The surprising health impact of eating too fast

We’ve probably all been reprimanded for eating too fast at the dinner table or suffered the dreaded “itis” from eating way too much food at a family gathering.

Our society and the systems we’ve developed to feed it have ballooned so that they easily override our natural bodily systems that tell us when we’ve had enough to eat.

When nearly 50% of the United States population is projected to have obesity by 2030, can something as simple as changing the speed at which we eat really be an effective tool for losing weight and sustaining health?

In today’s short episode of ZOE Science & Nutrition, Jonathan and Sarah ask: What is eating rate, and does it have any impact on our health?

If you want to uncover the right foods for your body, head to, and get 10% off your personalized nutrition program.

Follow ZOE on Instagram.

Episode transcripts are available here.

Is there a nutrition topic you’d like us to cover? Email us at, and we’ll do our best to address it.


[00:00:00] Jonathan Wolf: Hello and welcome to ZOE Shorts, the bite-sized 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.

[00:00:17] Dr. Sarah Berry: Which is just a fancy way of saying how fast we eat our food.

[00:00:21] Jonathan Wolf: So does that have any impact on our health?

[00:00:23] Dr. Sarah Berry: Indeed, it does, Jonathan, and there's a lot more to eating rate than just how it interacts with our weight.

[00:00:29] Jonathan Wolf: Quick, let's get into it then, or should I say slow? Tell us a bit more about eating rates, Sarah.

[00:00:38] Dr. Sarah Berry: I dunno 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.

[00:00:51] Jonathan Wolf: Definitely. Uh, 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, you know, looking after the kids.

[00:01:03] Dr. Sarah Berry: That sounds familiar to me as well, and I think it's an unfortunate reality of just how busy many people's lives are now, and it's 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 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 where 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 behaviors according to what their parents reported.

[00:01:43] Jonathan Wolf: So in a nutshell. Sarah, you're saying eating faster makes it much easier for us to continue eating even when we're not hungry anymore.

[00:01:52] Dr. Sarah Berry: 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, uh, 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 1 study we saw that faster eaters ate on average 120 calories more per day than the slow eaters. Another trial suggests that reducing your eating speed by around 20% can lead to a reduction in energy intake of around 15%.

[00:02:29] Jonathan Wolf: 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, uh, if I eat more slowly, will I magically lose lots of weight?

[00:02:42] Dr. Sarah Berry: Okay. So, there hasn't been loads of research on this. Um, and I think this is what makes it exciting to be a nutrition researcher at a time when we are only just unraveling all of the evidence. But what has been shown is that, um, 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 hundred and five calories per day. The researchers also found that the fast eaters had a larger waist circumference by about three centimeters, which we know is important in terms of our, uh, metabolic health. And fast eats are also more likely to develop, um, overweight in 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 have been lots of other studies that have shown an association between how quickly you eat and excess body weight.

[00:03:54] Jonathan Wolf: Well, that is interesting, and I, and I, I would say surprising, I'm assuming 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?

[00:04:05] Dr. Sarah Berry: Yeah, so the first major area is your cardiometabolic health.

[00:04:09] Jonathan Wolf: So that's, you know, heart and blood vessels and also things like strokes and things like that, right, Sarah?

[00:04:15] Dr. Sarah Berry: Yeah, that's correct. And in 2017, a cardiologist from Hiroshima University in Japan studied more than a thousand, uh, people over five years to figure out the relationship between eating rate and something called metabolic syndrome.

[00:04:28] Jonathan Wolf: And I looked this up. And metabolic syndrome is the name that researchers now like to use for five risk factors, uh, for things like heart disease and diabetes and stroke, which are very serious. And those risk factors are, uh, apparently high blood pressure, high triglycerides, which I think we often call sort of, uh, blood fat, high blood sugar, low levels of good cholesterol, and finally a, uh, a large waistline compared to the average.

[00:04:58] Dr. Sarah Berry: That's correct. And what they found was that fast eaters were almost twice as likely to develop this metabolic syndrome. And a higher eating speed is 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 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.

[00:05:34] Jonathan Wolf: 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 and intake, body weight, and this sort of cardiometabolic risk, uh, in that study, which was UK and us.

[00:05:48] Dr. Sarah Berry: 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 a higher risk also of type two diabetes. And studies have shown that this may be because chewing more slowly stimulates more insulin release, which means better 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.

[00:06:14] Jonathan Wolf: And what about digestive issues, Sarah?

[00:06:16] Dr. Sarah Berry: We do know that fast eaters do often report poor digestion, and a study has shown that they may also get more acid reflux than slow eaters.

[00:06:25] Jonathan Wolf: So the overall message seems pretty clear. Sort of slow down, you know, at their kitchen table.

[00:06:30] Dr. Sarah Berry: 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.

[00:06:42] Jonathan Wolf: Now, Sarah, pretty much everything you've described so far are 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, you know, if one of those fast eaters switched to slow eating, it might not change anything. Right. And the gold standard. I, you know, I know in nutritional science, cuz you, uh, talk about this all the time, is a randomized controlled trial to prove that it's the eating speed that causes this, um, rather than everything else. And I know from many conversations with you and Tim and, 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 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, you know, 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 cuz you've already sort of removed all the people who were, who were sick. Where are we on this in terms of eating rate?

[00:07:47] Dr. Sarah Berry: 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, us 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 who 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 on 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 would be interesting to explore, and I 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 per meal. Now interestingly, they also felt more full when than the people who were eating faster, who ate more calories.

[00:09:02] Jonathan Wolf: That is 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 each bite?

[00:09:14] Dr. Sarah Berry: Um, so I think it depends on what's easy for you. There are other ways too. So firstly, uh, a study from China found that people cut their calorie intake by over 10% if they chewed their food 40 times instead of, uh, 15 times. This is because it had to 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 be too, to 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 dunno 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 cuz I'm putting my cutlery down, taking part in that conversation and slowing down naturally the rate I'm eating that way.

[00:10:08] Jonathan Wolf: So I have to say the idea of, on top of that, putting my cutlery down between each mouth or food seems a bit crazy. So I do prefer some of the other tips that we found in our research. So, uh, 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, and not thinking about it, drink water during the meal. So, that's sort of, uh, that's a way to interrupt, right? Uh, 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, um, shoving this in and the idea that you're, you know, you're doing good by waiting, you know, might be, 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?

[00:11:08] Dr. Sarah Berry: So I think that the texture of food's 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 rates 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 that it's energy dense, so it's uh, in a small package packed full of calories, so, therefore, we eat more calories in a short period. Now, I'm quite skeptical whether this is the main reason why heavily processed food is bad for us because I think there are other possibilities. And 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, is classified as, uh, as hard but gotta be nutritional.

[00:12:28] Jonathan Wolf: You've gotta be a nutritional scientist think that rice is a hard food, but okay, keep going.

[00:12:34] Dr. Sarah Berry: Okay. Uh, well, lemme tell you what soft food is in a minute, and then we'll see. Uh, 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, um, fish bites, and food yogurt.

[00:13:04] Jonathan Wolf: Got it. So it's like prac, practically a liquid, um, is the ultra process. That's interesting. Cuz I was just thinking about the difference between going and eating a meal from McDonald's and eating something that was more like, uh, whole food in the way that our ancestors, you know, any meal would've been until a hundred years ago, right? Where it would've been lots of plants and beans and lentils and you know, sweets, any of these things. So we're relatively crunchy, they're fibrous, and it's gonna take quite a long time to chew and bite. And so I thought you were gonna 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.

[00:13:51] Dr. Sarah Berry: 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.

[00:14:10] Jonathan Wolf: Amazing.

[00:14:11] Dr. Sarah Berry: It's not all to do with processing. It's also the texture of the food.

[00:14:19] Jonathan Wolf: So Sarah, you've sort of given us this whistle-stop tour of this new area of scientific research. What's your verdict?

[00:14:27] Dr. Sarah Berry: 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 is 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, uh, 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 how 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, and this is just one of those other factors that I think is interesting that we might wanna consider when we think about our eating habits.

[00:15:24] Jonathan Wolf: I think it's really interesting that it seems to have come through so clearly in the data and like in our own Zoe data as well as elsewhere, and, um, I'm also struck that we can easily become quite divorced from our sort of body signals about are we hungry, are we not hungry? Um, and that there's a lot of really clever nutritional scientists who be building food products that sort of trick us past these points, you know, that makes a thing, you know, they're the things that are just so hyper-palatable, which again, this is in the same area, right, of sort of getting us to do things we, we don't want. And it, it wouldn't surprise me if we dig more into this that you see that. You know, 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 ice cream fast and to keep eating it, right? Cause it's just so nice. And, um, I quite like nuts, but I, I'm never in a point where I've just got to finish the nut bowl. So there are some linkages here, I guess, which is interesting. And so I, I am. You know, 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, it'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. Uh, health, you know, can mean that you might live years longer. And I could see that, um, the sort of foods that are higher in fiber, Are generally not hyper-palatable, 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 somewhere selling you fast food, you know, you don't need to chew any of this. And, um, and therefore you can be sort of in the, it sort of feels like you're, 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 gonna find it easy to sort of eat it very fast and um, and overeat.

[00:17:25] Dr. Sarah Berry: Yeah, and I think we, we know that fiber-rich foods tend to be, um, not very energy dense. So, um, if you were to have two equal-weight foods, but one had a lot of fiber in it, you'd have to consume probably three or four times as much of that food to get the same amount of energy as you would from a balanced-weight meal that had little fiber in it. I think as well, Jonathan, do you know what's fascinating? Thinking about eating rate, uh, the speed in which we're eating. Is thinking about how we're eating now. And I'd be interested to know where the 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 are 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 cause we knew that we had to either go and physically get food or, or, you know, we would be less, uh, or more self-conscious about eating it, I think, in front of people joining a meeting. So I do wonder whether that's changed. That'd be interesting to look at.

[00:18:35] Jonathan Wolf: 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 I'm Jonathan Wolf.

[00:18:48] Dr. Sarah Berry: And I'm Sarah Berry.

[00:18:49] Jonathan Wolf: Join us next week for another ZOE podcast.

This podcast was produced by Fascinate Productions.