FLORA LICHTMAN: Hey, it’s Flora Lichtman, and you’re listening to Science Friday.

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Today on the show, how a mega-popular reality show upended what scientists thought they knew about metabolism.

KEVIN HALL: I was interested in participating as a researcher, observing these folks who were doing this sort of natural experiment at 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.

FLORA LICHTMAN: 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.

BOB HARPER: Do not be sloppy. Finish this strong, Joelle. No, Joelle, don’t do it. Don’t do it. Dig, Joelle! Dig!

FLORA LICHTMAN: The show had issues, and it hasn’t aged well. And while the weight loss landscape has gotten more complex with GLP-1 drugs, like Ozempic and Wegovy, 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 has 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 Belluz, science journalist based in Paris. Welcome to both of you to Science Friday.

JULIA BELLUZ: It’s a pleasure to be here.

KEVIN HALL: Thanks for having us.

FLORA LICHTMAN: OK, let’s start with this. What is Food Intelligence?

KEVIN HALL: 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.

FLORA LICHTMAN: Is the idea that we are all born with a sort of innate understanding of what our body needs?

JULIA BELLUZ: As a layperson, 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.

FLORA LICHTMAN: Modern food environments, such as ultra-processed foods, fast food.

JULIA BELLUZ: Exactly, yeah. The kind of foods that many Americans in particular are surrounded by now.

FLORA LICHTMAN: Julia, what drew you to writing about nutrition and food?

JULIA BELLUZ: 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 Canadian. And when I moved to the US, 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 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 various supposed panaceas for people’s weight and diet struggles.

And then when I would talk to Kevin, 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 individual hacks and fixes that scientists like Kevin appreciated for most people in the current food environment just didn’t work.

FLORA LICHTMAN: Kevin, I want to talk about some of your research. You worked at NIH a long time, but there’s this interesting eddy on your resume, where you worked as a scientist on set on the TV show The Biggest Loser. What were you doing?

KEVIN HALL: Yeah, so that’s while I was still at NIH. And I was really interested in understanding what was happening to these folks. This was a very strange lifestyle intervention that was televised on national TV for many, many seasons. And these folks were subject to a whole lot of abuse. But in the space of that abuse, they were doing a ton of 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 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 at 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.

FLORA LICHTMAN: What did you learn?

KEVIN HALL: 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 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 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. Most folks had regained most of the weight, or at least 2/3 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 that 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.

FLORA LICHTMAN: What does that tell us about our understanding of metabolism?

KEVIN HALL: 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.

FLORA LICHTMAN: So it’s not the metabolism that’s driving the weight loss is what you’re saying.

KEVIN HALL: Right. The way that we say it in the book is it’s not metabolism, stupid.

FLORA LICHTMAN: [LAUGHS] 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.

JULIA BELLUZ: So part of this quest that I had to understand 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 I was someone who had 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 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 genes for most conditions, they’re also not determinative, unless you have a rare single-gene disorder or something.

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FLORA LICHTMAN: We have to take a break. But don’t go away, because when we come back, how much protein should we really be eating?

KEVIN HALL: For most folks, they already get pretty close to double the recommended daily allowance.

FLORA LICHTMAN: Vermont listeners, we’ll be in Burlington on Friday, October 17 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 sciencefriday.com/vermontlive.

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FLORA LICHTMAN: 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.

MARY KAY: 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.

KEVIN HALL: So that’s a really interesting question because I think that the amount 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 the 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.

FLORA LICHTMAN: Pick up some weights. Is that what I’m hearing?

KEVIN HALL: 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.

FLORA LICHTMAN: I don’t need to have a protein cold foam from Starbucks–

KEVIN HALL: Not likely.

FLORA LICHTMAN: –to be healthy.

KEVIN HALL: Not likely. It’s probably defeating the purpose with all the sugar and whatnot that’s probably being added to it.

FLORA LICHTMAN: We got another related question from Nicole in California.

NICOLE: 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?

KEVIN HALL: Yeah, so 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 building blocks, those amino acid building blocks, are being used to 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, 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 if you’re overeating calories. And those extra calories end up as body fat.

FLORA LICHTMAN: 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?

KEVIN HALL: 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 it’s the dietary fat that makes you fat or the dietary carbs that are making you fat seems to flip-flop, 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, and 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 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.

FLORA LICHTMAN: OK, last question. 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-processed foods on our diet?

JULIA BELLUZ: 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.

KEVIN HALL: 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.

FLORA LICHTMAN: Julia Belluz, 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.

JULIA BELLUZ: Thank you so much.

KEVIN HALL: Thank you.

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Today’s episode was produced by Kathleen Davis. I’m Flora Lichtman. Thanks for listening.

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