your eyes are blue and mine were purple or whatever the case is, right? Exactly, exactly, exactly. Right, so any two people on the planet, the letters are 99.99% the same. And that's when we talk about us versus chimps, for example, that's what we're talking about, that kind of diversity. Now let's talk just about humans. And let's think about those 20,000 genes and the versions you have. Within any population, right?

You can ask, oh, what kind of, how many different versions of the blood type gene does that population, what will we find if we do a survey? And so, oh, I see people with type A blood and type B blood and type O blood, right? Those are all different versions of the blood type gene for that protein. If I look here in this small population, I go across the globe, I'll find the same variants, the same A, Bs and Os, maybe at slightly different frequencies, but I'll find them.

And so, you know, even though one person might be in that population might be type A, another person's type B. So those people are quite different. But actually, this population with As, Bs, and Os is similar to this population over here with As, Bs, and Os. So the population, it's a funny thing. Populations are more similar because they have the same variants than any two individuals are within that group.

If you can wrap your head around that, you can finally, that's the starting point to wrapping your head around human diversity. Because within any population, people will vary more than populations will vary on average. Right. Across each other. Right. If I were to get a commercial direct-to-consumer genetics test, and it tells me I'm 43% Scandinavian, 20% Mongolian, 6% Norwegian, whatever. Yeah.

How is that actually working? Is it even accurate? How are we deciding those numbers? Yeah, that's a really important question. And so you have 20,000 genes in your DNA, but between those genes are lots of stretches of DNA that as far as we can tell don't do anything. And because of that, you don't have evolutionary pressures keeping them the same. They tend to vary more. And they vary in a random way. And so they create noise, let's say, in your genome.

Now, the random processes that create noises in one population are unlikely to be the same as they happen in another population. So those random, meaningless bits of noise in your genome actually become a nice fingerprint for where your recent ancestry is. Because the same random things that happened in Scandinavia probably didn't happen in Southeast Asia.

And so that's what a company, a retail genetics company is doing. They're looking for those kind of meaningless, actually, the more meaningless, the better. Yeah, the non-coding stuff, right? The non-coding stuff. And so, yeah, so that's funny because I think those tests are, I think, are really fun to play with. They give you the sense that those genetic differences are big and meaningful when, in fact, the reason they work is that they're not meaningful. By definition. Yeah. We don't yet know that they're doing anything. Exactly. Yeah, that's right.

How do we distinguish, though? How do we draw that line? When you said recent ancestors. Well, that's another thing. So we know now that, you know, people have been mixing and moving globally forever. So there are no, you know, sort of genetically isolated pure populations. And everybody intermixes with everybody. That is just the truth. And so...

I couldn't use, for example, I would have a hard time, let's say it this way, those little random noise signals that tell me I'm from Scandinavia or Southeast Asia, those only work because recently we measured a bunch of people from those places and we know what that noise looks like there. But check back in in 100 years and it might be different, right? Because it's going to keep on churning. This churn is going to keep on happening. It's been happening for 200,000 years and that's going to keep on sort of mixing it up. How good would you...

our current database of genetics across the variety of cultures? We know it's hugely uneven, right? The most data we have in terms of, you know, UK Biobank or GenBank or any of these big databases, or for that matter, the retail space of, you know, those are all wealthy, largely white people.

in countries. Not entirely. There's, you know, there's fair, people work very hard to get coverage as far as everywhere they can get it, but just in terms of the bulk of the numbers. Yeah. I think the more recent data suggests that still to this point, 90 plus percent of genetic data is on

White Caucasian. That's right. That's right. And what we know is that when we go, we can talk about this next, when we do a study of, you know, what gene variants predict height. I would love for you to go into this. Yes, please do. Yeah. What gene variants predict height? What gene variants predict cardiovascular risk, disease risk? What gene variants predict, pick your trait. When those studies are done in the UK biobank with a largely white population, it turns out they're not what they call portable.

I can find those same gene variants anywhere else because, again, populations share these variants. But it turns out they're not predictive over there anymore. Oops. Right. And so, yeah, it's an interesting time to be alive, right? Because I remember in the 90s as an undergraduate, the human genome hadn't been published yet. Right. We were in the kind of the late stages of this reckoning about racial diversity and the fact that race is a cultural construct. Right.

that has, of course, important biology embedded in it. And actually, racism itself can create biologies. I mean, so there's a whole... But we understood that race is not a biological category. It's a cultural category. We understood it was a reckoning about sex differences. We were reckoning all these things. And we were ready. I think we were poised to do the next thing, which is to get down to the genetic level. And then we had the human genome published, and we're still...

It has a promise unfulfilled because the genome work has gone in a kind of a different direction. I think we still don't really reckon with diversity in the ways that we probably ought to. Well, you can explain a lot of things here, but one thing of note is

is I don't think many people have really gotten past or the awareness has gotten out about what I call the one-to-one gene fallacy, which is the entire human genome, the promise of it, the direct or indirect, was that we will sequence every human gene and because one gene equals one physical trait, we'll then know everything about you. That's exactly right. Yes, that's a great way to go with it too because the promise was I'm going to be able to sequence your genome and I'm going to know everything about you.

And it didn't happen. And now we know that it will never happen. It won't happen. The numbers are astronomical. They're astronomical. And environment has too big of a role. Right. You know, in a lot of traits, it has a very dominant role. And in every trait, it has some role. And so it's, you know, it isn't that you have three genes and the versions you have of those determine how tall you get.

there are at least 10,000 genes for which we know if you have variant A or variant B, you're going to be a little bit taller, a little bit shorter. And you add up all those over 10,000, and I might know something about your height, but then I also have to know your environment because I only know about half the story with the genetics, right? So it's a complicated system. Well, if we want to be predictive about things, we can understand it at a kind of broader level and just say, look, we have to understand the interplay of environment and genetics and

for each trait individually, how they work, that's the better way in to understanding why your physiology is different than mine or why this athlete is struggling with this thing or this person is struggling with that disease risk or whatever it is. When we want to understand our diversity, we have to break it down, I think, back to that kind of fundamental beginning and then it's a good way into it. Why does this stuff even help? Why does it even matter that...

We're thinking about genetics as an example wrong. We gave the example earlier of why it mattered for GFR. But can you think of any examples of where overgeneralizing by population or perhaps maybe

not thinking about the uniqueness of that individual population appropriately matters. Like, what are the practical implications of these mistakes outside of sociocultural? Here's a fun example, and we can do a couple of these, but here's a fun one. I was working in northern Kenya when we first started working on that project with a community called the Dasnich. This is traditional. Oh, perfect. Great, great. Traditional pastoralists, these folks, you know, they live with their herds, goats and cattle and camels.

And we started this project. We got into the community. And of course, it's community-based work. We met with community leaders. We met with the health clinic folks. We wanted to, before we started, to make sure we were talking to everybody and get everybody on board. And this is something we all wanted to do.

One of the folks we talked to was this German charity that was there to try to reduce malnutrition in this group. And so they're giving food supplementation to moms with little kids to try to fix what they saw as malnutrition. And so we met with this guy from the German charity, me and my Kenyan colleague, Rosemary, who's wonderful. And, you know, this guy's like, look, man, it's really bad.

malnutrition, 60% of the kids here are malnourished. That's scary. Obviously, that's a tragedy. And so we thought, oh, gosh, okay, that's important to know. And then, but you go out into the community, you go around the villages, and that's not what you see. What you see is kids running around, playing, happy, laughing,

And if malnourishment, you know, if undernourishment is that big of an issue, you should also see issues with fertility. You don't see that. You see big families. Folks are active, healthy, doing their thing. That's strange. How do we square the circle on that? And it turns out, you know, we're talking to the health clinic about this.

And they had in their records, partly with this charity, they had been doing this. They had been collecting heights and weights for children in that community, the Dostoevsk community for years and years. And they had hundreds, I think a couple thousand of measurements of, of, of kids heights and weights from birth up through, you know, up through childhood. Science gold. Wonderful. It's so awesome, right? Everything you could ever hope for. Yeah. So what we were able to do is basically make a Dostoevsk community growth curve, right? Yeah.

What the Germans guys have been doing is they've been taking heights and weights of kids and they've been plotting them against WHO standards. Oh, there you go. There you go. Right? Yep. And the assumption there is that kids everywhere across the globe all grow exactly the same. Bingo. The kids in the dodges community were doing a really cool thing, actually. They would start off normal height and weight. They would kind of fall off the growth curve a little bit around year one. But then around year two, their heights would shoot up. They were taller than the global standard, actually.

But because of that, their weight for their height, that ratio looked thin. Way off, yeah. Did they physically look ill? They don't look ill, but even the folks, they're just tall and thin. It's just the body build in that population. And so the German charity, they had their hearts in the right place. They wanted to help, but you are never going to get those kids to look like, you know, WHO standard kids because they are in that population and

And that's, you know, the alleles that promote a tall, thin build are really common. That's an adaptation in that part of the world for dealing with really hot climates. It's incredibly hot there. You're on the equator.

Being tall and thin is a way to be able to thermoregulate better. That's been known for a long time. We see that around the world. Tall, thin body build tends to be more common in really hot climates because it's a way to dump heat. Yeah, surface area. Surface area, exactly. And so these kids were doing exactly what their bodies were built to do. Now, if you understand the way that height works, just to pick a trait, and the interplay of genetics and environment, right?

then you can look at that and say, oh, that's the system. Now I understand it. Now, actually, now that you have a Dostoevsky-specific growth curve, now you can pick the kids that really do need help. Oh, yeah. That's great. You can help them. You can focus the help better. And I don't fault the German charity for wanting to help. Clearly. But they were never going to achieve. They actually left. They closed up shop and left because they thought we can't solve this problem. Oh, no. So there's a great example. If you don't understand how the system works,

You're going to make, you're going to come to wrong conclusions about how to help. You're going to come to wrong conclusions about what's going on. You're going to flag the wrong people for needing help. You're going to miss who does need help. You know, all these things. So I think pragmatically understanding how these systems work and how genes and environment work together and how it's a, you know, it's a trait by trait thing, you know, just because I know about their growth curves doesn't mean I know about anything else about them, by the way. I don't know their heart health or their mental health or anything like that. Those are different traits.

There is clearly need and value in population level research. This is, again, your field, at least your old field on that. What you're clearly arguing for though here, at least as I interpret it, is a move closer towards precision. Yeah. Individualized. Individualized, right? Yeah. How do we, in your words, square that circle? In other words, how do we set up research? How do we think about research on the population level? Mm-hmm.

Because there are benefits we can get from that that we can't get from, you know, individualized single research. Yeah, yeah, yeah. How do we get the best out of both? How do we use population level research so that we can be the most informed and then also not make these mistakes like we are currently doing with basically everything in genetics in terms of, to be clear, what I'm saying there is if you're making nutrition or exercise decisions based on

Your genetic testing. Yeah. I think you've laid out a compelling argument that that's probably quite short-sighted. Yeah. To be kind. Yeah. How do we do this? How do we think about it? What I think this kind of work argues for is a few different things. First of all, I think if we had better fluency, I think if you learned your biology and how these things worked,

In the same way that you learn social studies and, you know, English lit and all these things. I think that this is part of the general fluency that we expect kids to come out of high schools with or out of colleges with. That we would all be better consumers of things like retail genetics. We'd all be better patients with our doctors because when they say, here's how your kidney function looks, you'd say, wait a second. Right? Right.

So I think that's part of what this kind of new understanding of diversity and how our bodies work. I think that's one, you know, important avenue for that. In terms of how we change the way we think about research, here's what I would love to have. I would love to see research that didn't just reiterate the same kind of

wrong classifications like we think, right? I mean, I can tell you if you do NIH-based research, you're supposed to tell them how many Hispanic, non-white, non-black Hispanic, non-Hispanic whites, this is the census categories, right? And then somehow those categories are used to interpret results of your population-based data in a way that we know going into it is fundamentally problematic. And, you know,

I'm not saying that we don't want to have diverse cohorts. I'm saying the opposite, actually. Okay, thank you. Yes, I'm saying the opposite. I'm saying that let's take these individual by individual. If...

And let's look at trait specific, you know, let's look at trait specific physiology. Let's look at those individual axes of variation. It might be helpful to know in your big population that folks who are Black in the United States have these physiological outcomes. But that's not telling you that skin color does that or that their genetics did that. That's flagging that perhaps their environments, because of, you know, all the cultural baggage we have in the U.S., are

are affecting physiologies that way. Let's understand it that way. So we need diverse research. We need diverse research populations. But the way that we handle it just has to be different. Yeah, actually, I love how you frame that. If I could throw a little bit of an analogy on the spot here on that, the way that I generally like to think about population-based data, and let's just keep using that example. One trait that you'll see pop up, we said earlier, for Black African-American population

much higher rates of type 2 diabetes, much generally higher rates of obesity, right? So what you're saying is population data can shine a light on that. Yeah. And that allows us to say, hey, we need more focus. We need more emphasis. We need more resources. Yeah. Does that

then tell you if you're black, there's something in your physiology that makes you have more diabetes. Maybe, maybe not. All it's simply saying is there's something in the entire picture. Yeah, that's a great example. Another one is heart disease, hypertension and heart disease. We know that black folks, Native Americans, other minorities have higher rates of hypertension and heart disease than whites in the U.S. We know that. For a long time in the 80s, 90s,

Particularly the observation that we had higher rates of hypertension among black Americans was taken to somehow mean interpreted as they have a genetic predisposition to hypertension. I spent my graduate work in Memphis. Yeah. In health science. I had to teach this. And it's wrong. Yeah. Right. It is both true that that's that in the U.S.,

You know, black populations have higher rates of hypertension. It is also true that if you go anywhere else that doesn't have a history of racism, guess what? Yeah, they don't. And it's same with Native Americans have higher rates of cardiovascular disease in the U.S. Go to places where the healthiest hearts in the world are in indigenous populations in Bolivia.

Right? So, and it's basically a very similar, you know, recent diaspora of those populations down into South America. So you're talking about genetically kind of similar populations if you want to talk about it that way. Right. So...

Point being, we take the wrong conclusions, we make the wrong fixes, we learn the wrong lessons when we don't understand how our bodies work and why we become unique. And to your point of the German charity, this can be done well-hearted. Yeah. Right? It's just not...

Again, potentially not focusing the right lens and help and support in the areas because we don't understand what the actual rationale, what the reason, what the cause is for some of these issues. So on the topic then of diversity and physiology, we'll stick again to our side of the equation. How do we best think about that? What is the best way we can learn from it, make progress?

better help, better support, whether it's scientifically, public health. I know you don't work in areas of public health, but what is the most appropriate way that we should maybe start thinking about it or advocating for types of science, like anything that's the solution side of the equation, how should we be better thinking about it? Yeah, I think when we understand the role of environment, especially in a lot of these health outcome, diabetes risk, obesity risk, heart disease risk,

And I think a kind of individualized approach and a life course approach, because we're thinking about environment over the lifespan here, points us to research that's going to focus on early life experiences, especially getting those environments right. Right. Childhood is a really important, obviously, learning period for your body's physiology. And, you know, I think.

Using, you know, when we see differences among different communities in health outcomes, not ascribing that to some inherent issue there, but flagging that as usually when it's at the population level, an environmental issue. When we see individual differences, well, now we can ask, okay, what is it about your individual physiology that we need to tweak? That's a move towards, you know, kind of precision medicine that I don't think exists.

You know, I don't have all the answers there yet. I don't know that anybody does. But that's, we can focus more on the individual that way and hopefully do a better job. It's again, I'll never get over this interesting, what I feel like is a juxtaposition of what your academic background is and the fact that you're now arguing so heavily for

I'm sure it feels like it's seamless and it is the same thing, but I'm like, finally, yes, a person that's telling us all about how we can learn from studying one tribe a thousand years ago is now getting in here. Do you feel like your time as, I don't know, were you technically an EMT? I know you were in that stuff. That's right. Yeah, about three or four years. Yeah. Yeah.

Is that a part of this here? Is that why you're seeing this? Is that how you're able to kind of zoom back and look at population level stuff as well as the individual person? Yeah. I feel like when I read that, when I knew that about you, I'm like, this has got to be in there somewhere that's driving this situation. I think that my time as an EMT was motivated by two big things. You know, you never know. We tell our stories about why we do things after the fact. Yeah. Right? Yeah.

so I don't know if I would have articulated this as an 18 or 19 year old taking that EMT class at Penn State, but I learned how to do this stuff. I think it really hit two buttons for me. One was the human physiology side and just seeing, you know, medical, the medical world play out, you know, in practical terms with a patient that you're taking care of and understanding the body that way. That was super cool. Yeah. But the other thing was, you know,

And medicine, and especially emergency medicine, happens behind closed doors for most of us. We don't get to see it firsthand. Certainly as growing up, I didn't get to see it. My parents weren't doctors or anything like that. And so to kind of pull the curtain to the side and understand how that high-intensity world worked and just understand how the world worked a little bit, and that was...

a draw I couldn't, I think that was the biggest draw. I wanted to know what happened to the back of the ambulance, man. Yeah. You know, I wanted to know what happens when you pull up on a car wreck and you have to make decisions right now about how you're going to treat the patient, keep the scene safe, get the, you know, and, and the immediacy of it, the fact that it's something that most of the, that I never got to see growing up, um,

Yeah, that was the draw. And, you know, the patient care, obviously, and that's obviously a big thing too, but I think that was the big draw for me. Did you have a love of physiology before that or was that what jumped it off a lot? I think...

That and the anthropology classes I was taking were very kind of biologically focused. So that combined elements of that. You know, what you're learning from the medical context in an EMT book and then the evolutionary perspective on it in my classes, I think that...

I hadn't really put it together like that before, but I think that's right. I think that's kind of was this cool synergy as I was figuring out what I wanted to do with my life. What do you have coming up next in that? You were talking earlier about some of the projects you got going on. Where is the next...

question. We talked about a bunch of things you could answer. What's on the immediate horizon for you right now? What are you most interested in next? Well, we have a really exciting project happening right now, two actually, trying to understand metabolic ceilings. Is there really a cap on what the body can do? And if there is,

How do we push it? What happens when you push it? And so we've got one study going on right now looking at pregnancy and looking at female athletes through pregnancy that are maintaining really high activity workloads to sort of see how that pushes the body around and energy expenditures and all the follow-on things that happen with that. That's a super exciting project that hopefully we'll have out in the next year or so.

We have a project looking at ultramarathon runners, asking outside of the pregnancy context, just people who are just pushing their bodies to the extreme, what does that look like physiologically, metabolically? And that's work where I'm doing with Drew Best in Massachusetts. And that's been really fun. So those are kind of that avenue of research.

We want to get work going, trying to look at organ metabolic rates and how those might juggle and change in the face of lifestyle change, in the face of different interventions. That's really early days, and I'm hoping to get that going. We'd love to know, in that same kind of distant horizon is looking at life course changes in childhood and old age, how metabolic rates change.

And then, you know, we have a bunch of projects right now looking at, in different communities, we have one looking at health, cardiometabolic health in pastures, in clergy in Western North Carolina. You know, there's a...

They have a we were asked to help out on this grant. There's a kind of higher rates of cardiometabolic disease, diabetes and stuff with this population that we'd like to see. Higher than sort of background. Other folks in the same communities. We want to understand what it is. What is it about the challenges of that job? Psychological, physical activity, diet that are pushing, you know,

health outcomes where we don't want to see them. And we're working abroad still. So we have the work in Kenya, other collaborations around the world. So yeah, you know, it's a busy, it's a full plate. Yeah. You're not slowing down at all. In addition to writing books and all those things. If someone would have been as fascinated as I am in this conversation, I really, really thoroughly enjoyed it. And they're thinking to themselves, okay, great.

How can I better think about metabolism, energy expenditure, all these things? Is there any other lessons that you think people should glean that you really want to emphasize or that they can pull from? You mentioned this several times now. You're a natural teacher, just talent-wise, and you also clearly have a passion for it. So how do we help connect this last dot for people in saying, like, I'd really like for people to learn? Yeah.

Okay, so let's start with the metabolism thing. If people are trying to optimize their health, change their body composition, maybe maintain their body composition, thinking about metabolism, I emphasize that we should think about diet and exercise as two different tools for two different jobs. Sure, there's lots of crossover, but diet's going to be your best tool for maintaining weight or getting your weight where you need it to be.

exercise is going to be your main tool for everything else, right? Heart health, mental health, muscle health. Fill in the blanks. Now, how do we connect that to this second half of our conversation about individualized approaches and diversity? I think

You need to treat yourself as N of one and understand that there is a real broad range of possible diets that might work best for you, possible exercises that you're going to get into that you're going to love more or less, you know, your individual environment and genes, how those mesh together. That's nobody has that same setup. You know, you are unique.

And so I think the one size fits all approach is I think kind of evangelistic. You have to have this diet approach kind of thing. Give yourself a break. Walk away from that and just ask, OK, I'm going to pay attention to myself and I'm going to treat myself as N of one because you are. And you can play around with what we know is out there. Be evidence based, you know, read, read good books, read good papers or listen to great podcasts.

And figure out what the evidence is out there and then say, okay, I can play with this without putting myself in a bucket of, oh, I'm a woman and therefore this. I'm a man and therefore that. I'm this group or that group. I'm that group. You're out of one. So, you know, go out and feel free to sort of play with it that way. And, you know, I think with that kind of an approach, first of all, it lets you breathe a little bit and have a little less stress about, oh, I'm not doing it right.

Perfect, right. It's empowering. It should be more empowering than not, right? Yeah. And then it also lets you explore and find something that you love. I'm an anthropologist. I study people. And what I can tell you is across the world, around the world, if people don't love something, it doesn't matter what, culturally, whatever, all the diversity, if people don't love something, they're not going to stick with it. People do what they love. They always fall back to it.

And so if you can't find a lifestyle approach that is going to really resonate with you, it's not going to matter what it does physiologically because it's not going to stick. So I think that's, you know,

Listen to yourself and be N of one because that's what you are. If somebody wanted to do something like this and they wanted to start learning more about their metabolism and figuring out their daily energy expenditure and things like that, what tools would you recommend? Where should they start? What options do people have if they want to follow your advice there? Yeah. Well, I mean, you can go low tech. You've got the bathroom scale. Yep. Right? Always the best place. It's not a bad place to start. You know, if you're... And...

You know, we talked a little bit in this conversation about models versus data. If your model is I'm on this diet and I'm eating at an energy deficit, but the data say you're not losing weight, then I'm sorry, you're not eating. I mean, you know, that's just it. And so you got to kind of move your, follow the data, not the model. You know, there are lots of companies out there that will measure different aspects of your health if you're into that.

I would, if you want to measure your energy expenditures, I'm a science advisor for a company called Colorify. You can check them out and do that. Tell us a little quickly about what that is and how it works. Oh, right. Yeah. So this is a really cool company. And full disclosure, I've used it many times. I've

I paid for it full price, no discount. So I've used it quite often. Awesome. Yeah. Yeah. So this is a company that was – so the technique I talked about earlier about how we measure total energy expenditures, all the calories you burn per 24 hours, the technique we use is called the doubly labeled water method. It's an isotope tracking method. And it's the gold standard for doing those kinds of measurements. Okay.

And until recently, there wasn't sort of a retail way to do that. You couldn't just get a measurement for yourself. You had to sign up for a study or something like that. Hari Mix, who's the founder of Colorify, and I was there too to help get it off the ground. I'm a science advisor for that company, full disclosure. They wanted to make this sort of available to everybody. And so you can check out Colorify and get those measurements yourself if you want. Great. Fantastic.

What would you say to somebody who was concerned that they've been in a caloric deficit for a long time? They have been potentially, whether they're losing weight or not, but they're eating a really low amount of calories. Potentially they've lowered it. Yeah. They're weighing, they're measuring, they're reasonably accurate in that. And they've continued to reduce a couple of hundred calories. It's been months and months and months. Now they're concerned that they have crashed their metabolism. They've- Yeah.

Gone to the bottom. People will explain this differently, but is that a real thing? And if so, what's happening there? You can definitely see people's like basal metabolic rates get lower when they go on really, you know, kind of crash diet kind of things. Yeah.

As far as I know, I don't know of any evidence that says it doesn't just recover when you kind of go back to a more normal amount of food and a more normal exercise load. And so I don't think anybody is sort of forever damaged from whatever they tried in the past. You know, yeah. So, again, let yourself off the hook a little bit and it's going to be OK. Yeah. I really, really appreciate you coming halfway across, well, entirely across the country. Yeah.

And I didn't run. I took an airplane. You did. Yeah, I didn't do the marathon a day thing for five months. I just jumped on a plane. I cheated. I'm not going to lie. I feel like that's a little bit lazy. It is. I mean, that's fair. That's fair. You got out of here, but really appreciate it. I thoroughly enjoyed it. I've been waiting a long time for it. I know people are going to get...

a ton out of this um if people want to follow along with your journey and support and stuff where can they do those things uh you know we're online you can check out the poncer lab and we try to uh you know update how our projects are going um of course we publish everything in the scientific literature which isn't always easy to keep up with but it's there

And then, you know, check out – I guess you could check out my writing. We've got a new book coming out, and I'm sure there'll be more fun stuff to tell the world about. And then the foundation as well? Oh, thanks for that. Yeah. One of the things that we've done working with the Hadza community is to start a charity that helps support their population health to kind of give back because we've learned so much from them. Yeah.

We want to make sure we're giving back. And so it's called Hadza Fund, H-A-D-Z-A-F-U-N-D.org. And if folks want to support the Hadza community, keep them strong and healthy, they can go on there and make a donation. It's always appreciated. Really appreciate you coming out. I learned a ton. I know people are going to respond really positively to this. So thank you so much. You bet. Thanks for the invitation. It was a really fun conversation.

Thank you for joining for today's episode. To learn more about Herman, follow along with his books, social media, laboratory, and other resources, please check the show notes for direct links. Thank you for joining for today's episode. My goal, as always, is to share exciting scientific insights that help you perform at your best. If the show resonates with you and you want to help ensure this information remains free and accessible to anyone in the world, there are a few ways that you can support.

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