Recap: The power of a 12 hour eating window | Prof. Satchin Panda
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Hello and welcome to Zoe Recap, where each week we find the best bits from one of our podcast episodes to help you improve your health. Today we're exploring the power of a restricted eating window. Do you enjoy a late night snack? A little nibble or drink after dinner but before bed? If so, you're not alone. Many of us indulge in this habit. After all, it's just a small tree, so it couldn't possibly have a big impact on our health, right? Well, a growing body of research suggests otherwise.

That seemingly harmless snack could be disrupting your eating window and preventing your organs from functioning at their best. In this episode, Dr. Sachin Panda joined me to discuss the science behind time-restricted eating and how it interacts with our body's natural circadian rhythm. What does all this circadian rhythm tell us about when we should eat?

So there are two fundamental discoveries about what resets or synchronizes our circadian rhythms. One is light, the daylight or light that is rich in blue light.

that goes through our eyes and resets our brain clock and resets when we sleep, when we wake up. So that's light is one cue. But the other cue is when we eat. If we eat at the wrong time, like one night if you're eating very late into the night, then that night your body clock gets confused thinking, huh, was it a delayed dinner or was it an early breakfast?

And for the next few days, it gets confused. So all the body clock, the clocks in the liver, gut, heart, kidney, all of those clocks get disrupted. So they can't work pretty well. So just a late night can mess up all, and it's not even just my gut. It can even mess up my, you know,

my liver or my heart. That doesn't sound good as someone who has a tendency to maybe have that little snack before bedtime. Yeah, because your body is thinking, well, was it evening? Was it a long, was it a late dinner? So after we learned this, then the question was, well, we know that having a strong circadian clock is good for health.

In modern life, it's very hard to control light exposure because from morning till night and also late into the night until we close our eyes, we're always exposed to light. It's very difficult to control that. But can we control when we eat? And just by when we eat, can we change health? So, you know, what is now popular as time-restricted eating or intermittent, very popular form of intermittent fasting is

It was not there 12 years ago. So my lab was the first one to do this experiment in mice, just like all basic scientists do, because we can control the experiment pretty well, and we can also do molecular analysis. So we took a few groups of young mice, and they were identical in genes. They were born from the same parents, grew up in the same room.

They had the same microbiome. They ate the same number of calories from the same food. The food we gave them was relatively high in fat and carbohydrate, which would be equivalent to eating, say, fish and chips every day or a burger every day.

all the bad food you can think of. - Not the healthiest diet for a mouse or a human being. - We knew that when mice are given this kind of food and they're allowed to eat whatever they want to eat, they become very obese, diabetic, they have high risk for cardiovascular disease and also the increased risk for liver disease and cancer. This is from 100,000, sorry, 10,000 experiments that were done before we did the experiment.

And they get the same number of calories also, but the first group was allowed to eat whenever they want, and the second group was allowed to eat within an eight-hour window during nighttime when they're supposed to eat. Mice are night active, so we get the food

at nighttime. And within three days, these mice will learn that the food is available only for eight hours. So they eat the same number of calories within that eight hours as the mice that had access to food 24 hours. So very simple experiment. We monitor their food every single week to make sure that both groups are eating the same number of calories. And we weighed them every single week. And at the end of 18 weeks, there was this huge surprise that the

First group of mice that ate around the clock as expected. They were obese, diabetic. They had high cholesterol, liver disease. All the bad things happened to them. While the second group

A date within eight hours, surprisingly, miraculously, they were completely healthy. Which is crazy, right? You're saying they ate the same amount of food, the same type of food, and just by restricting their eating to eight hours, they managed to deal with this unhealthy diet, whereas the ones that could graze whenever...

ended up getting really obese. We repeated this experiment with three independent researchers in the lab who did not even overlap with each other to make sure that this is true. Because think about it, over the last 150 years of nutrition research, we know that

What we eat is important because we have to eat healthy diet. There is no doubt about it. How much we eat is also important because there is a rich literature of almost 100 years showing that reducing food intake

improves health and in many laboratory animals at least it increases longevity. And I think this is a fascinating discovery and you should feel really proud. Sachin, I would love to take this now, you know, for our listeners who's like you've painted this incredibly powerful picture of the mice.

But of course, none of our listeners are mice. I don't think any of our listeners are mice. So if you're a human being listening to this, and a number of our listeners will also have heard that mice studies don't always translate fully to human beings. What does the evidence say today? What would your advice be for someone who's saying, "Well, what does that mean about how long should I be not eating for during each day?"

Okay, so the first thing is what is actually considered food because a long time even for my mouse study I was not getting funding so the normal criticism I would get is well people eat three square meals within 10 to 12 hours so your findings have no human health implications. Then

We started looking into when people actually eat. And we know that we eat at different time on different days. And sometimes, just like we wake up late in the weekend, those who are working a normal day shift, they also wake up slightly later in the weekend. We also change our breakfast time. We change our dinner time. And to our surprise, until 2014, 2015, there was not even a single study that

objectively short, when people leave from one day to another for a complete one week. And we thought that, well, we have to do this experiment. So we had 156 people doing this for three weeks.

And we said, just take picture of everything, even glass of water, whatever you're doing. So we went through the pictures to make sure that we discount all the water and low calorie, non-caloric food. And what we found was less than 10% of people actually eat or drink all their energy containing food and beverages within 12 hours, punless. Less than 10% in your study? Yeah. And these people, none of them was a...

shift worker. These are all nine to five regular job people who do regular job or who are homemaker at home. And at the beginning of the study, we had actually asked them, when do you think you eat? And almost 90% of them had answered that they eat all that food within 12 hours.

So here's a disconnect between when people think they're eating versus when they're actually eating. We have about 150,000 people who are Zoe members now. And as part of this, they're locking their food. And we similarly see, firstly, there's a lot of variability, as you say. And secondly, that there's a lot of activity generally in the evening because it might be, I'm going to have...

I think I've finished my food, but then maybe I can have a glass of wine later in the evening, for example. Or, you know, I'm going to have a snack that I don't really think about because that's just like a snack. It's not planned. So what is your best view today about if someone's listening to this and saying, you know what?

I'm currently not eating all my food within even 12 hours. Sachin's saying this is really bad. What do you feel the data suggests at the moment that someone should be thinking about is the right way to manage their, you know, the duration when they should be eating and then fasting? Yeah, so what I say is almost anyone from 10-year-old to 100-year-old can and should eat all their food within a 12-hour week.

So whether you are healthy, unhealthy, you should be eating within 12 hours. The reason is even after your last meal, your stomach and the digestive system takes another five hours to digest that food completely, absorb all the nutrients. So although your mouth finished doing its job, your stomach is still working for extra four to five hours.

So only after four to five hours, it's getting a little bit of rest. So even if you are eating for 12 hours, your body is getting only seven hours of rest from food. Then the question is, well, if someone has high blood pressure or prediabetes, for example, or moderately high level of cholesterol, of many of these risk factors, then what can they do? So this is where

It becomes a little bit difficult because those who are headstrong and can eat everything within, say, six, eight, or nine hours, then...

they can do, and they might see a lot of benefits. And so far, what we are seeing is there are many studies, not only from our lab, from many other labs, when people reduce their eating window by three or more hours. So this is where it becomes a little tricky. So for example, if you are consistently eating from, say, six o'clock, you get up, and then by 6.30, you have your tea with cream and sugar or a biscuit or something else, and that

before going to bed at 9 o'clock or 8 o'clock, you have some snack, then it's already pretty big. So if you reduce your eating window by three or more hours, and it's not less than eight hours, so then you'll actually begin to see a lot of benefits. First thing is many people who do this, they say that within a couple of weeks, their sleep improves. They can sleep much better at night, and then next day they feel more energetic.

And then those who have a high blood sugar, blood pressure or cholesterol over three to six months, they do see improvement in at least one of these parameters. And Sachin, I've met some people who are saying, "Hey, I'm doing time-restricted eating. It's fantastic.

Therefore, I can sort of eat what I want within this period as long as I'm restricting the time. That's the key. Now, it's not going to surprise you that as Zoe, we're pretty skeptical about this. But what's your view? Can you solve your health problem with food?

with the time-restricted eating without changing what you eat? What we find is people actually do time-restricted eating or intermittent fasting and at the same time they improve their nutrition in interesting way.

So let's begin with what happens in real life. So those who are trying to do eight hours time-restricted eating or 10 hours time-restricted eating, they're going through 16 hours or 14 hours of fast over lunch. And after this long fast, when they're breaking the fast, they tend to eat a bigger breakfast because they're so hungry after 16 hours of fasting.

And typically breakfast is for many people, not for all. Breakfast is the healthiest meal of their day because that's when they have complete control of the food. They're at home, they can control what they eat.

And since most of us know that healthy food is good, so a healthy breakfast begins their day. And what we see is they also reduce snacking. So there is less snacking between breakfast and lunch and also between lunch and dinner. So in that way, they reduce their food intake from snacks, which are mostly not so nutritious food. Even if you are eating a protein bar that has a lot of sugar.

Then what happens is those who are finishing their eating before 8 p.m., whether 5, 6, 7 or 8, and since kitchen closed, the bar also closed, so they also reduce their alcohol intake. And this is what we specifically saw in one study with firefighter study. We saw that those who reported drinking alcohol at baseline at the beginning of the study

they significantly reduce their alcohol intake if they were in the time-restricted eating group. So these are different ways people actually inadvertently improve their nutrition. So you're saying often they combine the time-restricted eating actually not with making their diet worse, but making their diet better in part because it's like, well, I'm really hungry and I've got control because I've got my breakfast and also because I'm going to not eat a lot of these like bad snacks at bad times or whatever.

I know that this is still an area of very early research and it's something where Zoe is actually very involved as well because it's so interesting. Right now, you mentioned that almost everybody should be trying to restrict their eating to within 12 hours. What is your view about the added health benefit of restricting that to 10 or 8? So those who are...

Current eating habit is 12 hours. If they reduce it to eight hours, they will see benefit. And those who are, this current eating habit spreads over 14 or longer hours. If they reduce it to 10 hours, we also see health benefits. So the bottom line is if you can do eight hours, it's better. 10 hours is not that bad. And 12 hours you should do in maintenance more because

Once you're healthy and if you're athletic, if you're doing a lot of physical activity, or for example, those who had a baby recently who cannot fast for a very long time for obvious reasons, they can still try to eat within 12 hours. So that's why I say there is no single hard and fast rule. Brilliant. That's it for this week's recap. If you're hearing this, you're ready on your way to eating mindfully for better health.

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