The surprising health impact of eating too fast
21:42 Share

Hello and welcome to Zoë Shorts, the Bite Size podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolf and today I'm joined by Dr. Sarah Berry and today's subject is eating rate.

Which is really just a fancy way of saying how fast we eat our food. So does that have any impact on our health? Indeed it does, Jonathan, and there's a lot more to eating rate than just how it interacts with our weight. Quick, let's get into it then. Or should I say slow.

Tell us a bit more about eating right, Sarah. I don't know about you, Jonathan, but these days it seems like it's easier to gobble down our food rather than mindfully take our time with a meal. And this is probably because of the type of food that we're eating as well as the way we now live our lives.

Definitely. I think like half the time I'm now eating lunch while on a Zoom call during the week, or I'm sort of shoveling away some food while looking after the kids. That sounds familiar to me as well. And I think it's really an unfortunate reality of just how busy many people's lives are now. And

It's really not good for us. Essentially, your brain needs time to realize it's full. And studies have shown that it takes between five or even up to 20 minutes for your mind to catch up with your belly. And research also tells us that...

that eating more slowly increases the response of appetite-regulating hormones. So these are hormones that tell us how full or how hungry we are. And one study with children found that 42% of children whose parents reported that they ate quickly were also overweight. And these children were also more likely to show overeating behaviours according to what their parents reported. So in a nutshell, Sarah, you're saying eating faster makes it much easier for us to continue eating, even when we're not actually...

actually hungry anymore? I believe so. And interestingly, it seems that tendency to eat slowly might be something we inherit from our parents, partly from replicating their habits and partly due to the food choices that we make based on what our parents brought us up to eat. It makes sense that

Eating faster means taking in more energy and the research backs us up. In our Zoe Predict One study, we saw that faster eaters ate on average 120 calories more per day than the slow eaters. And other trials suggest that reducing your eating speed by around 20% can lead to a reduction in energy intake of around 15%.

Well, that all sounds a bit magical. And I have to say, Sarah, that always makes me very suspicious now after like six years of Zoe. So if I eat more slowly, will I really magically lose lots of weight? Okay, so there hasn't been loads of research on this. And I think this is what makes it really exciting to be a nutrition researcher at a time where we're only just really unraveling all of the evidence. But what has been shown is that

There is a link between eating rate and there is a link between the risk of developing obesity. So, for example, research from Singapore published in 2020 suggested that people who self-report a fast eating rate carried on average five kilograms more body weight than slow eaters. And they ate also on average an extra 105 calories per day.

The researchers also found that the fast eaters had a larger waist circumference by about three centimetres, which we know is really important in terms of our metabolic health. And fast eaters were also more likely to develop overweight and particularly abdominal weight. So this is the weight particularly around your

belly, which is linked to having more visceral fat, which is a type of fat that sits inside your abdominal walls and surrounds all of your organs. Now, this study wasn't a one-off though, Jonathan, and there has actually been lots of other studies that have shown an association between how

quickly you eat and excess body weight. Well, that is interesting and I would say surprising. I'm assuming that that then has plenty of knock-on effects for our overall health. If so, can you sort of take us through what that means for these different areas? Yeah, so the first major area is your cardiometabolic health.

health. So that's, you know, heart and blood vessels and also things like strokes and things like that, right, Sarah? Yeah, that's correct. And in 2017, a cardiologist from Hiroshima University in Japan studied more than a thousand people over five years to figure out the relationship between eating rate and something called metabolic syndrome. And I looked this up.

And metabolic syndrome is the name that researchers now like to use for five risk factors for things like heart disease and diabetes and stroke, which are obviously very serious. And those risk factors are apparently high blood pressure, high triglycerides, which I think we often call sort of blood fat, high blood sugar, low levels of good cholesterol, and finally a large waistline compared to average.

That's correct. And what they found was that the fast eaters were almost twice as likely to develop this metabolic syndrome. And a higher eating speed correlated with greater weight gain, correlated with higher blood sugar, higher levels of LDL cholesterol, which is our bad cholesterol, and also a larger waistline. And interestingly, Jonathan, a lot of these associations remained even after we accounted for

for changes in body weight. So even after we accounted for changes in body weight, we still found that fast eaters had higher blood sugar and higher levels of bad cholesterol. And so Sarah, it sounds like this is similar to what we found with our own ZOE predict study, where you were saying that eating rate is associated with energy intake, body weight, and this sort of cardio metabolic risk.

in that study, which was UK and US. Yeah, that's correct. And there's been other research that's been published as well that has drawn a link between eating faster and higher risk also of type 2 diabetes. And studies have shown that this may be because chewing more slowly stimulates more insulin release, which means better metabolism.

glucose control. And we think that this might be because if you chew for longer, you have more saliva uptake and this causes an earlier insulin and glucose release. Let me tell you a quick story. So Wednesday last week, I went for dinner with my wife, Justine. Now this would have been a source of anxiety for me in the past. And that's because some foods would leave me feeling really tired and sick for hours afterwards. And as a result, I actually followed quite a restrictive diet.

Then I did Zoe and discovered that I'm prone to blood sugar spikes. From my Zoe digital coach, I learned that this doesn't mean I have to restrict what I eat. I just have to be smarter about my food choices. So back to last week at the restaurant. We were eating Italian, which before Zoe would have left me feeling terrible. But my Zoe coach helped me make choices that consider my blood sugar. I started the meal with a delicious Italian salad and then enjoyed some pasta afterwards, drenched in olive oil, of course.

And after dinner, I felt great, energized by my food and by the fact that now I don't have to limit the foods I eat and choose between a healthy and a happy life. Whether I'm eating out or cooking, my ZOE Digital Coach helps me make smarter choices every day. Honestly, it's transformed how I feel. And according to the scientists who continue to develop the Digital Coach, making these choices now could give me many more healthy years.

Why not join more than 100,000 other people giving ZOE membership a shot? And tell me what you think. To take the first step towards the possibility of more energy, less hunger and more healthy years, take our quiz to help identify changes to your food choices that you could make right now. Simply go to zoe.com/podcast, where as a podcast listener, you can also get 10% off.

And what about digestive issues, Sarah? We do know that actually fast eaters do often report poor digestion and a study has shown that they may also get more acid reflux than slow eaters. So the overall message seems pretty clear, sort of slow down at the kitchen table. Yeah, I think...

the evidence shows, Jonathan, that it is going to be helpful on an individual basis. And there's lots of research exploring if this could be a good health and weight loss strategy for the population as a whole. Now, Sarah, pretty much everything you've described so far are really association studies. So they show people who put on weight were eating faster, but they don't prove the two are linked. So in other words, if one of those fast eaters switched to slow eating, it might not change anything, right?

The gold standard, I know in nutritional science because you talk about this all the time, is a randomized control trial to really prove that it's the eating speed that causes this rather than everything else. I know from many conversations with you and Tim and many others that

often there are these effects that are found in these sort of observational studies like this, where you study people over time. And then when you do a randomized control trial and you say, let's actually make people change their behavior, you know, often that disappears because maybe there's some compensating effects or the two, they would just happen to be linked, you know, like

if people aren't well, then they're not able to do lots of exercise. You see a much bigger impact of people who are doing exercise because you've already sort of removed all the people who were sick. Where are we on this in terms of eating rate? Yeah, so I think you're right, Jonathan, in saying a lot of the evidence is this association evidence. But what that does is it does give us as researchers that kind of first clue that something interesting is going on. And there have been a small number

of these interventional studies, particularly ones that point to interesting mechanisms. So, for example, even in our own ZOE data, we do see that if we look at fast eaters and slow eaters, those that are eating their meals fast do have

a higher glucose response compared to those that are eating their meals slow. And this is immediate real-time data that we're collecting. We also know from a study that was conducted in 54 teenagers, those who slowed down their eating rate, which was by waiting 30 seconds between each bite, which I think is quite hard to do, they lost a significant amount of weight after one year. And I think this is what we're

be really interesting to explore. And I really hope we can explore this in our Zoe Predict data. So in addition to this study with teenagers, another example of a study that found that when female volunteers slowed down their eating speed, they ate on average 60 fewer calories

Now, interestingly, they also felt more full than the people who were eating faster, who ate more calories. That is really interesting. So how do we change our eating rate in practice? I mean, is it as simple as saying sort of chew more slowly or do I need to wait 30 seconds between eating?

each bite? So I think it depends on what's easy for you. There are other ways too. So firstly, a study from China found that people cut their calorie intake by over 10% if they chewed their food 40 times instead of 15 times. This is because it had double the

benefit of allowing those appetite-regulating hormones that tell us how hungry we are or how full we are to kick in. And the saliva will begin this whole digestive process for you. But this can be quite tricky, I think, to chew 40 times every mouthful. So another tactic that I think might be a little bit more achievable for everyone is just to put your

cutlery down between each mouthful of food. So I don't know about you, Jonathan, but if I'm having a sociable meal or I'm out with friends deep in conversation, I eat a lot more slowly because I'm putting my cutlery down, taking part in that conversation and slowing down naturally the rate I'm eating that way. So I have to say the idea of on top of that, putting my cutlery down between each mouthful of food seems a bit crazy. So I do prefer some of the other tips that we found in our research. So one of them I thought, which

made a lot of sense to me is you might want to try not eating in front of screens when you're a lot more likely to be eating mindlessly and quickly and sort of shoveling it in and not thinking about it. Drink water during the meal. So that's sort of, that's a way to interrupt, right? Versus somebody who's just not drinking anything. Take smaller, uh,

bites and don't wait until you're completely famished to eat, which I thought was interesting because if you're completely famished, then you are sort of really shuffling this in. And the idea that you're doing good by waiting might actually be balanced out. So what about, I mean, all of this leads me to think about the texture of food. And I'm sort of assuming that

this can play a big role. And I think that naturally makes me start to think about how the texture of food is so transformed with today's sort of ultra processed food. Is there any science on this? So,

I think that the texture of food is actually really important when we consider the health effects of foods. And I think it's really important to consider now, given that over the last 50 years or so, the texture of much of our food has changed with all of the new processing techniques. And it's not something I think we give enough attention to. And interestingly, there was a recent study that was only published last year that looked at the relationship between eating rate and food texture, as well as the level of processing of the food. Now,

It has been argued by some people that part of the reason that heavily processed food is linked with weight gain is because it's really energy dense. So it's in a small package packed full of calories. So therefore we eat more calories in a short period of time. Now, I'm quite skeptical whether this is the main reason why.

why heavily processed food is bad for us, because I think there's other possibilities. And really interestingly, this study found that hard, minimally processed, so unprocessed food, and also hard, heavily processed food was consumed slower overall.

Okay. So the hard food, whether it was processed or unprocessed, was consumed slower overall compared to soft food. So hard, minimally processed foods in this case were classified as rice, which you might find hard to believe. Jonathan has classified as hard, but we'll get on to what soft is. You've got to be a nutritional scientist and think that rice is a hard food, but okay, keep going. Okay. Well, let me tell you what soft food is in a minute and then we'll see. Fresh, crunchy,

Veg was also classified as hard as well. Hard, heavily processed food included like fries, vegetable crisps or chips. What was interesting, more calories were consumed when people ate the soft food. And this was regardless of whether it was minimally processed or heavily processed soft food. And by soft food, we mean things like instant mashed potato, fish bites and fruit yoghurt.

got it. So it's like practically a liquid is the ultra process. That's interesting because I was just thinking about the difference between going and eating a meal from McDonald's and eating something that was more like a whole food in the way that our ancestors, you know, any meal would have been until 100 years ago, right? Where it would have been lots of plants and bees.

beans and lentils and, you know, sweet, any of these things, which are actually relatively crunchy, they're fibrous. It's going to take quite a long time to chew and bite. And so I thought you were going to push us towards this thing that these foods that we eat seem incredibly soft. And I think it's related to having sort of no fiber in them. And it sounds like actually in this study, you're not even that far. You're even just saying within ranges of things which are already quite processed that you're seeing this difference. Yeah.

Yeah. And I think what was interesting, there was like this graded response with unprocessed hard food being associated with the slowest rate of eating, processed hard food, the next slowest, unprocessed soft food getting faster, and then highly processed soft food, the fastest. Amazing. So it's not all to do with processing. It's also the texture of the food. Yeah.

So Sarah, you've sort of given us this whistle-stop tour of this new area of scientific research. What's your verdict? So my verdict is that this is a really exciting area of research that I'd love to explore further. And I think whilst there

there isn't interventional evidence to show definitively that people who eat fast, if they slow down the rate that they're eating, you know, improve their weight, improve other health measures. I think that the evidence is interesting enough to suggest that we should look into

it further. And I think it also really highlights an important area that we often talk about, Jonathan, about how we should think not just about the food that we're eating, but the way in which we're eating it, which we call our dietary habits. So we've talked before about the importance of thinking of the time of day that we're eating, about fasting. So our eating windows, for example, and I know that we often talk about intermittent fasting. So, you know, eating in a shorter period of time. And this is just one of those

other factors that I think is really interesting that we might want to consider when we think about our eating habits. I think it's really interesting that it seems to have come through so clearly in the data and in our own ZOE data as well as elsewhere. And I'm also struck that we can easily become quite divorced from

our own body signals about, are we hungry? Are we not hungry? There's a lot of really clever nutritional scientists who've been building food products that trick us past these points. They're things that are just so hyperpalatable, which again, it's in the same area of getting us to do things we don't want.

It wouldn't surprise me if we dig more into this that you see that speed of eating is also related to the sort of foods that you're eating because I think we all know that it's really easy to eat an ice cream really fast and to keep eating it because it's just so nice. I quite like nuts but

I'm never in a point where I've just got to finish the nutball. So there's definitely some linkages here, I guess, which is interesting. And so I think it'd be really interesting to do the studies. And I think what we tend to see right in this is there's very unlikely to be any magic bullet and there's a lot of interrelationship here. So I guess also, you know, the other thing I'm struck by is we haven't talked a lot about fiber, but it seems like, you know, if you're eating foods that are higher in fiber, we know they're incredibly good for your long-term health.

health, you know, can mean that you might live years longer. And I could see that the sort of foods that are higher in fiber are generally not hyperpalatable, like ultra processed foods. You probably have to chew them a bit more. So you can see how these things might work together or in the opposite direction, right? You're going to somewhere selling you fast food, you know, you don't need to chew any of this and

And therefore you can be sort of in the, it sort of feels like you're either in a good place or you could potentially be in a doubly bad place where the food isn't very good for you. And you're going to find it easy to sort of eat it very fast and overeat.

Yeah, and I think we know that fiber rich foods tend to be not very energy dense. So if you were to have two equal weight foods, but one had a lot of fiber in it, you'd have to actually consume probably three or four times as much of that food to get the same amount of energy as you would from energy.

a balanced weight meal that had little fiber in it. I think as well, Jonathan, do you know what's really fascinating thinking about eating rate, the speed in which we're eating, it's thinking about how we're eating now. And I'd be really interested to know whether people's eating rate has changed pre versus post COVID in terms of how many people now

are working at home are doing exactly what you said earlier that you do, which is you wolf down your food either between a Zoom meeting or on a Zoom meeting. Yet typically when we were in physically in an office environment, I think we would block time off because we knew that we had to either go and physically get food or, you know, we would be less or more self-conscious about eating it, I think, in front of people during a meeting. Yeah.

So I do wonder whether that's changed. That'd be really interesting to look at. Well, if you've enjoyed today's podcast and you'd like to try Zoe's personalized nutrition program to improve your health and manage your weight, you can get 10% off by going to joinzoe.com slash podcast. I'm Jonathan Wolfe. And I'm Sarah Berry. Join us next week for another Zoe podcast.