Science Friday - It’s Not Just You—Bad Food Habits Are Hard To Shake

Episode Date: October 14, 2025

Remember “The Biggest Loser”—the show where people tried to lose as much weight as quickly as possible for a big cash prize? The premise of the show was that weight loss was about willpower: With enough discipline, anyone can have the body they want.The show’s approach was problematic, but how does its attitude toward weight loss match our current understanding of health and metabolism? The authors of the book Food Intelligence, nutrition scientist Kevin Hall, who studied “Biggest Loser” contestants at the NIH; and science writer Julia Belluz, join Host Flora Lichtman and answer listener questions about nutrition, diet fads, and metabolism.Read an excerpt of Food Intelligence: The Science of How Food Both Nourishes and Harms Us.Guests:Julia Belluz is a science journalist based in Paris.Dr. Kevin Hall is a nutrition scientist and former NIH researcher based in Kensington, Maryland.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flora Lickman, and you're listening to Science Friday. Today in the show, how a mega-popular reality show offended what scientists thought they knew about metabolism. I was interested in participating as a researcher, observing these folks who were doing this sort of natural experiment. A study that couldn't have been done otherwise had they not already been signing themselves up for this kind of abuse on a national television show. Remember the biggest loser? That show where people tried to lose as much weight as quickly as possible for a big cash prize. The premise of that show was that weight loss was about willpower. With enough discipline, anyone can have the body they want.

Do not be sloppy. Finish this strong, Joelle. No, Joelle, don't do it. Don't do it. Don't do it. Dig, Joelle, dig! The show had issues, and it hasn't aged well. And while the weight loss landscape has gotten more complex with GLP1 drugs like OZemphic and Wagovi, a social media-fueled wellness industry, infinite fad diets, the underlying idea that weight loss and health is as simple as Move More, eat less, hasn't gone away. But does that match current research? How is our understanding evolved? A new book written by a journalist and a nutrition scientist who, among other things, studied biggest loser contestants.

breaks down the science of nutrition and metabolism and what we've learned in the two decades since that show premiered. The book is called Food Intelligence, and I want to bring on the authors. Dr. Kevin Hall, nutrition scientist and former NIH researcher based in Kensington, Maryland, and Julia Ballou's science journalist based in Paris. Welcome to both of you to Science Friday. It's a pleasure to be here. Thanks for having us. Okay, let's start with this.

What is Food Intelligence? Well, the title is really a play on the idea that people really have a pun intended hunger for knowledge about what it is that they're eating and how it works inside their bodies and what it means for health. And so the idea of the book is to provide people with the necessary background about the science of nutrition and metabolism and give them some intelligence about the foods that they eat. Is the idea that we are all born with a sort of innate understanding of what our body needs? This was, as a lay person, this was one of the most surprising things in reporting this book, that we are all as living things equipped with this symphony of internal signals that guides our eating behavior to a much greater extent than many of us realize. And what we found in the book is that modern food environments have interrupted that system that has served humanity quite well over many, many thousands of years.

Modern food environments such as ultra-processed foods, fast food. Exactly, yeah, the kind of foods that many Americans in particular are surrounded by now. Julia, what drew you to writing about nutrition and food? So I'm someone who struggled with my weight. I was a chubby kid and teenager, and my weight fluctuated up and down, including having obesity. So I'm someone who struggled with my weight, and I'm, I'm Canadian, and when I moved to the U.S., there was this time when obesity rates were soaring as they are now.

And I became curious, why is it that so many people are like me? They seem to know what they should be eating. They want to be eating better, but they can't or they struggle to. And in that reporting, I got to know Kevin, who was doing this fascinating research on kind of many different areas of nutrition science. And when I would talk to him, so much of what he was saying was so disconnected from where the public conversation was at. As it is now, there was a lot of conversation about fad diets or supplements or, you know, various supposed panaceas for people's weight and diet struggles. And then when I would talk to Kevin, that the solutions were really different. It seemed like bariatric surgery was the only effective tool we had for dramatic.

and long-term weight loss at the time. The GLP-1 drugs were already coming onto the scene. They were being used for diabetes, and people were seeing weight loss in those trials. But the public conversation still fixated on these kind of individual hacks and fixes that scientists like Kevin appreciated for most people in the current food environment just didn't work. Kevin, I want to talk about some of your research.

I mean, you worked at NIH a long time, but there's this interesting Eddie on your resume where you worked as a scientist on set on the TV show The Biggest Loser. What were you doing? Yeah, so that's while I was still at NIH, and I was really interested in understanding what was happening to these folks.

You know, this was a very strange lifestyle intervention that was televised on national TV for many, many seasons. And these folks were, you know, subject to a whole lot of abuse, but in the space of that abuse, they were doing a ton of exercise, different kinds of exercise. And it wasn't clear how that crazy lifestyle intervention was influencing their bodies in terms of how much of the weight that they were losing was coming from body fat versus muscle, for example, or whether or not their metabolisms would slow down as typically happens with diet programs that don't involve a lot of exercise. There was a lot of discussion back then that exercise would boost

metabolism and therefore you wouldn't experience the usual metabolic slowing. So I was interested in participating as a researcher observing these folks who were doing this sort of natural experiment, a study that couldn't have been done otherwise had they not already been signing themselves up for this kind of abuse on a national television show. What did you learn? Yeah, we learned that many of the things that we had presumed about exercise and about metabolic slowing didn't turn out to be true. So despite the fact that these folks were engaging in roughly three hours of vigorous exercise every day of the week, their metabolic rate did slow down by many hundreds of calories per day on average. But, you know, maybe most surprisingly, it was the folks who had the greatest slowing

of metabolism who lost the most weight. And this was a trend that we saw. kind of six years later, when we brought these folks back to the NIH Clinical Center to study them, six years after the lights of the television cameras turned off, you know, most folks had regained most of the weight, or at least two-thirds of the weight that they'd lost on the program. Some people regained all of it and more. One person continued to lose weight, and one of the things we were interested in was whether or not the metabolic slowing at the end of this crazy competition predicted

who would regain the most weight, as had been assumed to be the case in previous hypotheses. And again, we had a surprise that there was actually no relationship between the folks who had the greatest slowing of metabolism after weight loss and the subsequent weight regain. And in fact, once again, six years later, the ones who were most successful at keeping the weight off, they boasted the slowest metabolisms. What does that tell us about our understanding of metabolism? Well, it tells us that metabolism isn't driving the cart here, right? It's actually something else that it's following. It's more the cart than the horse. And I think that that's a new way that we

are beginning to think about this. It's not determinative of body weight change in the way a lot of people like to think when they say, oh, I just have a slow metabolism and that's the reason that I might be heavier than I would like to be. It's more complicated than that. And in fact, the metabolism seems to be responding to the lifestyle interventions that these folks had experienced and it responds in proportion so that if you do more changes in your diet and exercise, metabolism will respond, but you'll also receive the greatest amount of weight loss or maintenance of weight loss. So it's not the metabolism that's driving the weight loss, is what you're saying. Right. The way that we say it in the book is it's not metabolism, stupid.

Perfect. That's right at my level. Thank you, Kevin. Julia, in your quest to better understand metabolism, you hermetically sealed yourself into a metabolic chamber. Please tell us about this experience. So part of this quest that I had to understand, you know, why was I a person who struggles? Why do so many of us struggle with our body weight? The first place I actually turned was having my metabolic rate measured in this metabolism chamber at NIH. And I was quite sure that this must be one of the reasons. Yeah, I was someone, who had, you know, found it difficult to keep my weight down and had to put a lot of conscious effort into it. And as it turns out, my metabolism, my metabolic rate was completely normal

for someone my age, gender, and body size. So this did not explain anything. And that obviously led to more questions than what was it. And in the process of reporting on the book, I had my genes analyzed as well, and I found out I am at a much higher risk for both obesity and diabetes than most of the population. But all the researchers I spoke to, including Kevin, said, you know, genes for most conditions, they're also not determinative unless you have, you know, like a rare single gene disorder or something. We have to take a break, but don't go away because when we come back, how much protein should we really be eating? For most folks, they already get pretty close to double the recommended daily allowance.

Vermont listeners will be in Burlington on Friday, October 17th for a live Science Friday stage show. We're digging into the future of food, and we'd love to have you at the table. Join us. Tickets are at science friday.com slash Vermont Live. We also had tons of questions from listeners who had just many queries about nutrition and diet. So let's go to the first one. This is Mary Kay. I'm calling from Florida. I'm 73.

And there's a lot of information about how much protein I really should be eating to not be losing muscle mass and all those good things. I would love to know what the really latest information is on how much protein we need at different ages. Thanks so much. Love your show. So that's a really interesting question because I think that the amazing. of protein that people should be eating very much depends on the stage of life that they're in, and whether or not you should be worrying about it also depends on the stage of life. So, for example, in folks who are older, who are likely to be in settings that have reduced

protein availability and are at risk for losing a lot of muscle mass, then people seem to think that increasing the amount of protein from their recommended daily allowance is a good idea. We talked to a protein researcher in reporting for the book, Stuart Phillips, who makes a very poignant case that folks who are elderly and in institutional settings in particular are particularly at risk for losing muscle mass and losing mobility, and he recommends that people eat double the recommended daily allowance. For most folks, they already get pretty close to double the recommended daily allowance, and they shouldn't be worried too much about the protein.

content. If you're worried about muscle mass, and this is true across the board, the best thing that you can be doing is resistance exercise. Pick up some weights. Is that what I'm hearing? That's exactly right. Pick up some weights. Get active. Do some of that work because that's going to have much more bang for your buck than any increases in these protein supplements in particular that people are using. Like I don't need to have a protein cold phone from Starbucks. Not likely. Not likely. It's probably defeating the purpose with all the sugar and whatnot that's probably being added to it. We got another related question from Nicole in California. My question is, I've heard, that if you just eat a lot of protein and you don't use it

through exercising or moving your body, that it just turns into fat. Does protein turn into fat if it's not used? Yeah. So, I mean, I think that this is part of the idea that, well, number one, the protein that you eat, is being broken down in your gut and is being used, those kind of building blocks, those amino acid building blocks are being used to kind of create other proteins inside your body. It's not just about muscle and it's not just about powering muscle. Certainly, that was the debunked idea from the 19th century. The idea here is that you can overeat protein and that protein that's not

being used will be essentially those fuels will be used to fuel metabolism and if you're eating excess calories certainly you will then gain body fat and we outline the pathways that that happens in the book and some of the really interesting shifts in the fuels that the body is using when you're eating protein and fat and carbohydrates in the diet and how that all works out in the end to if you're overeating calories, and those extra calories end up as body fat. You know, we got a lot of questions about fad diets, and it feels like every diet has some special formula of fat, carbs, protein that we should be shooting for. Are there actual guidelines backed by science that work for most people about the correct ratio of those food groups? Yeah, no, one of the things that people get confused about

is that typically there's this ongoing back and forth debate about the evil nutrient, right? Protein seems to have been mostly spared in that discussion, but whether or not it's the dietary fat that makes you fat, where the dietary carbs that are making you fat seems to have flip-flopped depending on whether or not low-carb or low-fat diets are the most popular fad diet of the era. And one of the things that we've done in our research is to try to better understand how does the body use carbohydrates and fats? And in particular, how does the body shift its fuel usage when you make very large swings

in the ratio of carbs and fat in the body? And our research, as well, as many other people's research over the years, have really shown that carbs and fat, despite being pitted against each other in these diet wars, are really like good colleagues. They kind of stand in for each other when the other one's out. And the idea here is that we're omnivorous species. We can thrive on a wide variety of different diets. And the body has been evolved in such a way as to choose the fuels that it's using based on the ratio of carbohydrate and fat in the diet.

And either one can do its job. And if you're consuming excess calories, either in terms of higher amounts of carbohydrates or higher amounts of fat, almost identical amounts of body fat will be changed. So that goes for also the deficits as well. If you're eating too few calories to maintain your weight, it doesn't matter much whether or not that's a low-carb diet or a low-fat diet. Okay. Last question.

You know, whether dopamine is the culprit in ultra-processed foods or not, you both point to our food environment, ultra-processed foods, as problematic. what would it take to actually loosen the grip of ultra-process foods on our diet? We describe in the book how we're basically in this total inversion of the food environment that we should have. So the worst for you foods are the most accessible, available, affordable, easy to put in your mouth, basically, and the best for you foods are the hardest to come by and they tend to cost more. And so, yeah, we call for basically an inversion of this food environment.

and also meeting people where they are. So that means giving them these prepared, healthy, sometimes even processed options that they can eat easily if they don't have the time, wherewithal, or desire to cook. What we think we need to do is make changes in policy and regulations to, first of all, target the ultra-processed foods that are potentially the worst players.

That should be based on science and the mechanisms by which we think that those ultra-processed foods are playing a role in driving diet-related chronic disease. And then there's a whole suite of policy changes that one could make in order to reduce the prevalence of those foods. But in addition, and most importantly, perhaps, make the healthy alternatives, some of which might actually be ultra-processed healthy foods. That's not really an oxymoron, really, believe me.

And if we could make those healthy alternatives equally convenient and compelling and readily available to folks, that's the path forward. Julia Ballou's science journalist based in Paris and Dr. Kevin Hall, nutrition scientist and former NIH researcher based in Kensington, Maryland. They are the authors of food intelligence, the science of how food both nourishes us and harms us. Julia, Kevin, thanks for joining us today. Thank you so much. Thank you. Today's episode was produced by Kathleen Davis. I'm Flora Lichtman. Thanks for listening.