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It's free and available to everyone online. Check them out at Give Weblog. Welcome to, rationally speaking, the podcast, where we explore the borderlands between reason and nonsense. I'm your host, Julia Gillard, and I'm here with today's guest, Stefan Guiney.
Stefan is a researcher and a science consultant. His background is in neuroscience. And while his PhD is in neurobiology and his focus is obesity research. So his recently published book is called The Hungry Brain. And we're going to be talking today about the science of why people gain weight, why why we see obesity rising in the US and elsewhere. So, Stefan, welcome to the show. Thanks. Great to be here.
I'll admit before we start talking that I've been kind of avoiding this topic as a podcast episode for God a year or two at least, which is not because I don't think it's interesting or important. It's just so complicated and also contentious and that those two things together are like a recipe for listeners getting mad at you because you didn't bring up a certain study that was really important or you didn't challenge a certain factual claim. And I'm sure that's going to happen.
But I basically just I don't want to avoid all topics in this category forever because of that. So maybe I should just be clear for you and especially for listeners what my goal is with this episode. I'm not going to be able to cover all of the empirical evidence stuff isn't going to be able to either, even though he knows far more of it than I do. But what I'm hoping we can really do is. Get really clear on what Steffen's like leading model is of why people gain weights and where it diverges from other leading hypotheses of weight gain and then start to talk about what evidence would help disambiguate between those theories without necessarily being able to actually cover all of the evidence.
Does that sound good? Great. All right. Well, then let's jump in.
Stefan, what's your sort of overview of why people become obese?
Yeah, so this is a really complex topic and I think we have to find some way to get a toehold before we can, you know, some way to get a toehold on the causal chain before we can start really trying to dissect what the ultimate causes are. And I think one really good way to get a toehold is to just look at it from thermodynamics perspective, which is that you can't accumulate energy in your body unless you have a higher rate of energy entering than the rate of energy that's leaving your body.
And so I think that's a useful starting point, although certainly not an endpoint for thinking about how obesity develops. So it requires that we are ingesting more calories than we're spending. And so I think at that point you can start thinking about why are we ingesting more calories than we're expanding? And so how do we get calories in? We eat food, how to calories, leave our body metabolic processes, as well as work performed in physical activity and things like that.
And so I tend to look at things from the perspective of the energy inside of the equation because basically you can out eat almost every level of energy expenditure.
So no matter what your physical activity level is, or no matter what your metabolic rate is, it's almost always possible to out eat that. And so I tend to think about it as a question of how much are you eating relative to your energy expenditure?
Well, just on that point, even though it is possible to eat like two to undermine whatever caloric deficit you built up with exercise. For an obesity researcher trying to study why obesity has gone up over the decades, wouldn't it be more relevant to look at whether rates of energy expenditure are enough to explain the decline in energy expenditure is enough to explain the rise enough?
Absolutely. And I mean, there are people who are looking at it from that perspective for sure. And and I'm not trying to say that energy expenditure is not relevant, but I mean, if we look at the history of calorie intake in calorie expenditure in this country, what we see is that for most of the last hundred years, people have been able to roughly match calorie expenditure with an appropriate calorie intake. And so if you look at calorie intake, one hundred years ago, it was actually pretty high.
It was almost as high as it is today. And yet there was very little obesity. And presumably that's because almost everyone was working manual labor jobs. We didn't have barely had any automobiles. There weren't washing machines, there weren't automatic dryers. We were doing a lot of things that required physical effort, building things in factories, milking cows, weeding the fields.
But what you see over the course of the next 40 or 50 years in the United States is that our calorie intake actually declined. And that was you know, it's kind of what you would expect. In the sense that people were not working up as much of an appetite as things were becoming mechanized and their physical activity expenditure was declining.
What time period is this roughly? So we when the USDA first started tracking calorie intake was in nineteen eighty nine, and that's when calorie intake was relatively high. And then it declined through about the 50s and 60s. And then it started to rise again in the late 70s, early 80s.
So energy expenditure and energy intake started declining in the middle. Yeah exactly. And then intake started going back up but energy expenditure did not. Right. And so well it's not quite that simple, but it never is. Yeah, I know. I'm sorry. I'm trying to clear. But basically the point I'm trying to make is that there is a relationship between calorie expenditure and calorie intake that is under ideal circumstances is maintained non consciously by circuits in the brain.
So there's actually a regulation that's happening that's trying to keep body fats in at the right level. So you see this kind of coupling of energy intake and energy expenditure and then around nineteen eighty, those things decoupled. So you see an end, by the way, it wasn't quite as sudden as that. It started earlier, but in the 1980s, eighties, it really accelerated. You see this decoupling where energy calorie intake is increasing fast and calorie expenditure, at least in terms of people being physically active, is not increasing proportionally.
And that's when you really got the obesity epidemic. So this this is why I tend to focus on calorie intake, is because for any calorie expenditure, there is an appropriate calorie intake. But really, it's one of those things decouple when calorie intake becomes disproportionate to expenditure, that you start getting problems with obesity and so on. And so this this comes back to the question of what is obesity or what causes obesity. And obesity really has to kind of fundamental characteristics.
And this is something that's been pointed out by my mentor, Mike Schwartz, at the University of Washington. And that is, first of all, you have developed due to this imbalance between intake and expenditure. But the second is that you actually have a change in how the brain regulates body fatness and how the brain regulates the amount of energy that is coming in. And so you have essentially the brain, instead of defending a lean state, it begins to defend an obese state and against changes.
And the way that it defends a lean or an obese state is in terms of the the appetite or the urges that it gives you to to eat or to stop.
Yeah, yeah. Basically it yeah, exactly. It activates nonconscious circuits that are going to drive you toward food via hunger and increased cravings and things like that to in order to maintain that higher level body fatness. And so that's why weight loss is so hard, is that once your brain is defending that higher level of body fatness, if you try to lose weight, your brain's like, no, this is not what I want to do, just the same way that a lean person losing weight, they would have increased hunger, increased cravings, et cetera.
And so and so those are the kind of fundamental two characteristics of obesity, is you have this thermodynamic change of energy flux and you also have this neurobiological change of defense of that higher body fatness. It's not just the state that results from passive overeating. If it were, then you could just eat less and it would be easy to lose weight weight.
So you're saying, hey, we're eating more than we used to relative to our expenditure and be our brains want us to eat more? Is that are those really separate things or does the first thing just follow from the second?
Well, OK, so I feel like I'm not giving you all the context that you need to add more context. Basically, we can conceptualize of eating behavior in two different ways. There is eating behavior that is due to circuits in the brain that are trying to regulate your energy intake like. Hunger, and then there are circuits in your brain that are kind of independent of trying to maintain your energy status like things that make you crave really delicious foods, like you don't eat a big fat slice of chocolate cake at the end of a meal because you're still hungry.
There's not like an energy need you're trying to fill by eating ice cream or drinking beer.
The thing that we used to say in my husband, me and my brother were kids was after we'd said we were too full to finish our dinner and then could we please have dessert? And our mom would be, like you said, you were full. Why do you want to serve? We'd say, well, my dinner, too, was full, but my dessert to is still empty. And then she would laugh and give us dessert, not because we made a good argument, because it was funny.
Yeah, we got reinforced for it.
Nice. Yeah. So basically. So coming back to this question of what causes obesity, I mean, there is there are a bunch of things that make us eat more relative to our calorie expenditure. We don't have very high calorie expenditure needs in modern society. But there's also something that is changing the way our brains work that cause us to actually defend that obese state and make it very difficult to lose weight.
And just to illustrate that a little further, I think an example that really helps is to talk about the biggest loser. So people a lot of people are familiar with this show in case any of the listeners aren't. It's you know, they they get people to lose enormous amounts of weight. It's a competition to see who can lose the most. And then there's this really big money prize at the end. And so researchers have actually followed up on the people who lost these massive amounts of weight.
One hundred plus pounds on The Biggest Loser. And they tend to regain most, if not all, of that weight in fairly short order after the show. And that's not really what you would expect if body weight were not regulated, if there was not some change that occurred or some difference in the way that these things are regulated between someone who's obese and someone who's lean because they are gaining weight at a much faster rate than you would expect for someone who started off at that lower body weight.
So someone who starts off lean and tries to stay lean, it's going to be a lot easier than someone who starts off obese, becomes lean and tries to stay there.
But why? Why couldn't we just explain that? That data by saying, well, maybe they started out lean when they were very young, but then it's like high calorie of food is so available that there was just always a temptation to to eat more calories than they were burning. And so, yes, they lost the weight when it was sort of part of this, you know, program where there was discipline being imposed. But then when that's over, assuming they just go back to the exact same environment and the exact same behavior they had before, of course, they're going to regain it because they had a surplus.
It's just not clear why we need to invoke any kind of set.
Yeah, yeah, sure. I mean, I think that what you're saying is probably part of the explanation, whatever your habits are or whatever other things like that are going to be things that it's hard to reset, even if there's no set point.
However, there's a lot of evidence independent of that, that there is this regulation of body fat levels and that that does regulate around a specific preferred level. So we know that if you so there's a researcher named Rudy liable, for example, who's done a lot of this work. If you take people who are either lean or obese, basically the same either way, and you get them to weight reduced by 10 percent, you see very profound changes in their physiology and their brain response to food cues.
And so what you'll find is that they will have a decrease in their metabolic rate that is disproportionate to the amount of weight that they lost. So it's not just because their bodies are smaller, but there's actually this starvation response that kicks in that actually conserves energy, even beyond that, to try to regain the lost fat. And that also has a neurobiological correlates where you can put people in an MRI machine and you see that basically all the brain structures that are responsible for making us crave food light up like a Christmas tree after the weight loss.
And also you find that when you give them food, the same amount of food is less satiating after they have lost weight. And we know a lot about the mechanisms underlying this. And this is why I'm so confident about this, is that we actually have a really good picture of how this works. And it relates to a hormone called leptin that's produced by fat tissue. And that is a signal to the brain of how much fat is in your body.
And when a person loses weight, their leptin goes way down. And that's really the key signal to the brain that causes that so-called starvation response that tries to bring the body fat back. And the reason we know that that's the key signal is that if you replace leptin back up to the pre weight loss level, you don't get those response.
So you can just add leptin. You can just add, oh, why aren't we all doing that?
Just seems like that's a really good question. So I think there's a couple different reasons for that.
And one of them was, is that when leptin was first discovered, it was thought of as this like incredible potential miracle weight loss drug. And it was very clear that it played a really important role in body fat regulation.
There's like almost a century of research leading up to the discovery of leptin.
But basically, when you just take people who are overweight or obese and you inject leptin into them, it doesn't really do anything. It doesn't cause them to lose weight.
And so basically what they figured out is these people already have high levels of leptin and increasing those levels further. In other words, telling the brain, well, actually, you have even more fat, doesn't really tell the brain to eat less. So leptin is more the brain is really responsive to decreases of leptin as a starvation signal, but is not really responsive to increases of leptin as an access signal. Right. I know it's frustrating and you have to think about the evolutionary context as is a plausible explanation for that.
Obesity is just not observed among hunter gatherers and it's just not an issue. So basically, you have this huge disappointment in the pharmaceutical industry that put leptin on a shelf for a long time. And and I I'm not sure that it's ever really recovered from that disappointment. And I'm not sure if anyone is really looking at. To it for weight loss maintenance, but they're not it's not about causing weight loss, it would be about keeping weight off. Exactly.
So you'd have to lose the weight and then it would help you stay there.
And I don't really know if anyone is looking into it, but it's certainly a really plausible idea.
There are also some practical issues. Well, aside, for a minute, we kind of we kind of skipped over this elephant in the room, which is you started talking about how there's some change to our brains at some point in the later mid or later part of the 20th century that caused our brains to want to defend higher weights than we had before. What was the change?
Yeah, I mean, that's a really, really good and really tough question. And I don't want to give you the impression that we understand it very well because we don't there's not really a lot known.
I mean, we know that if you overeat calories, you'll gain body fat, but that doesn't necessarily increase the defended level of body fat. So if you overfeed someone and they gain fat and then you stop over feeding them, they will lose that fat usually. So it doesn't really mimic what we see in actual obesity, where people's set point really resets to a higher level, like turning up a thermostat.
And so the research that I did in that Mike Schwartz did when I was in his lab and that's ongoing, is looking into one possible mechanism for that.
And what we found is that there was actually this inflammatory process occurring in the hypothalamus, which is the part of the brain that regulates body fatness and receives that leptin signal. And it turns out from other groups as well that this is part of a generalised stress response that occurs in the hypothalamus of animals that are becoming obese. And and there's increasing evidence that it's actually plays a causal role.
So if you can prevent that inflammation from happening in the hypothalamus and these other associated stress response changes, you can actually attenuate the fat gain that occurs in experimental models of dietary obesity.
And we actually were able to extend that into humans as well, at least observationally using non-invasive MRI technique with my colleague Ellen. Sure, she was the one who led that research and she was able to demonstrate that people who have obesity actually have MRI signals in their hypothalamus that look a lot like they are also inflamed. And so the more signal you have in your hypothalamus that looks like inflammation, the higher your body and level is likely to be. So and again, I say that I want to emphasize that we don't know all the details of how this happens.
And another really important part of this that we don't understand yet is what causes that inflammation. That's obviously a key question. I can give some general information. I mean, we know that when we put animals or humans on certain types of diets, they tend to gain weight. And it also tends to produce this inflammatory response. But what kinds of diets?
So those they tend to be refined, palatable, calorie dense diets.
And by palatable, you mean like tasty. Yeah, exactly.
Diets that are motivating and that animals will tend to eat. A lot of humans will tend to eat a lot of.
Is there. Are you using motivating and palatable as synonyms or are those different things? Those are different things.
And it's actually it's actually kind of sometimes tough to talk about with the general audience because the concept of audience is special. Go ahead and give it a shot. All right. So the concept I'm really trying to get at is this concept of reward, which is a which represents three things. It represents motivation, pleasure and learning, reinforcement learning. And the really the main part of that that I'm referring to is the motivational component. So the what is your motivational level to eat?
Because honestly, it doesn't really matter how much you enjoy food. What matters is what your motivational drive is to eat that food in terms of the consequences. So like, for example, to separate those concepts a bit, there are some drug addicts who don't actually derive pleasure anymore from the. Drug that they're taking, but they still crave it strongly, so that would be strong motivation, Willow. Pleasure or palatability and I guess low I maybe high reinforcement reinforcement is just how much each time of consuming the thing causes you to want it more in the future.
Yeah, exactly. So, yeah. So it's still be strongly reinforced. Got it. Just so pleasure. Yeah. And I think there are some foods that I actually get a lot of pleasure out of, but I just never crave like apples, for example, every time I end up eating an apple because there's nothing else around them like oh I forgot how good these are and I just never want one again in the future. Interesting. Interesting.
Yeah. I mean, those things in everyday life tend to be fairly closely linked to one another. But I mean, you can come up with examples where they're not that closely linked. Yeah. Sorry I said I've sidetracked you, but we were talking about theories of what causes the inflammation that we see. Yeah. Memory that is associated with like the drive to consume more calories than one is expending. That's right. Are associated with obesity. Are saying that would be a better way to put it.
So and we don't really know what causes those things, but we do know that certain types of diets cause that we don't know exactly what it is in that diet. And there are theories like some people think it's the saturated fat. Some people think it is the lack of fiber that causes changes to the gut microbiota that then has effects on the brain.
But it all goes through the brain. You're saying, yeah, it has to go through the brain because ultimately the four for a couple of different reasons.
First of all, the brain generates all of our behaviors, including our eating behavior. It generates all of our feelings and impulses that influence our eating behavior as well as our physical activity patterns. It regulates a lot of things about our physiology as well, including our metabolic rate. Not to say it's in complete control, but it influences. And furthermore, the body fat regulation system, that measure of your body fatness and influences appetite and metabolic rate in order to homeostatic regulate body fatness is located in the brain.
So the brain is a really very central to all of this.
OK, and so whatever whatever it is in that in this diet that causes that's like extremely rewarding and that seems to be associated with inflammation and obesity. That kind of diet started becoming more common in the mid to late part of the 20th century.
Is that. Yeah, I mean, and, you know, because of the uncertainty that we have about the exact mechanisms, I can only really paint this in broad strokes. But I still think the broad strokes are really useful. If you look at animal models of obesity, the absolute most fattening thing you can possibly give to a rodent, for example, is to give them a variety of highly palatable human junk foods. I mean, literally, these things are human junk food is insanely fattening to just about any species.
And by fattening, you mean because they're motivated to eat a lot of it. And also it's high calorie?
You know, that's a good question. I it's definitely related to that. But at least in rodents, I'm not sure that's the full story. You actually see also calorie expenditure effects. And what I mean by that is, at least in certain contexts, what you'll see is that they actually burn less energy than they should on those diets. So it's not quite that simple in rodents, although in humans you really see a lot more effects on the energy inside than on the energy outside.
So you don't have people who have obesity, have a higher level of calorie expenditure, higher metabolic rate than people who are not obese, just not high enough to make up for the surplus.
Correct. So they consumed. Yeah, exactly. So they have larger bodies that require more energy and therefore they generally have a higher metabolic rate when correcting for things like gender and height and that sort of thing.
How does this model that you've laid out interact with the sort of simplistic calories in calories out model where people like? I know there's a lot of the debate over what causes weight gain is over, whether the calories in calories out model is correct. And, you know, there are people stated in different ways. But one way people state it is like the only way you're going to gain weight is if you're consuming more calories than you're burning. And anyone who tells you differently is selling something basically.
Is that is this just a specific version of the calories in college or is it a different thing?
Yeah, that's right. So the the idea of calories in, calories out, I think. Wires defining because it's used in different ways, in different contexts. And so one of the ways is the way that you just said, which is that the balance between calories in and calories determine the amount of fat that you carry. And, yeah, that's almost not different from the first law of thermodynamics. I mean, that's not in question. Even though some people would debate it.
That's not a serious argument. But there's this other idea that some people refer to, and that is really that, that your level of body fat is determined exclusively or predominantly by voluntary decisions that you make about how much food you're eating and how much you're exercising. And so this is the idea that basically there's no regulation happening. There's nothing trying to, you know, keep you from losing weight. The only thing that's keeping you from losing weight is poor decisions, basically.
Poor willpower. Yeah, willpower. Poor voluntary decisions. And I mean, there's no doubt that will power plays a role.
Like if you can't if you have a craving to eat something super unhealthy and you can't stop yourself from doing that, of course, that's going to increase your risk of gaining weight. But I think what the calories in that version of the calories in calories out idea misses is that a lot of the things that drive us to eat and that determine our eating behavior are not voluntary conscious processes.
And I mean, ultimately, we have a conscious gatekeeper over our eating behavior. You can say, no, I'm not going to eat this, but when you have impulses arising from non conscious parts of your brain, like hunger and cravings and those sorts of things telling you to eat, we have a limited capacity to control those things.
If they're if they're being thrown at us all all the time, day after day. And usually those types of impulses are going to be more influential in people's everyday eating behavior than the kind of conscious, rational or willpower or whatever, however you want to call those higher order circuits.
So maybe a way to distinguish would be to ask you. Is is there anyone who thinks that if you could take people who are obese and put them in a controlled environment where you're feeding them a controlled diet and they wouldn't gain weight or they would gain weight very slowly, I'm trying to distinguish between models where the the causal arrow that eventually leads to weight gain goes through the node of like. Consuming food like calories consumed and whether you're like whether we want to call that free will or or us responding to sort of drives that are very difficult or almost impossible to resist, it doesn't really matter.
But it's like the act of putting food in your body is essential to how much weight you gain. Versus on the other hand, theory is that that there's something about the way our body is processing the food that we consume that is like maybe more efficient or something like that that is like really not couldn't possibly be called a choice because it's just something our body is doing. And that is the thing that's causing people to be more likely to be obese now than they were 50 years ago.
I mean, there are differences between individuals and how the body deals with food. There's no doubt about that.
Yeah, but we're looking for a difference. Like presumably there have always been differences. And so if people are more obese now, then there must have been something that changed unless the genetics just changed that much in 50 years.
I mean, the the problem. So basically, the answer has to be either in the calories inside or in the calories outside or both. And calories out also involve how efficient your metabolism. Yeah, absolutely. Absolutely.
So what I'm trying to say is that the difficulty with the calories out argument is that people who have obesity almost invariably have higher calorie expenditure, not a lower calorie expenditure. And so you can't really explain obesity by saying they have a reduced calorie expenditure because they don't they have a higher calorie expenditure. So the only way you can really explain it thermodynamically is by saying the calorie intake is higher. So then the question becomes, why is the calorie intake higher?
So does that mean that the puzzle of why there's more obesity now than there used to be reduces to the puzzle of why are people consuming more calories than they used to?
I am not sure I would quite endorse that statement.
I mean, I think that clearly, if our calorie expenditure, if it clearly if all of us were jogging two hours a day and eating the same amount of food as we are right now, there would be less obesity. So I don't want to say that there's no role for calorie expenditure, but there has been there has been a decoupling of intake from expenditure. So our intake today is, you could say, inappropriate for our level of calorie expenditure.
All right. So, yes, OK, so. Let's talk about other common theories of weight gain that have to do with the kind of food that's being eaten. I mean, you talked about this a little bit because you compared the, like, super high rewarding modern diet that has like pizza and ice cream sundaes and, you know, refined white bread and cookies and things like that compared to diets in the past that were less rewarding and maybe somewhat less palatable.
But there's a bunch of other theories of what causes weight gain. Get more specific about like. Some calories being good, say another calories, maybe not so good or even bad. How does how does your model differ from those?
Yeah, I mean, I think as far as we currently know, if you really look at the most tightly controlled state studies available in humans, of which there are a number as far as we currently know, the calorie value of food is the only food property that meaningfully impacts body fatness. So there are a number of studies that have varied to other things, like the carbohydrate to fat ratio, varied things like sugar intake, even varied protein. And there are many, many other hypotheses that you could test about how food composition affects body fat and that haven't been tested yet.
But in terms of the basics like macronutrients, it doesn't have any effect. It's independent of calories, as is what the current evidence suggests. And so we don't really have any evidence right now that things other than the calorie value of a food impacts that food that foods effects on your body fat. And so basically and we do actually have pretty good evidence that the macro nutrient composition, that is the fat, carbohydrate and protein composition does not affect body fat independently of calories.
And so that's not to say that some foods are not more fattening than others. I think that some are. But I think that relates more to the fact that we tend to eat more calories of some foods, right?
Yeah, I'm very confused by what people mean when they talk about a food being more or less fattening. Like how can you even talk about that independently of the amounts consumed?
But I don't think you have to talk about it independently of the amount consumed. I think that's an integral part of it. So, like, if I put or let's say you put pizza in front of me versus like a piece of fish in a salad and a potato, I'm going to just in real life, I'm going to end up eating more calories of that pizza, probably vastly more calories than I would of the fish and, you know, potato and vegetables.
So then if we talk about how fattening one food is relative to another, we're talking about if given the option to eat as much as we want of food and versus food, be the total amount of weight we will gain as a result of the amount we choose to eat. A food A is higher than food. Therefore, food is more fattening. Yeah, basically. I mean, and and first of all, I don't want to say that I don't want to express one hundred percent confidence that there's nothing besides calories that could possibly matter, because there are a lot of things that we just haven't tested yet.
Like the effects of different types of fibers, the effects of palatability persay or reward value food for say, like for example, let's say that you have a diet that's very similar, except one version is highly rewarding and the other one is kind of bland.
Does that have does that influence how much fat you would gain from the same number of calories, perhaps via effects on these brain circuits that regulate your metabolic rate?
So we don't really know the answers to those questions. And there's like a million little sub hypotheses that you could ask that we haven't asked yet.
Furthermore, in animal experiments, it's not as simple as it is in humans. So in rodents, you don't just in rodents, it's not just about how many calories they eat. Food actually does have a more important impact on their calorie expenditure.
But so eating one hundred calories of food A would cause them to just be be motivated to exercise more than eating one hundred calories of food.
B It's not necessarily via exercise that can also be bought via just normal metabolic processes. And so but sometimes they don't really differentiate. They just know that these animals gained weight when we put them on this refined, calorie dense diet, even though they didn't actually eat more calories than this other group. So that implies that they're burning fewer calories. One thing I realized I didn't get clear on earlier is. If eating this high reward diet is causing our brains to to regulate the amount of fat in our body, to make us want to eat more to to maintain a higher weight, is it the rewarding ness of the food that's causing that change or is it the amount that we're eating causing that change?
So, for example, if we took two people or look, let's say we took one person, we caused them, we forced them to overeat, but eating bland foods, not rewarding. They're just eating because we're making them and they do this for several weeks. Do they now do their brain now have a higher set point where it's going to try to make them maintain a higher weight even when we stop holding a gun to their head? So these experiments have been done in animal models and to some degree in humans experiments.
To ask this question and to clarify the thing I was implicitly meaning to compare that to was someone who. I guess this isn't an obvious comparison, one could compare that to a person who ate an amount of calories that was enough to just maintain their weight, but they were all rewarding calories that they're eating, you know, two thousand calories a day or whatever the recommended amount is. But it's all pizza and ice cream and things like that. Which of those people, like the first person who was overeating, bland foods, or the second person who's like appropriately consuming the amount of calories but rewarding foods?
Which of them or both would would end up messing up their set point? Yeah.
So the I think the first with that this was addressed in is in animal studies, in rodents, in rats in particular. And what they showed is that if you take two groups, one group or let's say three groups, one group that gets to eat as much as it wants of some really, really awesome, delicious food, gets really fat really fast.
And then you have another comparison group eating healthy diet as much as it wants. It stays lean. And then you have a third group that has a restricted calorie intake of the really delicious food. So it's being restricted to match the level of body weight of the group eating the healthy food. So it's not gaining weight, it's being restricted, but it's eating that the same food as the other group that's getting really fat. That's my person. Be right.
And so after a little while, you say, all right, well, now you can eat as much as you want. And what you see is that that group that was previously restricted rapidly bounces up and approximates the curve of the group that was eating that food the whole time. Whoa.
That's really weird, because that that makes it sound like our brains are picking a set point based on not on how much we are eating, but on how much we would want to eat of the food we are eating and how much and how you know, how much we would weigh if we were eating the full amount that we wanted to of the food available.
That's absolutely right. And I think it's creepy.
Yeah, I got to say, this relates to some other things that we can talk about, but it's basically the brain places the brain values food instinctively or non consciously based on its physical qualities that are evaluated by the gastrointestinal tract in the brain. And so it places a certain value on foods. So foods that are really high in fat, sugar and salt and protein, whatever brains like this is really good. We got to get a bunch of this because that's the stuff that helped our ancestors survive.
But if you and so what I think is happening is that essentially when the brain is in an environment where it can get a lot of this food that's that it's finds valuable, that instinctively it finds extremely valuable because it's really calorie dense and high in these properties at once. It basically facilitates the consumption of this awesome food by increasing by by affecting these circuits that are regulating your appetite and body fatness and shifting at all upward to allow you to consume more of this awesome food while it's around.
So does this does this theory mean that whatever my highest weight is, that I lay my weight fluctuate throughout my life, whatever the highest weight is? That's the way my body is going to want to stay at the rest of my life or no, because that implies that the set point is based on weight. It's not based on kind of food I'm eating.
So it is both.
So if you take those same animals and so so this this is what this is another thing that I think is really important is the set point, the the kind of level of body fitness at which your brain's going to defend the level of body fitness which your brain is going to defend is context dependent. And so I think this is the part that makes the conversation go from seeming hopeless to hopeful for people who carry excess weight. Is that so? Let's let's go back to that experiment I was describing.
You have these animals that they're, quote unquote preferred weight or defended body weight is dependent on which diet they're on, not how many calories are currently eating.
And but if you take those animals that have gained a bunch of weight from eating this really awesome, calorie dense, delicious food, and you switch them back to a healthy diet, a lower calorie density, unrefined diet, they will spontaneously lose weight even if you let them eat as much as they want.
So their set point actually changes can actually go back down, even if it had gone up and so on. Then I think you see the same thing. And people like not everyone who diets does so by forcing themselves to eat smaller portions. Sometimes when people change their diets in ways that are qualitatively better, like going from a refined, calorie dense junk food diet to a lower calorie density, healthy diet, that's fresh vegetables and meats and fruits and whole grains and potatoes and things.
You will see that people will spontaneously lose weight, their appetite will spontaneously decrease, and they without trying to restrict their calorie intake, even if they're eating the fullness, you'll see that typically people will be able to lose a certain amount of weight comfortably without having to fight themselves. And I think it's it's the same it's probably the same phenomenon that you see in the animal experiments when there are controlled experiments in humans that have suggested similar things. There was one that I think is interesting on this topic where they gave people this bland liquid shake, basically, and they said this is all you have to eat for the next two weeks.
And they lost, I think, like, were they allowed to eat as much as they wanted to? Yeah, yeah. As much as they wanted. And they lost like seven pounds. They just weren't eating that many calories of it. And they were told eat to you're not this is you're not depriving yourself. Just eat the fullness. And they lost about seven pounds. And that's what people tend to do when they go on really bland, repetitive diets.
They don't feel as hungry. They don't eat as much the way they I don't know, the study didn't report that. But your model would predict that they wouldn't be there at that point was was lowered by eating bland food. My model would predict that they wouldn't as long as they stayed on the bland diet. But as soon as they go back to their normal diet, my model predicts that they would bounce back up. Yeah, so that's the catch.
But to to finish my thought, they had another group of people that they asked to lose the same amount of weight over the same period of time by just applying portion control to their habitual diet. So it's like you're going to eat the same foods you always eat, you're just going to eat less of it to match this weight loss curve of this other group. And what they found is that the group that lost weight by portion control was ravenous. They have very, very different responses.
They were they reported in the study that the people were very uncomfortable.
They were dreaming of food, whereas and they had I'm not going to go into it because it would take a long time to explain. But they had some more physiological measures of hunger drive. And basically what they found was that people who lost weight on the bland diet weren't any more hungry. At the end, people who lost weight by portion control were super hungry and their food motivation kicked in so that starvation response was activated in one case, but not the other, presumably because, you know, the set point had changed.
Well, I mean, I know this is just one study in the context of many studies, but if I was just looking at this study, the way I would interpret it would be to say presumably the diet they're eating normally. Is is more calorically dense and less filling, and so I would expect them to be less full eating the same number of calories as the boring Sheikh group, because they're their food is less filling than the sheikh would be. And also, I mean, the tastiness of the food is just salient.
And, of course, your cravings are going to kick in when, like, your your you were just eating a donut and like now you want more donut as opposed to if you haven't looked at a doughnut in weeks. So would you say that that and that model doesn't rely on set points at all? Would you say that is consistent with the data? And the reason you're interpreting it differently is just because of other evidence you have about set points, or am I wrong about it being consistent?
I'm trying to think this through here. Potentially, I would have to go back and look at the study design to see if it would be possible to exclude that interpretation, to leave out some points.
You mean and and still explain it.
No, no. To rule out my job. Yeah. Yeah. Because and again, the some of the measures that they use are a little bit too complicated for me to explain efficiently right now.
But I think it would depend on when those were done, if those were done right after a meal, when there could potentially be differences in satiety, then perhaps if they were done first thing in the morning, like these types of tests often are where you haven't eaten in a long time, I wouldn't think it would be influenced by a recent meal.
Yeah, I mean, I still think about my breakfast for hours after I get it and it good. But no, that's that's a fair distinction.
But yeah, I mean, it definitely integrates information from other lines of evidence as well. My belief. Right. Yeah, that makes sense.
A number of I'm sure listeners will be curious about how your model explains the fact that specific diets like low carb diets, for example, seem to be pretty effective in causing people to lose weight. Is that is that just a would you just explain that to success by those diets being less rewarding? And therefore, I think that's part of it. And by the way, I want to I want to clarify something. I want to I want to say that we're calling this my model.
But this is really a model is not something that I came up with for the most part. This is something that I am that is taken from the scientific community, including me, that I'm trying to communicate, not to say that every scientist know everything that I say. But, yeah, I don't want to I can't take full credit for this. And I want to say that within my field, most of what I'm saying is pretty commonly accepted.
What do you what would you say is the distribution of use it would it be like, I don't know, 90 percent of people researching obesity, like basically just agree with everything that you said and, you know, 10 percent think it's insulin or.
I think that I don't know that I would say I wouldn't I wouldn't want to claim that 90 percent agree with everything I say. But I think in broad strokes, almost everyone in the research community would agree that food fraud plays an important role in obesity. So I would put that at at least 90 percent, just that big idea.
So what are the main disagreements then?
I don't think there is a huge amount of disagreement, to be honest with you, within the scientific community.
So all this controversy that I encounter is just among outsiders for the most part.
I think I think the scientific community there, people are siloed. So they're not necessarily they may not have strong beliefs about what somebody else thinks is causing obesity. And they tend to say, well, it's probably a lot of things coming together that's causing obesity with all of those things converging through thermodynamics. Right.
OK, so then back to the question you were trying to answer for me a few minutes ago about explaining the success of, say, low carb diets. Yeah, yeah. So I personally and I don't want to suggest that this hypothesis has been tested. This is just my belief based on other evidence. I think personally that the reward concept can at least partially explain the success of low carb diets, because, again, I mean, the human brain is wired to seek certain properties and food, things like starch and fat and sugar and salt.
And those are things that. Basically, the brain wants as much as possible of all of those things all the time on his own, a certain nonconscious impulsive level, so restricting any one of those things, saying, well, I'm going to completely cut out carbohydrate or I'm and completely cut out fat, you're basically providing a diet to the brain. You're providing a palette of foods that is less desirable to the brain in terms of your brain's intrinsic motivation to eat.
And so I think that's part of it. And I think that really explains why. You see people offers at least a partial explanation for why you see people losing weight on diametrically opposed diets. So you see low carbon and low fat, for example. Yeah, people lose similar amounts of weight.
Well, that is an interesting question and it depends on how you look at it. So, first of all, I will note that people, whether or not in amounts are similar, people do lose weight on both, which implies that it's not as simple as saying carbs are fattening. And the more you eat, the fatter you get.
And I suppose for some people, carbs could be more rewarding than fat and for others the other way around. I think that's right. I think there is a huge amount of variability and people clearly do respond differently to different types of diets. But the other other point I want to make is there are a lot of randomized controlled trials that have compared low carbohydrate to low fat diets. And generally the low carbohydrate diets cause more weight loss, although they both cause weight loss.
But when you really start to dig into those studies, it the answer becomes less obvious than it seems on the surface. And the reason is that if you if you really look at the low fat diets that are typically used as a comparator, they're really, really wimpy, low carb, low fat diets has that. They're not very low in fat. First of all, they're usually not as low and fat as the low carb diets are, low low carbs.
And second of all, they tend to be based on this kind of antiquated concept of low fat diets where only the low fat matters and you don't care about any other aspects of quality, often replace the fat with sugar. Yeah, it's like a snack. Well, that's exactly what I was thinking of that. And so, I mean, what does it mean for low carb to be more effective than that? So now increasingly you have more studies that are coming out where people are starting to care more about diet quality and about matching diet quality between the arms.
You should really. Here's how I would do it or the right comparison. My view would be take a certain calorie threshold and then let people design the most palatable diet possible under the constraint of that calorie limit and a certain carb limit. And then similarly, a calorie, the same calorie limit and the same fat limit design, most palatable diet. You can then compare those head to head. Yeah, of course it would be different for different people. So then that's hard to do in ice cream studies.
So it doesn't work so well. But yeah. Yeah, they're really complex hypotheses to test sometimes. But if what you see in these more modern studies that are caring more, paying more attention to matching the conditions and focusing on diet quality is first of all, improving diet quality gives you better effectiveness. That focusing on diet quality, I should say, gives you better effectiveness than not caring.
You get better weight loss and caring just in any way. Basically what I mean is the quality aspect matters independently of the macro nutrient aspect. So and by quality here, you mean like by quality, I'm talking about the degree to which diet is kind of refined junk food. Oh, I see. Yeah, yeah, I got it. And so when you focus on diet quality, you get better results. And what you also see is that there's not there's often very little or no difference in the weight loss response you see between low fat and low carbohydrate diets.
And in fact, there was a recent study that came out from Chris Gardner's group that was actually funded by the Nutrition Science Initiative, which is this organization headed by Gary Taubes, who is a big proponent of the idea that carbs are bad and fat is good. And this one showed exactly what I just described, that there was no difference when diet quality was high in both the low fat and the low carb arm. Both arms lost a pretty good amount of weight and there was no difference.
So I think the kind of like there's this kind of received wisdom that we have that low carb is more effective than low fat weight loss for weight loss. But I think that emerging evidence is suggesting that that might not be quite as straightforward as we thought it was, as I thought it was as well. But I think it's very individuals. You know, there are big error bars on these results. Like you see, you put people on any kind of diet.
You're going to see a range of responses that ranges from really, really impressive weight gain all the way, weight loss all the way to weight gain.
And I mean, all you have to do is look at the standard deviation of these measures and you can see that there's a huge range of responses. And so it's very individual. And I think whether one diet is superior to another in an average sense may not be exceptionally informative with respect to how an individual will respond to a diet.
So I know that your your book goes into this in much greater depth than we're going to be able to in the last two minutes left.
We're already actually way over the time that I had expected to spend, but that's fine. But the other sort of elephant in the room is the like, great. What do I do about this question? I imagine many people are thinking like, OK, so is is the answer. I just have to stick to a completely bland and unrewarding diet. And when I go off it, even briefly, then suddenly I have increased my set point and my body is going to try to make me obese like.
Is I mean, maybe these low carb, low fat diets that we were just talking about are like a compromise, there's like somewhat less rewarding.
Yeah, yeah. And, you know, I think I've probably given people the impression that I'm a little bit more of a drill sergeant about food reward than I than I really am. But I mean, what food reward is, it's a tool that you can use to achieve whatever your body weight goals are, among other tools. It's not the only tool that's available to us. So you're eating your brain.
Are you being an individual? OK. Yeah, but I feel like what is the thing I'm fighting against? Like I have goals in food or what is getting in the way of those goals. It doesn't feel like a tool to me. Well, what I mean is it's a tool in the sense that understanding how it works can. Oh yeah, you can you can you you can lower it in order to lower your food intake it. But there are other tools that can work.
I mean, eating a diet that's lower in calorie density is something that is at least partially independent of that reward factor. Then there's physical activity, there's stress management or sleep management. So, I mean, you could theoretically put together a slimming diet and lifestyle that is not any that doesn't have reduced food reward. That said, you are leaving tool on the table that you could be using.
So but I think one thing to keep in mind is that, like, you don't necessarily have to eat a completely bland, uninteresting diet to achieve your your goals. I mean, personally, the balance that I like to strike is I like to focus on the natural flavors of high quality unrefined foods. And so a really nice fruit, a really nice vegetable, a really nice piece of meat, really nice eggs, potato, you know, with nothing on it.
You don't really here.
But do you see what I'm trying to say, though? I mean, it's there it sounds like for you, unrewarding food is less frustrating than it is for many. Well, that's that is possible. That is possible. I mean, we have our expectations set by living in a society where we're used to having our palates constantly entertained. And so that's part of the problem. But I mean, what I'm trying to get at is there's a difference between getting reward from eating French fries or fried chicken or something for ice cream and having an enjoyable meal that is, you know, a piece of fish with some herbs on it or something like that.
That tastes good, but is a more simple unrefined flavor rather than having all these highly palatable accoutrements. Does that make sense? Yeah, that does make it OK. I'll try to keep that in mind this time. I'm picking your restaurants. All right. Well, we really should wrap up at this point, unfortunately, but there's a lot more detail in the hungry brain. So we'll put a link to that on the website. And before I let you go, Stephane, do you want to give the Russian speaking pick of the episode?
It's for this episode. I'd love you to suggest a book or some other resource. That's like if you had to pick one additional book to recommend to people to flesh out their understanding of this topic that you didn't cover isn't in your book, what would that be? I think Michael Moss's book, Salt, Sugar Fat is is a really nice one, and I think so my book is a lot about the science and especially the neuroscience of overeating and eating behavior.
But I think what Michael Moss does is he really fleshes out the kind of the changes that occurred in the food industry and our food culture, that kind of where some of the triggers of this modern relationship that we have with food that's driving us to overeat. So I think I think that's a really nice compliment to add to my book. And it's I mean, even independent of my book is something that I learned a lot from.
Great. Well, we'll link to that on the podcast website as well. Stefan, thank you so much for joining us and rationally speaking.
My pleasure. This concludes another episode of Wrasslin Speaking. Join us next time for more explorations on the borderlands between reason and nonsense.