Dr Rupy: Regardless of us sitting here and having this really civilised conversation and an enjoyable conversation about about calories, this is we are still a minority in in in where we are now. And I think denying that is not going to help. And so you need to continue speaking, I need to continue speaking and we need to continue talking about the importance of food in and of itself rather than anything else and the quality of food and eating eating eating food that is good for us and good for the soul. Welcome to the Doctor's Kitchen podcast. The show about food, lifestyle, medicine and how to improve your health today. I'm Dr Rupy, your host. I'm a medical doctor, I study nutrition and I'm a firm believer in the power of food and lifestyle as medicine. Join me and my expert guests where we discuss the multiple determinants of what allows you to lead your best life. Do you calorie count? Well, you are not alone if you do. It's a multi-billion dollar industry for weight loss, nutrition labelling and of course mandated on food packaging in most countries. Calorie counts are really hard to miss. But how accurate are they? Giles Yeo is on the podcast today. He's a geneticist with over 20 years experience dedicated to researching obesity and the brain control of food intake. He obtained his PhD from the University of Cambridge and assisted the pioneering research that uncovered key pathways in how the brain controls food intake. His current research focuses on understanding how these pathways differ from person to person and the influence of genetics and our relationship with food and eating habits. And he also moonlights as a science presenter for the BBC and you will no doubt recognise him from a string of programmes. Now today's show is all about calorie counting and why calories don't count. It's a very provocative title and it's the title of his latest book, Why Calories Don't Count. Now, I just want to preface this. This isn't a show demonising calorie counting in itself. I think calorie counting for certain people has been beneficial and there's no doubt a calorie deficit will induce weight loss in the short term. But if you've listened to the other obesity related episodes, you'll know that short term weight loss really isn't the goal because that as a long term strategy is not effective. And when we're thinking about food, we should really be thinking about the health impacts rather than the symptom of reducing food energy intake as a means to creating weight loss. So today, what we're going to be talking about is the inaccuracy of calorie measurement, our lack of understanding about the composition of food itself, the impact of individual differences, and this is where Giles's research really comes to play here, as well as the other determinants of weight control. We also have a lovely chat about the differences in calorie calculations and how we got here and how the current method of calculating calories that you'll find on cereal boxes or candy bars or whatever, are based on measurements that haven't really changed in about 100 years, which is mind boggling. We also talk a bit about how we expend energy and how that really isn't taken into account. So things like basal metabolic rate, physical activity and dietary thermogenesis. And we do discuss and explain what those terms are as well. He also has a fantastic eight part podcast series called Dr Giles Yeo Chews the Fat and it's available to listen online wherever you get podcasts. And you can find the show notes for today's show plus sign up to the Eat Read Listen newsletter at thedoctorskitchen.com. I think you're going to find this episode fascinating. Giles is a brilliant communicator and at the start we just bond over American football. I'll let you listen to that, but if you want to get straight to the meaty part of the podcast, just forward the first 10 minutes. Onto the pod. My first question actually was going to be about whether you're, in the nicest way possible, whether you ever get bored of being asked about calories all the time. Do you ever find yourself like, ah, can't we just move on to something else or something, you know, a lot a lot wider or, do you know what I mean?
Giles Yeo: Do I? I mean, I I hope we all get bored with it soon to be fair. I I don't because I think there is so we do worship the calorie, don't we? And I think as a society and this is the the the thing that's weird. So because so because there's so many things wrong, well, not wrong with it, because as long as you use it correctly, but so many misunderstandings about it, I relish the opportunity, and it's a terrible thing to say, in in in order to correct some of the misconceptions. I will be bored at some point, not yet.
Dr Rupy: Okay, fine, fine. Because like, I mean, I get asked about it quite a bit. And well, I mean, I get asked the same questions over and over again, which for for a lot of people is the first time they've heard someone talk about it in, you know, a way that makes sense to them, in a way that's like easy and it's not, you know, restrictive and rigid and whatever. But for me, it's like, I just wish there was a way, like a platform where everyone could just be educated on it and everyone have the the like similar opinions. So there's not this miscommunication. I think that's what the book does very well because you're going through different diets, you go through the pros and cons. There's a ton of humour into that. But before we go into the book, I want to talk a bit about you and where you grew up because I learned a few things and I'm going to tell you a few things about me as well and I think we're going to have a a bit of a bonding experience at the start here.
Giles Yeo: Yo. My brother from another mother. Yeah, let's do this.
Dr Rupy: So tell me, where where did you grow up?
Giles Yeo: So I, this is a complicated story to to to some degree. So my, I popped out actually, so to speak, in in in London because my dad is a, my dad is a medic, retired medic, but he was pinging around. He did his registrar training in endocrinology at King's College London in the early 70s, which is when I was born. And that's why, so so, you know, my mum was and so that's where I came out. But then we then moved back. So I, then he went up to Newcastle. So I spent five years in Newcastle. And so there's this small Chinese boy from Singapore, now with a full full on Geordie accent because I didn't know how to speak. And then we moved back to Singapore. So I was then in Singapore for a few years until I pinged around the world for a bit. I pinged to Boston, back to Singapore, and then we finally emigrated to San Francisco, which is where I did high school and I did my university. And it was then after that that I came to Cambridge to do my PhD and stayed here. So that broadly speaking. So in terms of bringing up, my culture is probably Singaporean Chinese for my early life. And then suddenly this huge cultural change into going to California, to San Francisco. And then from high school and university, which is a very formative moment part of your life, obviously, that that was American. So it was Chinese Singaporean first and probably where a lot of my food culture was embedded, okay? And then my culture culture, the way I think and stuff was probably done in California. So that broadly speaking is me.
Dr Rupy: That's, that's fascinating. I mean, like, when you read the book, your humour comes across very British, if I'm honest. It's it comes through in every single page and you know, the memes that you talk about and stuff. But the the stuff about you growing up in San Francisco was super interesting because you said at the start, you're a big NFL fan. Is that still the case?
Giles Yeo: I am. 49ers, go. They're not doing very well this year.
Dr Rupy: No. So I'm going to tell you something. So I'm a massive NFL fan.
Giles Yeo: Are you?
Dr Rupy: Yeah, so I got into it when I was at school with my best friend who now lives in Chicago. It was his dream to always move to America and he ended up doing that in his 20s. He got me into NFL in a big way. He was a big Minnesota Vikings fan. Okay. And I went to Harvard just to go visit the campus with my parents. So we did this whole trip. We went to like Cape Cod and some other parts in Boston and stuff. And I picked up a shirt and it was a 24 Ty Law. He was the the cornerback for the Patriots in the year that they won that. So I picked up the shirt and that year, the whole issue with Bledsoe and Tom Brady, Tom Brady came in, the fourth pick, you know, from the draft. People who people have no idea about NFL are like completely confused right now. But anyway, he was like, you know, the bottom of the rank, he came in, won the Super Bowl, became, you know, the poster child for NFL across the world, like the the Michael Jordan of the NFL world essentially.
Giles Yeo: The goat, as they call it. Yes.
Dr Rupy: The goat of American football. And I've been hooked on on the Patriots ever since. But interesting thing, I got really into it when I was at medical school. And John Taddy that we were talking about earlier, he will attest to this. I would go to the sports cafe every Sunday to watch the games on my own because no one else would go with me because no one understood American football. Yeah, I was there on my own. And I played fantasy football and I won the Sky Sports fantasy football league in the UK in 2024, 2004. So I got, yeah, so I got tickets to go to the Super Bowl when the Patriots played the Eagles in Jack. I know, I know. For those who are listening, I like to listen, listen, we're here to talk about calories, but no, let's move. Let's go, let's change subjects now. This is what? Yeah, yeah. So this, I mean, no one, no one knows this. I haven't spoken about this for for years. And no one would be able to appreciate this. This is like essentially being given tickets to go to the World Cup watching your favourite team, like whether that be Brazil or something in Brazil.
Giles Yeo: I mean, tickets cost ridiculous sums of money. Like, you know, all the fancy people go, you know, and and and and and it's like 15 grand or something or 10 grand for tickets. And you see Beyonce at halftime and it's just a crazy event.
Dr Rupy: Yeah, it was a crazy, crazy event. And you know, so I won the the thing in Sky Sports. So I played every single week and I remember the the league table was announced live on Sky Sports. And I remember watching it with my baby sister and my dad. My dad had no idea what was going on, jumping up and down. And yeah, no, the Sky Sports team sent me out there. They gave me accommodation. We went to the tailgate party. It was like the best time of my life. That like, honestly, and I was like second year medical school or something like that. So like, you know, it was it was brilliant. It was so fun. I thought you'd appreciate this.
Giles Yeo: I'm speechless. I I I'm speechless. We we we could end the end the conversation now. See you later. Thanks for having me.
Dr Rupy: No, see you there. Thanks. Okay, NFL aside. Let's let's talk about the book because the the book has got quite a provocative title, right? And I know right at the start of the book, you you you tell people to hold their horses and not at you. But despite that health warning, I reckon you've been ated by a number of people since this book coming out, right? So so so why don't we get to the crux of of the book? I know it's got a provocative title, but what what what would you say is the overarching theme of why calories don't count?
Giles Yeo: Oh, I think there is if I only had one sentence to say, it's very, very simple. We eat food and we don't eat calories. And I think that's the absolute critical basis of it. People think about calories. The calories are the units of energy that once you extract it, and and they are equal once they're in you as a little poof of energy, okay? But that's not what we eat. We eat food and we can eat good food, bad food, healthy food, whatever it is. And then our body then works to to to take apart the food, digest and extract the calories. And so we need to concentrate on the food rather than the calories because the calories are just an output of the food. And so what we eat influences how many calories we actually get out of the food. That in essence is why calories don't actually count. They count, just let me just before we count. Clearly 200 calories of chips is twice the portion of 100 calories of chips. But so is 200 grams of chips twice the portion of 100 grams of chips. And no one is trying to compare 200 grams of chips to 200 grams of carrots. So it's not quite that extreme, but the analogy is there. That's why calories, I think, don't count.
Dr Rupy: Okay, fine. So we'll we'll get to the nuance of the the calories and how they might be differently absorbed and differently utilised depending on the person consuming them. But let's go down, seeing as you love talking about calories, as we've established at the start, and you're not bored of it yet. Let's let's let's go down memory. I wanted to I wanted to qualify actually because I didn't want to ask you the same kind of questions and you're like, okay, fine. But let's let's let's go into the history of of calories and and where it came from because you do a beautiful job of going through, you know, how this came about, the the progression of the science since the the pre-French Revolution, I think it was with Antoine, I'm probably going to butcher this name, but Antoine Lavoisier.
Giles Yeo: Beautiful.
Dr Rupy: Oh, beautiful. I know. I wish I could speak French actually. It's just like a love, it's such a mellifluous sounding language. But anyway, Antoine Lavoisier and and and how we how we got here to this point.
Giles Yeo: So, I mean, it is very, it is old. It is very, very old. And it's when people were trying to to understand almost transfer of matter from one to the other. You know, what happens when you burn wood? Where does the wood disappear to? How come it disappear? And this was the the concept that that Lavoisier was actually was actually thinking about. And and so he began to realise that when you actually transfer that matter doesn't disappear. He he in effect was was the first person, I don't want to say the only person or I don't know if even he was the first person, but he certainly put into practice and enunciated the concept that when that matter doesn't just disappear out into into nowhere, but it's just transferred. It may be transferred into heat, it may be transferred into other chemicals and other molecules. It it's transferred from solid to to to gas, whatever it is. And he got this concept. And he also came up with, so he was an amazing character actually, before he was guillotined in in in the French Revolution. So he was a bit of a privileged person. But he, for example, almost described the concept of the element and he described oxygen and he described, you know, hydrogen. He didn't call it exactly those things, but he actually identified that earth, wind and fire was is not just earth, wind and fire, but it's actually there are elements involved. The point is, because he understood this concept of matter being transformed, he was the one that brought up the concept that you needed oxygen to burn something. This is this is pretty much it. And when you burn something, carbon, you know, wood or anything like that, you then produce this this concept of carbon dioxide. And so it was this concept that he was he was actually thinking about. And then, because when you burn something and then heat came off and energy came off, he then began to, he never used the term calorie, okay? But he did begin to give the concept of heat being given off when stuff was happening, okay? Including, including, he finally worked out and and and went to the situation that burning a piece of wood meant oxygen and giving off CO2. And he then equated that to when we ate that the food was then being burnt, oxidized, okay? And CO2 given off. And he equated the two things together that they were similar processes, which which they are in many ways. And that is in very many ways the birth of the calorie because he then realised that, well, wait a minute, with heat is given off when you burn a piece of wood. And if we eat a piece of meat or or vegetables or what have you, that we must be giving off, that it must contain these calories, which he didn't name, these calories as well. And that was really the birth of the concept that when we actually ate food and burnt it, it was like burning, it was like burning a piece of of of wood or burning a piece of fuel. And that's what we say, right? So we now we say, well, how much food did we eat? How much energy do you burn? And and we still use the term. And that energy you burn term actually originally came from Antoine Lavoisier.
Dr Rupy: That's that's fascinating. So so this this whole concept of transferring energy being applied to human beings, like we're little furnaces, for example. And that transfer energy not being, I mean, it has to go somewhere. So that that was introduced by Antoine. And then thereafter, the science sort of progressed even further. So he he didn't come up with the calorie. I remember you saying that in the book as well. Where did the the the calorie itself, where did that come from?
Giles Yeo: So actually, where that then came from, from the Germans, the Germans. And and it came from the Germans and German agricultural actually, because what then happened was, it then quickly went into, okay, there was a middle ground in which it involved some French people, more French people, in which where was the calorie, where did the whole concept of the calorie came from? And it was, it became a measure of heat, okay? And so people began to understand and begin to nail down how much what a calorie actually actually meant. And as you know, we now know that a calorie is a unit of energy that raises water, the temperature of water a certain a certain amount. And so when that then came to be, then people started thinking about, well, how do we measure them? And then a, then this is when we went back into into the French munitions manufacturer, okay, of all the things in the world. And they came up with the concept of the bomb calorimeter. Yeah. Okay, where we could then, in effect, you you sort of, I mean, they were using it to measure the energy output of a bomb. Like seriously, literally. But and and and they invented it. But then people then, and these were then the German farmers, agricultural industry, begin to utilise it to measure how much energy there was in food, rather than in bombs, in food. Why agriculture? In particular, domestic, you know, cattle and what have you, because farmers really care how much do they feed their animals, therefore, how much milk and meat you actually get out the other side. And so they were the first people to really be concerned about exactly what they were feeding their animals and therefore exactly what you output it. And they begin to use this bomb calorimeter to measure the total amount of energy of energy in food. So so so you went from the whole concept, this this rather ephemeral, ethereal concept of heat being produced, and then slowly working off of into a way of measuring it, and then finally moving back into food again because of agriculture. And now, because of agriculture, we now have this concept of calories being being the energy content of of of food.
Dr Rupy: Yeah. So sort of born out of the the commercial side of agriculture. So you're trying to transfer energy into your livestock so you can plump them up and you can figure out how much
Giles Yeo: in as in as efficient a way as possible. So for every penny or pound, whatever, whatever money it was at the time that that was being put in, you were trying to be as efficient, it was a based out of need. How can I be as efficient as possible? What can I feed my animals, you know, to get the best meat and the best milk for the least possible money that I can put in, pretty much.
Dr Rupy: Got you. Okay. And was was that the time where we figured out the differences between the energy in the different macronutrients, so fats and carbs and protein? Or was that pre that was was that preceded?
Giles Yeo: This, so this was before, because then what happened was we have to introduce another person. And this was a guy, so now we are at, just chronologically for those of you who are, we're now probably in the late 1800s, okay? So we're about 1880 or so. And 1880, it was actually before that, 1870s, a guy named Wilbur Olan Atwater, okay, came came to be. So he was a professor of chemistry at Wesleyan University in Connecticut. And he was interested in the concept of the calorie. And so he visited, he visited one of these agricultural stations. They had these agricultural stations in in Germany where they were doing the science on a sabbatical, pretty much, okay? And so he went and he he learned a couple of things. First of all, he understood the concept now of bomb calorimetry. He understood what they were trying to what they were trying to do. But these were these were the agricultural industry. He then went back to Connecticut and set up these agricultural stations as a concept in the United States. But his interest then was not what happened when the cow ate, whatever it is you you fed the cow, but hang on a second, if we could do that for animals, surely we should be thinking about doing that for humans. And so then Atwater between the years of 1880 and 1900, and I want everybody listening to this to consider this before you complain about your job again, because what Atwater then did between 1880 and 18, so so Atwater understood what I call the sweet corn phenomenon. When you we eat the sweet corn, and you look, you look at the loo the next day, you clearly haven't absorbed all the sweet corn. We understand this phenomenon. He understood this phenomenon. And so he decided, well, you know, how much, how much of the of the energy are we absorbing? So he, in over 20 years, put lots of food into a bomb calorimeter to burn food and measure how much temperature came off. Lots of food, all kinds of food, all the foods you can think of. But critically, he then fed these foods to human beings and then burnt their poop, all right? Like literally, for 20 years, this is what he did. So now he understood how much energy went in the top end and how much energy went out the back end. And because he understood this, we now we now appreciate, he now appreciated, pardon me, how much energy we absorbed, okay? And so based on that, he then came up with his famous Atwater factors. And and these Atwater factors we still use today. And this are the nine calories for every gram of fat, four calories for every gram of carb, and four calories for every gram of protein. And he did this in effect over 20 years because of this burning and feeding and burning. And he published it 1901, 1902. And so all of the calorie counts pretty much everywhere that we see are more than 120 years old based on Atwater's burning experiments.
Dr Rupy: Wow. Okay. So with these burning experiments, just just to hold on to that that image for for just a second here. So he would burn it in a in a controlled environment, I I guess, and collect the gases to estimate the energy. Is that is that what he would do?
Giles Yeo: No, no, no. So a bomb calorimeter is a sealed container where you put desiccated, dried food into or or poop. Okay, in into the container. And why dried? Because water to at least to a human being does not have any calorie content. Now, if we are a nuclear power reactor, then water has, then we can break apart the, but we're not, okay? So so water has no calorie content to us. So if you dry off the water, just evaporate off the water, and you then have the dried food that is there or poop, and then you put it into a sealed container that is pressurized with pure oxygen. And the reason why you do that is so that everything burns. And then you, in effect, you put a spark of electricity. This, by the way, is still the technology we use today. It's just the machine just looks a bit better. And you spark and burn it. So but around this sealed container, this sealed pressurized container, is a water jacket of known volume, X litres of water. And so you burn the food and literally you have a thermometer in the water jacket and you measure what the temperature, and a calorie, a heat calorie, a small C calorie, is the amount of energy it takes to raise 1 ml of water 1 degree Celsius at sea level. A food calorie, which is 1,000 little calories, is 1 kilocalorie, is the amount of energy it takes to raise 1 litre of water 1 degree Celsius at sea level. And so that's how you measure it. You burn food, you have a known volume of water, you have a thermometer in, and you just measure what the temperature of the water raised, and that is how you calculate the total number of calories in a food.
Dr Rupy: Right. Or poop.
Giles Yeo: Or poop. Yeah.
Dr Rupy: And we'll we'll put kilojoules to one side for now because I think I think you explained that really well in terms of the differences in the book. But just to reiterate the point, so these calorie measurements that were calculated by Atwater in around 1900, 1902, 1903, have not changed in over 100 years. And this is still how calorie counting books and calorie counting apps all all work. Is that is that fair to say?
Giles Yeo: Now, that's correct. Now, there is a little bit of wobble. So in other words, you're now you're going to listen to this and you're going to go to your cupboard and and begin to calculate. You'll find a little bit of wobble. And the wobble comes primarily from the way people calculate how much protein there is in a specific item of food. So because of that wobble, there's a little bit of other things, but there is a little bit of wobble, but pretty much it's based on 449, right? For those factors.
Dr Rupy: Yeah. And and protein is slightly different because there's different energy consumption to break down certain types of protein, right? Regarding where it comes from.
Giles Yeo: That happens later. So so so so the problem is what they actually have calculated, this is entirely based on the on on the burning experience, burning experiment. The wobble comes from the fact that so fat and if I might just to just to be boring slightly and nerdy for a second, fat and carbohydrates are are made exclusively of carbon, hydrogen and oxygen, exclusively. Okay, that's all in different configurations. The the thing about protein that will be relevant in the metabolism error element of it as well, but this is just the digestion element, is that it also contains nitrogen. And nitrogen is very, it needs to be dealt with. And and when we are actually dealing with protein, if we don't use it and we have to and we have to move protein and transfer it and make it become fat, for example, you need to get rid of the nitrogen. And so the nitrogen then comes out as we wee it out, all right, pretty much. And when it comes out, but but so dealing, the way that most, the way that everybody pretty much actually calculates how much protein there is in a food is by estimating how much nitrogen there is in a food and how much it actually comes out the other side. So this is the complexity, but all proteins, there are 20 amino acids that make proteins, do not contain the same amount of nitrogen. And this is part this is part of the problem and the complexity of it, which is why there's this wobble. So people never, you you can empirically determine how much protein there is in a food, but that takes a lot of effort. So people estimate how much protein there is in a food. And so it's a little bit when when when you're when you're there.
Dr Rupy: When you're there. Okay, fine. So so we've established the the history of the the concept of energy transfer, the measurement of said energy transfer using calorie, how we measure the calories in food. Um, how the fact that these calculations have largely been unchanged for a long period of time. Where where are before we go into the issues with the calories themselves, why don't we talk a bit about how we expend said energy when it's when we consume it. So, uh, you mentioned three areas in in the book. You have your your basal metabolic rate, your obviously your physical activity and your dietary thermogenesis. And I think then we can get into the conversation about the the nuance discussion around energy transfer and why this isn't necessarily hold true considering we eat food rather than a a jumbled up mix of calories and various flavours.
Giles Yeo: So what we do with energy, we do, I mean, you've already said it very well actually. So energy, so you've obviously we eat food and we have we burn the food. And and we burn the food primarily for three in three different ways, okay? And this is it adds up to 100%, but obviously these things move. And the first and greatest amount is your basal metabolic rate. And this is what people generally in in common vernacular we call your metabolism. My metabolism is fast, it's slow. And this takes around 70%, pretty much 70% of the energy that we actually consume is spent on this. And your basal metabolic rate is everything that keeps you alive. Your brain working, your heart beating, um um breathing, all of the things that we have to do even if we're lying down and doing nothing, okay? And that actually takes 70% of the of the energy you eat to do that. The other 30%, you can in some way do something about, okay? So your your basal metabolic rate, interestingly, this 70%, we have almost zero effect on, okay? Our body size and how much we exercise and how much muscle we have influences this. So we have we can do a little bit about it, but actually the rate is the rate that that that it is. The other 30%, however, comes from two elements. It comes from physical activity, and this we all understand what it is, all right? The more you exercise, you you know, you can change the amount that that you actually burn from there. And crucially, what we call diet induced thermogenesis. And thermogenesis means heat production. And when we eat, it takes, when we eat, it takes energy to, it takes dough to make dough, okay? And so it takes energy to make energy. And this energy is when we eat, your body then gets into into a situation that we needs to metabolise the food and that is diet induced thermogenesis. And so that is heat that that actually comes off as well. In terms of percentages, physical activity we're probably talking around of the 30% that's left, around 20%, okay, of your energy, roughly speaking, clearly that can shift if you're running the London marathon, for example. Um but then the other 10% is probably diet induced thermogenesis as well. And thermogenesis in general, actually. So in other words, if you are non-shivering thermogenesis, which means that you're obviously you're shivering, this is this is still physical activity when you're doing. But then if you are just producing heat to try and keep yourself warm, that's part of thermogenesis, heat generation as well. So diet and thermogenesis is about 10%.
Dr Rupy: This is a slight uh uh side by here, but people who are jumping into cold baths uh for varying amounts of time, are they activating uh a certain area that is going to increase their uh their calorie uh um their calorie expense, their calorie consumption?
Giles Yeo: This is the theory. I don't know how, I don't know if a single cold jump is going to do this. There is a bit of our, we call it brown fat, okay, in in our body. It's not actually fat. So fat is energy storage. Um brown fat is called brown because it's got so much mitochondria, which is our energy, which is our energy supply, powerhouses in our in our body. It produce, well, it produces energy, but in brown adipose tissue, brown fat, pardon me, same thing. But brown fat, it's not linked to producing um um energy for us, it's linked to just producing heat to actually keep us warmer. And so the smaller mammals, mice and what have you, will have a larger percentage of brown fat compared to normal fat. Um babies will have a larger percentage of brown fat compared to to us who are in central heating and wear jumpers. But then if you, however, are um say an Inuit in the past who actually live in an igloo, you you you're out in the middle of nowhere, well then they would have a lot more brown fat as well to keep them warm. So the whole concept of jumping into a cold, you you you know, icy icy water is to try and upregulate your brown fat, you know, there are other things as well as far as I understand, but this is part of it to try and increase your energy expenditure.
Dr Rupy: Yeah, yeah. I've only jumped in a cold bath a couple of times. Um and it's it's invigorating uh afterwards.
Giles Yeo: That's a good word for it.
Dr Rupy: Yeah, it's a it's a good word. And you you jump out and uh you feel amazing for about 10, 15 minutes. But every time I've done it, I get a cold like three days later. And I can't tell why. I don't know whether it's because like my stress response just goes through the roof and then I
Giles Yeo: And then your immune system then plummets because of because of the whole thing. Yeah.
Dr Rupy: Yeah, yeah. I think it might be that from from that like high degree of stress and then I deplete my reserves for one of a better word and then I I get a cold a few days later. So for me it's never really worked and I I just instead go for a run without my jumper every now and then and you know, I mean creating as much heat anyway. So uh yeah, I don't know if you've ever jumped in a in a cold pond yet.
Giles Yeo: I no. Well, I tried once. It was so unpleasant um that I said, do you know what? If the whole concept is to try and and increase, I like you, what I do is my my favourite exercise is is is cycling. Is if it's my thing is if I start cycling and I'm already warm, then I'm wearing too much clothes. And so I always and my wife thinks I'm crazy. But so when I start cycling, I go out where I'm okay, I'm not freezing cold. Clearly, I'm not I'm not a masochist. But I need to be slightly chilly, okay? It needs to be slightly uncomfortable almost when you start because by the time you're in, say 15, 20 minutes in and your and your engine is up and running, I'm fully comfortable. And so then is a situation where I'm not cold, I'm now producing heat and so that is my my my ethos. My wife thinks I'm mad. She goes on a big jumper.
Dr Rupy: Yeah, actually my my fiance is the same. She always looks at me when I'm about to do a run outside and I'm just like, I've just got a hat on, a t-shirt, shorts or whatever. I'm just about to go running. She's like, you are crazy. Like, what are you doing? Just put a jumper on.
Giles Yeo: What are you doing? It's too cold.
Dr Rupy: I said you heat up pretty quickly.
Giles Yeo: Yeah, you do. Yeah.
Dr Rupy: I really enjoyed the story actually about you uh uh hill cycling uh in your lycra. I I hadn't come across the was it mammo? Middle-aged men in lycra.
Giles Yeo: Mammo, M A M I L. Middle-aged men in lycra. That's me. That that that that's me.
Dr Rupy: Does Jane cycle as well?
Giles Yeo: Not in lycra. And she's got an e-bike. So listen, listen, domestic bliss is hard won. I just want to point out to you. And so um um with with with her with her e-bike, me you you you know, you know, in this masochistic thing, we you know, maintain domestic bliss. So I can work myself stupid and she can have a have a good time and and our marriage stays in bliss.
Dr Rupy: That's fantastic. That is fantastic. I have to admit there was a part of the book where I remember getting the chemistry lesson from you and it just brought back loads of memories from second year of medical school.
Giles Yeo: I'm sorry.
Dr Rupy: I know, I know. But I I did feel uh vindicated when you were talking in about how you probably forgot a lot of this stuff as soon as you left the examination hall because that's like that was literally like my experience as well. Like I would I would revise so much. I'll learn all these different pathways and then an hour after the exam, it would just like just filter out of my sponge brain that couldn't hold on to the uh the juicy liquid of knowledge.
Giles Yeo: What a waste of but what a waste of glucose. What a waste of ATP. But anyway, that's
Dr Rupy: I know. But the the I it reminded me about how cells contain hundreds if not thousands of mitochondria, which I thought was absolutely fascinating. I I I didn't actually grasp the magnitude of the mitochondrial density that you find in cells. I mean, that that is the basis of of how we we break down energy or we create energy, right?
Giles Yeo: That's correct. That's correct. And and people think it's just one or two mitochondria. No, it's actually depending on what you're talking about, particularly in your muscles, we're actually talking hundreds, thousands of copies of of of mitochondria.
Dr Rupy: Yeah, yeah. And so, uh you mentioned uh basal metabolic rate uh here being the the largest uh way in which we expend calories. So let's talk about that relationship to size because I think people um I mean, everyone's everyone's heard that term, I've got a slow metabolism or you know, I'm big bone or whatever. Um but what what is the relationship to size and and your metabolic, your basal metabolic rate in particular?
Giles Yeo: So you're absolutely right. A lot of how many times have you heard it, right? Oh, no, I am larger because I have a slower metabolism or or what have you or I'm smaller, so I have a higher metabolic rate. And this is just not true. So the biggest, the biggest determination of your basal metabolic rate is your size. I mean, specifically, it's actually depending on what part of your body you're talking about. If you have more muscle, you have a higher basal metabolic rate. If you have the fat is less metabolically active than muscle, but your total body part of weight. So the larger you are, the higher your metabolic rate. The analogy will be that while if you look at a mini mini, okay, like an old school mini Cooper and it zips around and you think, oh, look at it, it's it's it's pinging around. Whereas if you look at a big SUV, it kind of it kind of moves about what what looks like slowly. But at the end of the day, the big SUV will always use more um um fuel than the small tiny car. And the same is true for for for body sizes for for us. So the bigger we are, the more fuel we use, even though we appear to be slow and lumbery and whereas this skinny wiry person, you know, looks like, you know, really energetic, it'll always use less energy than than than the larger person.
Dr Rupy: Okay. So we we have this would you would you say it's like a non non-linear relationship to size, our basal metabolic rate?
Giles Yeo: It is non-linear. So when when and when we mean non-linear, we mean that if you are twice the weight of someone, you don't have a metabolic rate that's twice as fast as someone else. And how you calculate that is actually relatively complex and I go into it, but it's it's not linear. So so so it's not, is it geometric? I don't know. I forgot my maths. I I don't know what what exactly it is, but it's not it's related. It's definitely directly related, but it's not it's not like twice the size, twice the twice the metabolic rate.
Dr Rupy: Yeah. It's not proportional to the size. So if you if you're twice the size.
Giles Yeo: That's right. It's proportional to the size, but it's not it's not twice the size, twice the twice the metabolic rate.
Dr Rupy: Yeah. Great. Okay, great. So we've established all these uh facts about calories, how we burn calories. Let's talk about um a bit about why the calorie theory just doesn't hold up uh today. So what what are the other nuances within food itself that uh will differentiate will will um what's the word I'm looking for? will explain why the calorie count on the pack of food doesn't correspond to the energy that you consume or or or utilise in that way.
Giles Yeo: Okay. So there are two stages to the way uh there are two stages to us getting the calories from the food because we eat food, not calories. Um the first is digestion and we understand what digestion is, mechanical digestion is where we chew and the washing machine sound that our stomach makes peristalsis. Um and then the long huge chemical reaction, which is largely what digestion is, which then breaks down the macronutrients into sugars, fatty acids and amino acids, which are the broken down portion of protein. Now, once this happens, it's absorbed into our blood, okay? That's the digestion element. Atwater's burning experiment took into account how much of the sugar, fat and protein we finally absorb into our blood. So he he he got that done. The second part, however, is that because once we get sugar, fat and carbs, sorry, sugar, fat and protein, amino acids into our blood, that's not the end of the story. That is not our fuel. Sorry, that's not our energy. It continues to be fuel. So this sugar and fat is then transported to our organs that matter or cells that matter and are then metabolised into energy, okay? So that that that is the critic, that's the crucial thing. And it's this stage that takes a lot of energy that Atwater didn't, couldn't take into account. And this differs whether or not we're talking about protein, whether or not we're talking about fat, or whether or not we're talking about sugar or or or carbs. And so we know, for example, that a calorie of protein makes you feel fuller than a calorie of fat, than a calorie of carb in that order. And a large part of that is because of the amount of energy it takes our body to metabolise to metabolise each of these individual macronutrients. So one, just to put some numbers on it, to put some some flesh on the bones. So for every 100 calories of protein that you will eat and and and absorb, we our body is only ever able to use 70 calories, 70. So 30% of the protein calories we eat is used to sort out protein. In large part because they have to get rid of the nitrogen, okay? So this is this is part of the issue. This is why it takes so much energy. So if you actually look at the calorie counts everywhere, the protein calories are 30% wrong. They're already out by by 30% before we even begin to discuss anything else. So that's the most extreme, I think of the differences. How about carbs? Well, it depends if we're talking about the powdered white stuff, which actually is very, very calorically available, okay? It takes very little energy. 97% available. So for every 100 calories you eat, you need three calories to deal with the sugar. So 97%. Whereas if you have whole meal bread, you stuff with fibre in it, then it's about 10, it takes 10% of energy. So for every 100 calories, you need 10 calories to deal with a slice of whole meal bread. Fat is very efficient. And so Atwater was correct with his calculations for fat. Fat is fat and it's nearly 100% available when you eat it. It takes nearly, it takes next to no energy to deal to deal with fat. And so there we go. That those are and and those differences in numbers come from the metabolism because Atwater has already taken care of it in the digestion element of it. So in total, I would probably say the calorie counts on all the foods are probably out by about 10, 15% depending on how much protein and fibre there is in the food.
Dr Rupy: Okay, fine. So but that's not the end of the story, is it? Because otherwise your book would be called why calories don't count parentheses as much. So so so you there's like the the the uh net metabolizable energy calculation there is. But then also there's the actual food. So uh when I'm when I was imagining a food when you were making that description, I thought of like um uh like a nut, let's say an almond. An almond has got a lot of fat, it's got protein, it's got carbohydrate, it's got it's got the mixture as most foods do in varying proportions. So when we look at uh the almond, how does that calorie uh adjustment make how do we make that calorie adjustment in an almond considering the different proportions of macronutrients?
Giles Yeo: Oh, okay. So that is not an easy question to answer. And I think I think in and I think in many ways, we need to do that for each food individually. So it will for now still always be predictions because it is because obviously, we can obviously take the almond apart and say what percentage fat, protein, carb is in there and sort of work out what the calorie counts are. But that doesn't tell you how they interact together. And because how they interact together really, really influences. I I'll give you a better example might actually be an orange, okay? So where for if because you can obviously everyone knows what an orange is and we know that when we squeeze an orange, we get orange juice, okay? So it's exactly the same food except when you squeeze the orange juice, you get this pulp that's left, which we think well we can't digest anyway and we drink the orange orange juice. The difference there is enormous, okay? It's exactly the same amount of calories we can absorb in the orange juice because it's mostly in the sugar and in the orange. But just by the fact of us eating the orange, a number of other things happen, which means that the total calorie, the the sugar calories in in the orange are dealt with completely differently. We first of all, we're eating as opposed to just drinking the sugar, all right, which is in orange juice, which incidentally has as much sugar as there is in Coca-Cola or or any other soda, okay? And and natural sugar is not better than Coca-Cola sugar. It just isn't. So just by the fact that you have a whole orange there that you're eating and you're dealing with the fibre and you're eating it and your digestion system is worked on it, the way that the sugar is released, first of all, takes a longer time rather than just just just going in and spiking in your in your blood. Um but then the presence of the fibre, the way that our intestines work, um helping the microbiome as it as it, you know, the bugs in our gut as it goes down, um helping us be regular. So there's this whole, you know, other holistic element of it of eating the food that comes into play beyond purely the calorie. Because if it's purely the calorie, then drinking the orange juice and eating the orange will have exactly the same effect. And that's not the case. You feel fuller with an orange, you know, and everything is going to be better. Whereas with the orange juice, I'm not, okay, before people in the orange juice community, you know, start start throwing stones at me, I'm not saying orange juice is bad for you, okay? I'm just saying that there is a substantive difference even though it's the same source food between eating the orange and drinking the juice. So I think that is what we need to really take into account beyond counting the calories in each of the individual macronutrients.
Dr Rupy: Yeah, yeah. So within the um foods, there are inaccuracies in how we calculate the calories. Within uh the same foods, there are different preparations that we can go into in a second as well, that will determine the amount of energy that we absorb. And then that's before we actually get into the individual differences of the person consuming said food as well. Correct. Their current weight, uh their proportion of uh visceral fat, um their genetics, something that I'm sure you can speak about.
Giles Yeo: How how active they are, you know, all all of the things, all of the things that you have to put in.
Dr Rupy: And the state of the microbiota as well. Um which is a whole other field. And and I know I I'm going to ask you to sort of postulate here because there's a lot of unknowns, I think, in terms of how we can assess people's microbiota and how that actually impacts um the the the extraction of energy from food as well. Um but what what do we what can we tell about um someone's microbiota state today and how that impacts the energy uh consumption from the same food. So the same bowl of cereal can can the energy consumption from that be different from person to person based on their microbiota differences?
Giles Yeo: Oh, undoubtedly. So so just just to get some nomenclature, your microbiota is the population of bugs that live in our guts and there are as many bugs that live in our gut as there are cells in our body. So 37 trillion in in in our guts. I think um many people would have heard about this. They heard about prebiotics and probiotics. Um I'll give you my my my um and people always ask me, you know, is micro is the microbiome is a good science? Is it bad science? I think it's relatively new science and I think that's part of the we still are understanding more about it every single day. But what is clear, crystal clear is that we need a healthy microbiome to be healthy, okay? And and what does a healthy microbiome mean? In its most simple terms, okay, as varied as possible. So we want a whole different variety of of of bugs in our in our gut because with variety comes a better ability to deal with food, right? Because obviously, if you need certain types of bugs to help you digest or metabolise certain elements of the food, well then the more the kinds of bugs that you have, then well then the more different types of food you can actually you can actually deal with. The bugs play a role, a big role in our in our health, primarily actually in the immune system because well, the bugs have to interact with our immune system and it actually plays a big role, big role in our our immune system. So that that's what we definitely know. We need a healthy microbiome. We can debate whether or not by changing our microbiome, we can make someone fat or skinny or or smarter, but we need it to be healthy. And the key thing about getting it healthy is to feed it as much fibre, as much different types of fibre as possible. Eat a rainbow, you know, people say eat a rainbow, um um type of thing. And today's modern food environment, sadly, um is lower in fibre than we should be eating by quite a bit. Um and if you actually go to a higher income country such as here in the UK, such as in the United States, we have now, we, not me personally, the the field has now shown that our microbiome on average is far less varied than if you go to a country where they're eating far more fibre. And when they're eating far more fibre, their microbiome are just more varied, um um and healthier in inverted commas. And that's where we are at the moment. We are at a moment where in the UK, we need to increase the variety of our um microbiome, the the the variety of the species of bugs in our microbiome. But we don't need to do this using expensive methods. We don't, okay, of of of eating expensive pre and probiotics. We just need to eat more fibre, maybe more ferments, okay, more more more things like sauerkraut and things as well. But the most critical element of it is fibre, as much as possible.
Dr Rupy: Yeah, yeah. And I love the way that you paint the picture in the in your writing about the current state of the food environment as well. Um I think the Marmot review really brought that into a lot of people's attention as well with regards to food security and how difficult it is to navigate a landscape where you are um bombarded with ultra high processed food. Um that is, you know, a lot cheaper or there's a perception of it being a lot cheaper as well uh compared to whole foods, um depending on, you know, your your time constraints, the education uh level that you have to actually prepare the food from scratch, all these different elements. One thing that really did stand out to me is um how ultra high processed food creates less diet induced thermogenesis. Um I I I don't think I'd fully appreciated that before. Um is there what's the particular reason as to why that might be the case?
Giles Yeo: There are probably a whole lot of other complex reasons, I'm sure as well. But it a big part of that um comes down, okay, so just once again, let's just be clear, processed foods are not necessarily bad for you because cooking is a process, fermentation is a process. So we eat processed foods. Most of our foods we eat are processed in some way. Ultra processed foods is processing of foods that we can't do in our kitchen or or most restaurants, okay? So so so it's the stuff that are pretty much most of the pre-packaged stuff that we buy is going to be ultra processed because it's industrially processed. Now, the and I'm not an ultra processed food Nazi, okay? I'm just I'm not. Let me tell you what the problem with the ultra processed, most ultra processed foods are. The because they're ultra processed, they are stripped of protein and or fibre, depending on what we're talking about, all right? depending on what we're talking about. It's just the way it is. The processing just removes protein and removes fibre. Um and it also removes flavour. So as a result, you have to add back in flavour, which comes from the Holy Trinity of sugar, salt and fat. So ultra processed foods tend to be lower in protein and fibre and therefore calorically very available, which means that our body uses very little energy to get the calories from ultra processed foods compared to a steak, compared to celery. Um and typically higher in salt, sugar and fat. And that is the reason why ultra processed and we eat too much of it. In in this country, UK, we get more than 50% of our calories from of our energy from ultra processed foods. So it does make a big difference when we're talking about ultra processed foods. But primarily, protein and fibre, that's lack thereof. That's what.
Dr Rupy: Yeah, yeah. I think a lot of people like will will rag on the food industry, but um you know, looking at it from a different perspective, they've been responsible for improving the food supply such that everyone has calories. They've made it super palatable. Um they've made it, you know, verging on, I would say, addict. I mean, I I can't keep junk food in my house because I will just continue to eat it. I mean, it's delicious. Don't get me wrong. But like, you know, I have to make a concerted effort to make sure that I've got a good selection of other healthy foods in in the house.
Giles Yeo: Likewise, likewise. I don't, to my mind, if I don't have it in the house, then I won't eat it just without thinking. I mean, I don't mind having it outside and and what have you, but in the house, I try and keep it clear of of of that stuff as well.
Dr Rupy: Yeah, yeah. And I appreciate definitely the the way you describe the um uh the the need for some processing. The way I describe it whenever anyone asks me about processed food is that, you know, all food exists on a spectrum. On one side, you have like raw food here, which ideally you don't want to be eating completely 100% of your diet from. Some degree of processing is normal. Even if it is steaming that tender stem broccoli, that makes it go that beautiful vibrant green colour. You're making a lot of the nutrients a lot more bioavailable. It's a lot more palatable, digestible.
Giles Yeo: Toasting the spices. You know, you have to do that. All all that thing, a little bit of oil in. So these are all processes that make food part of the joy of of of actually eating. Not what we're talking about here.
Dr Rupy: Yeah, yeah, exactly. Yeah. And and on that note, I'm definitely going to be uh cooking some of your uh recipes in the back of the book. The uh is it the the black the black beef brisket, the Chinese black beef brisket? That sounds incredible. Lots of garlic.
Giles Yeo: Lots of garlic.
Dr Rupy: 250 grams of garlic. I had to read that reread that. I couldn't believe it. 250 grams.
Giles Yeo: Try it and try it and report back. You won't taste the garlic. It'll just be so umami and rich and delicious.
Dr Rupy: Okay. Okay. Well, I'm I'm a garlic fiend. I mean, I put garlic in everything. You know, I come from an Indian background. We just shove garlic. Uh the the Holy Trinity for us is garlic, chili, onion. And so everything is forms the basis for that, you know, all our curries, all the different, you know, uh blends up and down the country. It's amazing.
Giles Yeo: For for the Chinese, it's ginger, spring onion and garlic.
Dr Rupy: Ah, there you go. There you go.
Giles Yeo: That's the Holy Trinity. Yes.
Dr Rupy: So looking looking into the future uh for you, I mean, we always see you on our screens on on BBC and obviously you've written a a bunch of books now. What what what are you most excited about um uh in in for the future for your personal research, but also things that you might be writing about next?
Giles Yeo: Um from a personal research perspective, I mean, I study um I study, I say I study obesity, I actually study body weight. Obesity just sits on one end of the spectrum. Um but in particular, I study food intake. And I I'm excited that over the next few years, two things, that we understand more about how humans control, how our human brains control our food intake. And everything about it, responding to stress or not, you know, um um being hungry or not. And this is and and not only me, by the way, the whole field is trying to to understand. So that's the first bit, trying to understand more about how our simple human brains, you know, influence why I prefer eating an apple versus an orange or something along those lines. Um but more crucially, in the computing power that therefore allows us to interpret this genetic data and how we interact with the environment. I'm hoping that we get to a point, so a lot of genetic testing companies that are out there at the moment claim to be able to take your genes and sequence them and and what have you and make predictions of what you can can or cannot do. I think many of them are overstating what they can what they can do. But I think that in the near future, 10 to 15 years from now, we will get far better of being able to look at our genes and try and personalize some element of of your diet, of your nutrition, or of your illness going forward. So I think that to to to my mind for my research is what we're really interested in. Within the what I want to do next from a broadcasting and nutrition and and um point of view, I still think that two things, regardless of us sitting here and having this really civilized conversation and an enjoyable conversation about about calories, this is we are still a minority in in in where we are now. And I think denying that is not going to help. And so you need to continue speaking, I need to continue speaking, and we need to continue talking about the importance of food in and of itself rather than anything else and the quality of food and eating eating eating food that is good for us and good for the soul. We need to do this not by demonizing food, but by loving food. And I think and I think we need this. And then the other side of things which I need to keep pushing is to destigmatize obesity, destigmatize the larger in our society and continue talking about weight stigma and about the fact that because of biological processes that for many people, body weight is really not a choice. So that that's what I'm hoping to do going forward.
Dr Rupy: Yeah, absolutely. I think that's definitely a a noble mission. Um you know, for too long
Giles Yeo: Whether or not I succeed is another question entirely, but that's that's the aim.
Dr Rupy: No, I thought I I'm sure you will. I mean, like certainly from the work that you've done on the BBC and your book writing and all the all the talks that I've I've been to as well pre-pandemic, you know, you're definitely getting the message out. And I think a lot more, particularly even on social media, I've seen a lot more acceptance of how it is wrong to assume that someone has a choice in obesity and how there are so many other factors at play. Um and you know, on the podcast, we we try and educate people on just the magnitude of inputs that lead to someone being larger than another person that are completely outside of their control as well. And I think, you know, further work on genomics like you were just mentioning, metabolomics, how we can actually uh measure what's going on in our guts, modulate that with dietary interventions as well as other lifestyle interventions for the betterment of health primarily. And then weight control, you know, as a as a side effect of really focusing on health. Um and and moving away from having further and further accurate measures of energy transfer and actually more towards, okay, what do I love eating? What is flavourful? What is culturally relevant? How do we celebrate food as a means of communicating across different
Giles Yeo: Love your food. And I think if we learn to love our food rather than fear our food, I think we'll go to a a we'll go a long way into into helping get ourselves better and healthier.
Dr Rupy: Definitely, definitely. Giles, been a pleasure. Thank you so much. I really enjoyed the chat uh at the start as well uh about American football. I'm not sure everyone else will agree, but that was great, man. That was awesome.
Giles Yeo: Thanks so much for having me.
Dr Rupy: To summarise our podcast today, we talked about the history of calorie counting and how we got to the measurements that have largely unchanged for about 100 years. The impact of individual differences and why the composition of food as well as the total energy intake is just as important. And if you want to have a bit more conversation around this, I highly recommend you listen to my conversation with Dr Nick Fuller, who is an obesity researcher in in Sydney, and we talk a lot about those other determinants of weight control and why it's not just about the calorie composition of your food. Um I I really think that's a great listen as well. We're going to be doing a bit more on this, particularly looking at food addiction and the other determinants of whether somebody is uh overweight or struggles with weight and everything in between. So I think you're going to find those podcasts brilliant. I hope you enjoyed it. Please do give us a five star review. Please share this with anyone who needs to listen to it, and I will see you here next time.
