'Welcome to Chasing Life. You know, something I've been thinking a lot about is how despite all of our scientific breakthroughs, despite these mind-blowing medical advancements we make every year, and some of them are truly, truly remarkable, we still often struggle with the basics. We can cure previously incurable diseases, but keeping ourselves healthy, we've actually not done such a great job with. There are a lot of examples I can point to, but the most glaring, and I think probably the most fundamental. Is how we eat, how we nourish ourselves. According to the Centers for Disease Control and Prevention, only about one in 10 adults, 10% in the United States, actually eats the recommended amounts of fruits and vegetables. Three quarters of US adults are either obese or overweight. We spend $4 trillion on health care, and we are some of the least healthy people in the developed world. And I really do think a lot of it has to do with our eating habits. We just don't eat well. And the consequences of that are far-reaching, because along with those rising obesity rates come a suite of other health issues, type 2 diabetes, cardiovascular disease, fatty liver disease, cancer. And then there are all the cultural consequences as well. Just look around you. Think about all the ads, all the people who claim to have the secret ingredient to a slimmer and supposedly happier life. You know what I'm talking about. The YouTubers warning of symptoms of food addiction, who then prescribe, out of the box, hacks to cutting calories.

That's why I do the sardine challenge, to decouple food from pleasure.

Or maybe all the people on TV over the years spreading the gospel of a certain diet or another diet, even the sexy diet.

Diet shrink your fat cells speed up your metabolism and activate your skinny jeans

And then, of course, the podcasters who often tell people the reason they are failing to lose weight is because, quote unquote, they have killed their metabolism.

In fact, if you 've got a slow metabolism, good luck trying to burn body fat. Let's talk about this.

'Claims like that last one about a slow metabolism really frustrate my guest today to no end. My guest is Dr. Kevin Hall. He's a former researcher at the National Institutes of Health and one of the world's leading experts on food science. He has co-authored a new book called Food Intelligence: The Science of how Food Both Nourishes and Harms Us. In it, he dispels many popular myths we have about weight loss. And he breaks down the real drivers of the obesity crisis based on decades of research. Kevin knows what he's talking about and he's here today to help us separate fact from fiction and also to explain what metabolism really is and what it isn't. And show why so much of what we've been taught about food, calories, and willpower is far more nuanced than we've been previously led to believe. I'm Dr. Sanjay Gupta, CNN's chief medical correspondent. And this is Chasing Life. You know, one of the reasons I really wanted to talk to you is because there is so much information out there about food. And you and I, I think, are both health conscious people, try to practice what we preach, and yet it can be confusing. So I wanted to come to the guy who's actually done a lot of the hard work in this area. It's just so striking to me how much advice, quote unquote, there is out there. And I'm just curious, just broadly speaking, You've been at this for a long time. How do you see the rise of the wellness influencer talking about what you should eat, when you should, all that sort of stuff? How has that changed and how has that affected your work?

Right. It's been really fascinating to see this, what used to be, there's a very long history of people thinking they'd figured out, you know, the truth about food and nutrition and how best to eat. And this has kind of been happening for centuries in nutrition science, but you know the magnitude of the information that we now have and people with very large platforms having extremely strong opinions thinking they've got it all figured out and might make very bold claims like you've been lied to in the past by scientists and the government and whoever else is underlying the nefarious food industry and basically basing sometimes very sensible advice, sometimes not so sensible advice and often a kernel of truth which has been well founded scientifically and then they run with that and oftentimes think that they've got the entire explanation and I think the frustrating thing from a scientist perspective is that often times. That is treated as fact, and very few people go about testing those ideas, right? Actually saying, okay, this is a really intriguing model of how we think the human body works in relation to specific kinds of diets and foods. Let's go out and figure out if it's true, because it doesn't matter how compelling your story is and how much you've convinced yourself and your followers that this is the truth. Science doesn't work that way right? That's just the first step of the scientific process is that you think you got something figured out and now we have to go and test it.

Yeah, no doubt. And just to be totally candid about it, the people who are trying to influence you online, they stand to make money often either through their social media platforms or through selling products and things like that. So there's other things at play here that didn't used to be a play before. You could give advice, but you weren't necessarily monetizing that advice and now people are. So the more audacious or outlandish the claim, the better in terms of what they're trying to achieve. Let me, let me ask you some, just some basic questions. Metabolism is at the heart of, I think, this entire discussion, how we metabolize food. What is metabolism?

Yeah, metabolism is one of the things that most people don't really know about. They kind of think it has something to do with how much food we can eat without gaining weight or something like that. Metabolism is just this incredible biochemical process that basically turns the food that we eat and the oxygen that we breathe into essentially, as my friend Charles Brenner says, into everything we are and everything we do. It's harnessing the continuous flow of matter and energy in our food and in our breath and powering every cell in our body, as well as the bodies and cells of practically every organism that we have ever encountered. It's a fundamental component of life and it's just incredibly fascinating and I just find it incredibly frustrating sometimes that this idea of metabolism, this really beautiful physiological process is kind of talked about as, oh, well, if you take the supplement, you can boost your metabolism and lose weight or. Metabolism is the thing that keeps you from losing weight, and so much misinformation about metabolism, and it's something that has really distracted people, I think.

Is there a fundamental misconception, do you think, just in your years of research, is there a fundamental misconceptions people have about metabolism?

'Yeah, I think that the fundamental misconception that I've seen over and over again, and again, it gets to some of the science and how it's evolved, was the idea that people with obesity have a slow metabolism. Right. And there are some people, that's true of a minority of people with obese, but generally larger people have faster metabolisms than smaller people. And it's only when we started to really quantify the overall metabolic rate of human. In a careful way and of a wide variety of people that we realize that because the way that that sort of myth entered into the lexicon, which has kind of continued to this day, came from basically asking people what they ate and trying to kind of work out, well, if they ate this much, then we can figure out how many calories are in the foods. Then if you just look at how much people with obesity say that they eat versus how someone who's lean, says that they eat, it turns out that the number of calories seems to be relatively less in the people with obesity. And I think what we now understand is that they're all under-reporting the amount of calories that they are eating. It's one of those things that's very difficult for people and nutritionists and scientists even to quantify how many calories people are eating just by monitoring their diets or asking them to keep diet records or asking to say how much of certain kinds of foods they eat in the past. But that error in our measurements for many, many years before we were making direct measurements of metabolism led people to a conclusion that, well, if they're eating less calories and they're maintaining their weight, then they must be burning less calories. And then came a bunch of studies that said, well, actually, when we actually directly measure people's metabolisms, people with obesity have higher metabolic rates on average than people who are lean. So this mythology has kind of persisted for a very long period of time. And the idea that. Treating obesity should be about boosting metabolism has kind of persisted. And in fact, that kind of came about with one of the most effective weight loss drugs that happened around the turn of the 20th century, which actually led in part to the FDA being one of first drugs that was banned from folks. Cause it actually did boost metabolism. It also caused a lot of deaths and blindness and maybe it shouldn't be too much of a surprise later to realize that with something so fundamentally important to life as metabolism, you can't just turn it up and turn it down with a pharmaceutical drug and not expect some pretty severe side effects, including death.

Just putting aside the potential side effects for a second, if you gave a medication that boosted someone's metabolism, like a speed type medication, phentermine or something like that, would it cause people to lose weight and if so, why?

'It probably would for a while. Probably not as much as you would expect. And in fact, people have done similar studies without actually messing with metabolism. What if you just leaked out more calories? So there's a class of type two diabetes drugs called SGLT2 inhibitors, which basically make it so that you're peeing out more calories in your urine. And you can do that to the tune of 300 to 400 calories a day in your urine. And yeah, those folks start to lose weight. But they lose relatively little weight, like less than 10 pounds on average. And the reason is that it seems like, for whatever reason, as weight loss proceeds as a result of leaking out these calories, our appetite goes up. And in a very subconscious way, we end up making up for those lost calories by eating more food. Not that they are consciously recognizing this or intending to do so. It was a placebo-controlled, randomized trial. And folks who are on this drug and are peeing out all these calories and glucose are slowly, as they lose weight, cramping up the number of calories that they're eating in a very subtle and slow way over months so that they end up reaching a plateau of weight loss, again, like I said, less than 10 pounds by the time it one year mark hits.

Does our metabolism change as we age? Because I have teenagers, and you hear this as well, they seemingly can eat whatever they want and never seem to gain weight. But me? Different story.

'I know. It's really interesting. Yeah, that has been a common idea for a very long period of time. There was a very large study conducted. It was basically a cross-sectional study, meaning that they're getting people with a wide variety of ages, and they're measuring how many calories they're burning over time. They're measuring how much of their body is fat versus lean mass. Once you adjust for the fat and the lean mass, it turns out that. Until you get to very advanced ages, we're talking 70s and 80s, it looks like our metabolic rate is roughly constant once we adjust for those things. However, as you also probably know, our body composition does tend to change with age. That's after you've adjusted for the fact that people, as they age, past the age of 30 or so, are tending to lose muscle mass or tending lose lean mass and they're tending gain fat mass. And that alone is anticipated to result in a lower metabolism. Once you get rid of that effect, there's no sort of, it doesn't seem like there's a fundamental aging effect to slow metabolism as we get older.

I just want to put a punctuation mark on this point because I think there is this conceit that as we get older, you know, all these things change in our bodies and yes, they can and they do, but it's more within our control than we realize. I read this study even about runners and they found, you now, a lot of times when you're looking at data around athletes, you're look at uber athletes, elite athletes, but just for average athletes, runners, they found that in fact their speeds at which they were running a mile didn't actually go down that much between age 35 and 65 for people who ran regularly. Right, right. But a lot of times people say, well, I can't possibly run as fast as I ran when I was 35. Well, when is the last time you ran? Have you been running consistently? You know? So if you continue to do the same things that you did when you were younger, you may be able to maintain a lot of those that lean muscle mass, decreased body fat. And that is really, I think what you're saying, Dr. Hall, what is a bigger indicator of what your metabolism is likely to be? You write in the book about the popular 3,500 calorie myth, the idea that because a pound is 3, 500 calories, if you cut 500 calories out a day, you'll lose about a pound per week. Why is that wrong?

Yeah, so yeah, it's a fascinating sort of rule of thumb that's existed for decades, and it's wrong because it assumes that there's basically nothing happens inside the body when people cut calories in their diet. It presumes that the number of calories that you burn stays constant. So the 3,500 calorie per pound rule basically says that, okay, if you cut the number calories in your diet, nothing happens to the number of calories you're burning. And we just make up the difference by losing body fat. And we lose it at this sort of linear rate, kind of like if you had a banking account and you didn't have any interest fees or weren't making any interest, basically the amount that's in the bank account is gonna go up or down depending on your withdrawals and deposits and exactly that proportion. But the body does something much more clever. As people lose weight, their metabolism slows down. And as people lose weight, their appetite goes up. And as a result, this kind of assumption that nothing happens to either your appetite or the number of calories that you're burning is completely false. And unfortunately, I wish it was just like a cute little rule of thumb that was used by, you know, some weight loss folks back in the day, but this kind idea really perpetuated this myth that really small changes in your diet can lead to big changes in body weight over time. And that is really stigmatizing to people with obesity in particular. "Why can't you just cut out a soda a day? Because if you cut out soda a a day, you would lose 50 pounds in a year. What's wrong with you? Why don't you have that level of willpower?" And it just completely ignores the basic biology, which is resisting weight loss in a given food environment, and has really perpetuated this myth that people are really to blame that it's entirely within their control to kind of change these things. And there are people who can make big changes, but they need to make big change, not small changes, in order to kind lose a lot of weight and keep it off.

'So what is the answer there? If boosting metabolism is not going to lead to long-term weight loss and decreasing calories won't do it, what are people to take away from that?

'Yeah, so I think there's a couple of messages. One is that it's not hopeless, that if you can make sustained changes in your lifestyle and you have a supportive environment, supportive spouse, maybe a stable job that is allowing you to kind of shift your habits and shift your sort of local environment in ways that allow you to make those changes in a sustained way, then yeah, you can be successful. And there's lots of success stories that people can trot out on diet A versus diet B or workout. Program C versus workout program D. The problem is that most folks don't have the time, the energy, the commitment, they are undergoing life changes and yeah, it's really important to do these things, but they're doing it in the face of a food environment that has shifted to such a dramatic degree that they really have to exert a lot of individual effort and expense in order to do this. You know, the fact that we've experienced this large increase in prevalence of obesity over the past several decades is not because of a failure of willpower, right? And it's not because it changes in our genes. We need to address, again, some of the root cause of why we ended up in this place in the first place. And in particular, I think one of the things that folks are now honing in on is the rise of ultra-processed foods and how they are affecting our bodies and our appetites and our brains.

'After the break, Kevin gives us the bad and the good of ultra-processed foods. We'll be right back. I think as a general rule, ultra processed foods, if you hear that term, it's sort of a four letter word now, right? But people are like, that's something I should avoid. But what can we say about them? You don't wanna use the term addiction when talking about these foods because you don't see the same changes in the brain that you see with other addiction. Do ultra processed food though, cause you to overeat?

'So yeah, so this is a great question. And I would say the answer is yes and no. Yes and no in the way that not all ultra-processed foods are the same. Many of the ultra- processed foods that are particularly problematic when it comes to weight gain or eating too many calories also tend to have too much sodium, they tend to too much saturated fat, too much added sugar, they tend to be low in fiber and whole grains and whole foods in general tend to be low in veggies and fruits and legumes and all the things that we kind of have standard sort of knowledge about nutrition, about what makes a healthy versus an unhealthy food. And then there's a whole bunch of ultra processed foods that are probably neutral for health, right? They probably don't kind of generate problematic outcomes one way or another. And then, there's, I would argue, a bunch that are, probably, healthy for you. They actually meet the new FDA definition of a healthy food, which is kind of based on those more fundamental principles that we were just talking about. Do they have whole foods? Do they have whole grains? Do they have fruits and vegetables? All those things that we we think about as being health qualities of foods. You know, I eat ultra processed foods that kind of meet those standards for the most part, or at least I try to, but they're ultra processed because they typically are kind of microwavable ready meals and they have to have a certain amount of food technology that allows those meals to kind of heat up properly in a microwave without making them inedible after the fact. And so I think we need to kind be wary of throwing the baby out with the bathwater when it comes to classifying all ultra processed foods as things that we want to get rid when in fact many of them can be really healthy alternatives, right? Again, it's the question of what are you replacing it with? Right? I mean, if I'm replacing my lunch with one of these things, which I normally would have had a burger, right, and fries, even if they're fried in beef tallow and not seed oils, I'm going to argue that my ready meal is going to be healthier for me. Right? And it doesn't matter if my burger and fries are not ultra processed. But I think your broader question is: What is it about ultra-processed foods that have led to some of these changes that do promote overeating and weight gain, and what are the properties of many of these foods that lead to excess calorie consumption? Those were exactly the kinds of studies that we were trying to run at the NIH before I felt compelled to leave. You know, we had published an interim analysis of a study that is finishing up this summer. In the first half of the participants, we were able to kind of re-engineer an ultra processed diet that still had 80% of calories from ultra processed foods and yet people still lost weight, to a similar degree as a diet with 0% of calories from ultraprocess foods. So again, by figuring out mechanisms, we can make a lot of headway here.

Will a study like that get published ultimately?

Oh, it absolutely will get published and I'll make sure.

So there seems to be two things you're talking about here. One is weight gain, but the other is just, is there harm from eating ultra processed foods in general on your health? One of the things that people hear often is if you can't pronounce it, don't eat it. And if you flip these labels over and start to pronounce these various chemicals that are in ultra processed food, many of them you can pronounce. I mean, how do you think about that?

'Yeah, so I think, again, we have to think about who the audience is here, right? I mean, if you are a person who has the privilege and wherewithal and the interest and you have your backyard garden and your personal chef and you want to avoid all ultra-processed foods and have freshly prepared meals from scratch every day, then I don't think it's bad advice to remove ultra- processed foods from your diets. Part of the precautionary principle, right, that would be a perfectly reasonable thing to do. And so I don't begrudge those folks who say, you should just eat plants and avoid the franken foods, the things that you can't pronounce. That's perfectly fine for the privileged folks, right? The question is, we have to feed a population. We have to a population a healthy diet. We have the feed the population a sustainable diet. And the food supply has to provide that. And we have be able to feed people who don't have the wherewithal to do these things. And I'm one of those people, right. I still eat ultra-processed foods, but I use my knowledge of nutrition science to choose foods that meet my budget, that meet time commitments, that meet skill level when it comes to cooking, and use those as part of a healthy diet. But it doesn't mean that we don't have to also target the kinds of foods that are in our food supply that are generating many of the problems that we see.

You talk about this and describe it really well in the book, Food Intelligence. I really hope everyone gets a chance to read this book. It's easy to look at these issues in isolation and say, you know, a person weighs too much, they need to cut 500 calories a day and you know et cetera. But to put it in the larger context of what has happened historically, what is likely to happen in the future, what is happening with the climate. When it comes to food, you have to think about all of that. If you were on a position of power with regard to our health system in this country. With what we know now, again, we always should be researching this more and doing more studies, but with what we now, what would you do with regard to our food supply?

'Yeah, well, with regard to our food supply, I mean, I think that I would be investing a lot in, and there have been some investments, some relatively modest investments by the USDA, the U.S. Department of Agriculture, to figure out what sustainable agricultural practices might look like to still be able to produce sustainable high yields of crops. And how do we do that carefully? Because there have some countries that have tried to do this, again, without the right research. In a dramatic way Sri Lanka was one country that basically banned artificial fertilizer use overnight and didn't do the right experiments for their farmers and they saw a huge reduction in yields, food prices skyrocketed and there was a huge economic problem that resulted. In America I think we can do that more intelligently and put the right incentives in place for farmers to figure out what works and institute the metrics to make those measurements. I also think that we need to change the way that we regulate our food. I mean, the FDA has gone to a lot of expense and effort to define what a healthy food looks like. And they did that to basically make a voluntary label that manufacturers could use to put on the front of their products saying FDA healthy. Well, that's great. What if we, instead of making it just a voluntary program, what if we started to institute policies that would certain categories of foods that didn't meet the FDA healthy program and were maybe ultra-processed and maybe had other properties like they're really high in energy density or were deemed hyper palatable which might make them more addictive and basically try to tax those foods. That was the most effective Policy that reduced tobacco consumption was taxation that could be our target. And then we actually have to then support the replacements that are healthy alternatives make those kinds of ultra-processed products, the ones, those ready meals, for example, that I eat, they're a heck of a lot more expensive right now. How do we subsidize those foods? How do make them more widely available? How can we incentivize that? For example, the average U.S. Supermarket, the average diet quality of the average grocery cart that comes out of them is not meeting anywhere near the dietary guidelines for Americans. What if we incentivized grocery stores with a tax break? If the average purchase from the store met certain health guidelines. That would exert enormous upstream influences on manufacturers to improve the healthfulness of their products. There's a whole suite of, we have an entire chapter on this in the book of ideas that we could institute immediately to actually change the food supply and exert pressures on the food economy in ways that would improve the healthfulness of diets and in terms of agricultural experiments that we can do to. To really start to make these shifts that we know we have to make anyway.

Probably would make a difference not just in the short term but the long term as well which I think is was a theme that I really gathered when I was reading your book you know you know what I really appreciate about you and the book is that I think people a lot of times think of science as being like math you're gonna have two plus two equals four and you're going to be able to say that and you know and be absolutely convinced that that's the case whereas when it comes to other sciences medical science public health science certainly food science You have to lean into the nuance, lean into uncertainty of these things and challenge your long held assumptions about things. And sometimes you're surprised and I think that's what you do.

Did in the book. Right, and instead of relying on our presumptions and anecdotes and where all sorts of other things are changing and we can't really pin it down to the food, you can actually design studies. That's what science is all about.

'That was Dr. Kevin Hall, co-author of Food Intelligence, The Science of How Food Both Nourishes and Harms Us. He co-wrote the book with journalist, Julia Belluz. Thanks for listening.