The real science of weight loss with the US’s leading nutritional scientist

Interactive Transcript

spk_0 This is the Guardian.

spk_0 When Robert F. Kennedy Jr. was appointed as Donald Trump's health secretary,

spk_0 he came with promises to tackle the broken food system.

spk_0 We shouldn't be giving 60% of the kids in school

spk_0 process food that is making them sick.

spk_0 We shouldn't be spending 10% of this in half program on sugar drinks.

spk_0 And for one researcher at the forefront of nutrition science,

spk_0 this seemed like good news.

spk_0 The rhetoric is spot on on those topics, and that's one of the reasons we were excited to

spk_0 have the potential opportunity to expand on our research and provide answers to the questions

spk_0 that Americans deserve.

spk_0 Kevin Hall is admired by scientists around the world.

spk_0 His groundbreaking research at the U.S. National Institutes of Health

spk_0 involves getting volunteers into the lab and studying in minute detail

spk_0 how the modern food environment affects their bodies.

spk_0 But when his findings didn't fit the administration's narrative,

spk_0 he says they were downplayed.

spk_0 The top researcher for the National Institutes of Health

spk_0 shocked the scientific and medical communities this week by announcing his early retirement

spk_0 and blaming it on censorship from RFK Jr.'s administration.

spk_0 The Department of Health and Human Services has rejected his claims of censorship.

spk_0 Now Kevin's on the outside continuing to follow the evidence.

spk_0 In his new book with journalist Julia Beliz called Food Intelligence,

spk_0 the science of how food, both nourishes and harms us,

spk_0 he interrogates everything from fat diets to glucose monitors and supplements.

spk_0 These kinds of hacks and trends of supplements and wearable devices and things like that

spk_0 have had limited capacity to change people's behavior over long periods of time.

spk_0 So today, what does Kevin Hall want us all to understand about diet, exercise, and weight?

spk_0 And what does he make of those now in charge of America's health?

spk_0 From the Guardian, I'm Ian Sample and this is Science Weekly.

spk_0 I wonder if you could take us back to some of the real basics, Kevin,

spk_0 in how we should think about the food we put into our bodies and the impact that has on our weight.

spk_0 And you talk in the book about this debate that scientists have been having about whether a calorie is

spk_0 a calorie essentially. Yeah, there's this idea that has a long history that what seemed to matter

spk_0 when it came to how much body fat we lose is the calories and the food that we eat.

spk_0 And it doesn't seem to matter whether or not those calories come from carbohydrates or fat,

spk_0 for example, as long as the number of calories was constant, the amount of body fat that you would

spk_0 lose would be similar. It turns out that we've done studies and others have done studies and it's

spk_0 very, very close to true. It's not quite true. There's very small deviations from that very basic

spk_0 rule of calorie swaps, but overall it's true. I think the misapplication of that knowledge has been

spk_0 the idea that, oh, well, then all we have to do is count calories in our diet and we will be able to

spk_0 predict how much weight should be gained or lost for every calorie change in our diets. And I think

spk_0 that what that misses the sort of calories in calories out idea when it comes to body weight regulation

spk_0 is it misses the physiological adaptations in both the number of calories the body burns through

spk_0 metabolism as well as how our appetite changes as we gain or lose weight. So you're saying that

spk_0 sort of our system doesn't stay steady while we're eating that metabolism changes the other

spk_0 things change that will affect how much weight we put on. Correct. Yes. So what happens in experiments

spk_0 when we bring people into the laboratory and cut calories in their diet is that, you know, within

spk_0 a few days we can see the number of calories that the body is burning go down and often goes down

spk_0 more than you'd expect just based on the fact that they're losing a little bit of weight and

spk_0 smaller people tend to burn fewer calories than larger people. More recently we've been able to

spk_0 detect that over more extended periods of time as people lose more and more weight their appetite

spk_0 increases above where they started at baseline so that if they were to relax their adherence to

spk_0 the diet they would tend to overeat calories and regain weight quite dramatically. And so it's the

spk_0 interaction between what I like to think of as two sort of parallel negative feedback circuits.

spk_0 One that decreases the number of calories the body is burning and one that is increasing our appetite

spk_0 that interact in this dynamic system to eventually determine how much weight we lose and where

spk_0 we'll end up plateauing at a lower weight. Can some of that be seen as the body really just wanted

spk_0 to keep things as they are that it wants to if it's on a diet it wants to go back to eating more

spk_0 food. That's correct. And in a given environment I think the fascinating thing is that the body is

spk_0 extremely resilient to shifts in body weight that what we find is that the body does react in a way

spk_0 to resist our efforts at weight loss and it requires a persistent lifestyle change and if people

spk_0 have the ability to do that in the face of a food environment for example that is acting against

spk_0 them then all the more power to them those are the rare examples.

spk_0 You were talking about how the body tends to resist weight loss but why does it not

spk_0 try and resist weight gain that has its own medical issues to come with it.

spk_0 Well in fact it does tend to resist weight gain. One of the things that we have learned also

spk_0 is that there have been experimental overfeeding studies in humans as well as in animal models

spk_0 and what you will see is that in those experimental models if you overfeed people more than they

spk_0 would like to eat their metabolism will speed up they will burn more calories than would be

spk_0 predicted based on the amount of weight that they'd gained and their hunger will drop quite

spk_0 dramatically so that when you remove the overfeeding period they will in fact eat very very few

spk_0 calories and lose weight and their metabolism will slow back down to a more normal rate.

spk_0 So we do have this system that seems to resist both weight gain and weight loss in a given environment

spk_0 and that's why we think that one of the most obvious explanations for why we might be seeing

spk_0 increased obesity prevalence is the slow steady shifts in the food environment that have given rise to

spk_0 what we see as an increased amount of this sort of defended body weight. A lot of people listening

spk_0 will be interested in what happens with exercise and weight loss and it's something we hear differing

spk_0 opinions on. I mean we know that exercise is great for our health but in weight loss terms a picture

spk_0 maybe isn't quite so clear what does the evidence say? Yeah the evidence for tying exercise to weight

spk_0 loss is quite interesting and a little bit disappointing especially for women it seems like when

spk_0 people do trials where they do supervised exercise so people are actually doing the exercise.

spk_0 For women it seems like they don't lose much weight at all on average again there's some people

spk_0 who lose weight and some others who actually end up gaining weight when they're doing this exercise

spk_0 program for men the situation is a little bit better but again the amounts of weight loss that we're

spk_0 seeing for quite robust amounts of exercise is often disappointing to people which is why I find it

spk_0 a little bit frustrating that people tie exercise to weight loss so prominently because I think people

spk_0 have this phenomenon of signing up for you know your New Year's resolution to join the gym and

spk_0 lose a little weight and they might be seeing all the benefits of exercise when it comes to metabolic

spk_0 health and functional capacity and the ability to live your life to a greater extent but because they

spk_0 don't see the scale budge very much they might end up giving up which I think is a big mistake

spk_0 especially given that it seems like where exercise has its sort of superstar qualities when it comes

spk_0 to weight loss is not in the weight loss itself but the ability to maintain the weight loss over

spk_0 long periods of time. So exercise may not help you shed the pounds but it may help you keep your

spk_0 weight healthy if you've already managed to lose weight is that right? Yeah that's right and I don't

spk_0 think there's any reason to not have exercise during the weight loss period just don't tie the

spk_0 amount of exercise that you're doing to the weight loss and don't be discouraged by the fact that

spk_0 it might not be seeming to correlate with how much weight you're losing from one week to the next.

spk_0 A lot of the messaging that we are exposed to from the diet industry I suppose we could call it

spk_0 pushes this idea that weight is something we have total sort of individual control over that it's

spk_0 all about motivation and willpower but in your book it's clear that it's more complex than that

spk_0 there's there's a whole load of other factors coming into play. Right I mean one of the first is

spk_0 genetics body size is highly heritable within a given environment somewhere between 40 and 70%

spk_0 of the variability and body size between people is due to our genes. Now it's not you know a handful

spk_0 of genes what we've now understand with obesity is that there's more than a thousand genes all

spk_0 playing very very tiny parts in determining in a given environment where we're sort of regulating

spk_0 our body weight. Most of those genes are genes that are acting in our brains and so we believe that

spk_0 many of those genes are acting in the control of food intake and the science seems to suggest

spk_0 that that's correct but I guess the question then is what can we do to kind of change our body size

spk_0 in an environment that is promoting obesity and so I think we have two options one we can start to

spk_0 interfere with the biology which we have had some success with in recent years with interventions

spk_0 like bariatric surgery as well as these new weight loss medications that target the GLP1 receptor

spk_0 and other receptors in the brain as well as being able to shift that food environment to one that

spk_0 is promoting not the ultra-processed foods so that they don't cause the ones who were most susceptible

spk_0 to the shifts in the food environment to beginning that weight in the first place.

spk_0 You mentioned ultra-processed foods Kevin and it's probably the area that you're best known for

spk_0 and you say in the book that this is a quote that they seem to reset whatever it is that

spk_0 used to help us regulate our body weight at lower levels but the actual mechanism of how they're

spk_0 doing that still seems to be elusive what is the research showing so far?

spk_0 Yeah so so far what we're trying to understand is two questions one what is it about those foods

spk_0 themselves that might cause excess calorie consumption and one of the things that we have focused in on

spk_0 is the fact that in the formulation of those foods on purpose one of the things that food scientists do

spk_0 is they try to eliminate as much of the water content of the foods as possible so that they'll

spk_0 have longer shelf life because water content in foods promotes bacterial growth and as a result of

spk_0 doing that what they end up doing is concentrating the calories and what we're finding is that that

spk_0 so-called energy density of the food is one of the main drivers by which ultra-processed foods

spk_0 seem to be causing people to overeat calories another aspect that we're really interested in is whether

spk_0 or not combinations of nutrients like combinations of high fat and high sugar or high fat and high salt

spk_0 or high carbs and high salt the so-called hyper-palatable combinations of foods that are not typically

spk_0 found in nature those formulations in ultra-process foods are potentially also driving excess calorie

spk_0 intake and we seem to find some evidence in our controlled feeding studies that both of those

spk_0 factors might be playing major roles and fairly recent work you've done showed that this is a pretty

spk_0 nuanced picture around some of these foods so I wonder if you could tell me about the study

spk_0 you did where you put people on these four different diets yeah so that that's an unpublished

spk_0 study that's some interim results that we presented last year and what we were able to show is that

spk_0 a very highly ultra-processed food environment as long as it didn't contain many of these

spk_0 hyper-palatable foods or didn't have very high calorie density didn't promote excess calorie

spk_0 consumption and in fact promoted very similar calorie consumption to a minimally processed diet that

spk_0 had no ultra-processed foods and so we sort of take that as you know encouraging news that we're

spk_0 beginning to target some of the mechanisms by which food environments that are rich in ultra-process

spk_0 foods typically cause excess calorie intake and if we can understand those mechanisms then we can

spk_0 start to give our policy-making friends the ammunition that they need to isolate you know what is

spk_0 it about these foods that we need to start to regulate or invent policies around.

spk_0 Ironically it was Kevin's work exploring these nuances around ultra-processed foods which brought

spk_0 on end to his career at the NIH where he'd worked for 21 years. A common narrative says that ultra-process

spk_0 foods are addictive and the same way drugs can be so Kevin wanted to understand whether this was

spk_0 true he believes that hyper-palatable UPFs can be addictive but is the mechanism the same.

spk_0 Would an ultra-processed milkshake cause the same large surge of dopamine in the brain that can

spk_0 happen with highly addictive drugs. Surprisingly what we found was we were unable to detect the

spk_0 significant dopamine increase in the brain after consuming the ultra-processed milkshakes high

spk_0 and fat and sugar. It doesn't mean that there wasn't any dopamine increase it's just not

spk_0 happening to the same extent as these highly addictive drugs. We wrote up a paper and it was

spk_0 coming out in a journal and it basically said yeah look these foods might be addictive in some

spk_0 people but they seem to be working slightly differently than these highly addictive drugs

spk_0 and we had a press release ready and we're ready to kind of tell the world about this discovery

spk_0 and we were told we weren't allowed to issue a press release in fact we weren't allowed to talk to

spk_0 reporters about this we were only allowed to submit answers to written questions from the reporters

spk_0 and in fact one of the reporters at the New York Times who wanted to interview us got a phone call

spk_0 from the communications department at Health and Human Services and said I was wondering whether

spk_0 or not she was really writing a piece about Robert F. Kennedy Jr. because the results of this study

spk_0 didn't match what he thought was happening with ultra-processed foods. So it was very sort of chilling

spk_0 that our science was being highlighted in this way and being deemed as not consistent with the

spk_0 beliefs of the current Health and Human Services secretary and when I ended up writing written

spk_0 responses to the journalist questions my responses were edited and downplayed the importance of

spk_0 the study saying it was very small and more or less should be ignored when in fact it was the

spk_0 largest study of its kind conducted and so that was the the genesis of me realizing that despite

spk_0 this research that we had hoped would be expanded upon that that was going to be held to a very

spk_0 high degree of public scrutiny by the political appointees at HHS when I tried to get some clarity

spk_0 on that I got no response for weeks so I made the decision that without that sort of assurance that

spk_0 you know I wasn't going to continue to experience meddling in the reporting of our science

spk_0 and in fact you know the reporting of future studies and maybe even the design of future studies

spk_0 I didn't want them meddling in those things I decided to take the early retirement option that

spk_0 was offered so do you think that they either wanted or would have been happier to see evidence of addiction

spk_0 oh yeah I think that's the problem is that they are very interested in science that seems to

spk_0 support their narrative and they're very interested in downplaying science that seems to not support

spk_0 their narrative and much the same way a trial lawyer might which is what Robert F. Kennedy Jr.'s

spk_0 background is and so my view is that oftentimes science doesn't fully support a narrative it often

spk_0 introduces more questions and complicates the narrative and my worry is that this administration

spk_0 is not interested in the science they think that they have the answer they think they have a compelling

spk_0 narrative and any science that seems to complicate that should be downplayed and ignored

spk_0 this can't be an easy decision to make to leave after that amount of time you know the lab you've got

spk_0 you know everything is is set up for you to do the work that you want to do you can get the

spk_0 grants and so on like that which all suggests that this is this is a major problem that this

spk_0 wasn't sort of a trivial thought in your side why is it so important yeah I mean I think that

spk_0 we have to stand up for our scientific integrity I think we've seen that this is not just isolated

spk_0 to me obviously I may have been one of the first ones to be vocal about it at the NIH but what we've

spk_0 seen is folks who maybe not have been in as high profile areas of science many of them have taken

spk_0 these options to leave the National Institutes of Health others didn't have those options available

spk_0 to them but it was very disappointing to leave I had joked with my wife about retirement many times

spk_0 that I did plan to never retire I love my job so much we had the ability to do what I thought was

spk_0 important science and make these kinds of advances and and ways that would be difficult to do elsewhere

spk_0 so it was a very very difficult decision I hope to one day to be able to return to government

spk_0 service and to be able to do this kind of research again if not at the NIH maybe back in my home

spk_0 country of Canada who knows we'll see what happens

spk_0 Kevin it can be difficult from the outside to really get a handle on what's happening

spk_0 in the US and you know for example on paper Robert F. Kennedy Jr looks like a promising health

spk_0 secretary to tackle some of the problems that you've outlined in the book I mean he has raised

spk_0 issues with the food industry I wonder whether you have any faith in the administration to

spk_0 to regulate where it's needed and to tackle the specific kinds of of problems that you're talking

spk_0 about yeah I mean that's one of the things that was really interesting and surprising to me was

spk_0 because the rhetoric is right when it comes to diet related chronic disease right but unfortunately

spk_0 I think what we've seen is that the actions are not matching the rhetoric practical programs for

spk_0 example the United States Department of Agriculture had programs that were supporting local farmers

spk_0 delivering fresh fruits and vegetables to school programs and other institutional settings

spk_0 and those programs were cut education programs on how to actually prepare healthful foods in

spk_0 convenient ways those programs were cut even the policy changes that have been put forward are

spk_0 you know really minor effects on our food system things like suggesting that Coca-Cola

spk_0 create a new line of products that have cane sugar instead of high fructose corn syrup in them

spk_0 not removing high fructose corn syrup from their products not that there's anything different

spk_0 from a scientific perspective between high fructose corn syrup and cane sugar

spk_0 these sorts of the count as maha wins are not likely to move the needle on public health when

spk_0 it comes to diet related chronic diseases and as a result they're going to explain this enormous

spk_0 amount of political capital which was earned by the grassroots folks in the make America healthy

spk_0 again movement to do things that are going to have a meaningless effect on public health

spk_0 Kevin thank you so much thanks for having me

spk_0 thanks again to Kevin Hall Kevin's book co-authored with journalist Julia Ballouze is called

spk_0 Food Intelligence the science of how food both nourishes and harms us to support the Guardian you

spk_0 can order your coffee via guardian bookshop.com and that's all from us today this episode was

spk_0 sound designed by Joel Cox an executive producer was Ellie Bury we'll be back on Thursday see you then

spk_0 this is the Guardian

spk_0 before you

The real science of weight loss with the US’s leading nutritional scientist

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