Instant Genius - Eating for your genes - Giles Yeo

Episode Date: January 3, 2019

Dr Giles Yeo studies the relationship between our genetic make-up and how we’re eating, and knows that poor self-control isn’t entirely to blame for the obesity epidemic. He’s here to talk about how our genes influence how hungry we feel and how much we eat, and what we should do about it.  Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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combine handcrafted tradition with cutting-edge innovation and high-end materials, delivering digital precision with analogue warmth. So you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. I think the prevailing view is that the obesity is a simple problem because it is a disease of choice, which means that you just have to stop stuff in your face, mate, okay? And then you won't actually gain weight.

And in a way that's true, you can make a decision of yes or no. The problem is, if you are feeling slightly hungrier, if you are more attracted to food, if you feel the more rewarding elements of food, even just a little bit, it's always more difficult to say no. You're listening to the Science Focus Podcast from the BBC Focus magazine team. We're the UK's best-selling science and technology monthly, available in print and in several digital formats throughout the world.

Find out more at ScienceFocus.com or look out for us in your app store. Hello and welcome to the Science Focus podcast. I'm Alice Lipscomb-Southwell, the production editor of BBC Focus magazine. Giles Yo studies the relationship between our genetic makeup and how we're eating, and he knows that poor self-control isn't to blame for the obesity epidemic. In his new book, Gene Eating, The Science of Obesity and the Truth About Diets, he explains how our genes influence how hungry we feel, how rewarding we find food, and, as a consequence, how much we end up eating.

In this episode, BBC Focus editorial assistant Helen Glennie talks to Giles about exactly why being fat is so bad for us and whether some popular fat diets are worth following. He tells us how we should be eating in order to be as healthy, healthy as possible and whether we'll ever be able to fight the obesity epidemic with gene editing. Here's Helen talking to Giles Yo. So, Giles, you have a new book coming out called Gene Eating, The Science of Obesity and the Truth About diets. Can you tell me a little bit about what the book's about and what motivated you to write it?

I am an obesity geneticist. I work on the genetics of why some people are lean, obese, average size within the current food environment that we live in. So I'm interested in about biological variation of this. But it is, and that's fine, but it's clear that we are not going to be able to fix the problem with obesity unless we also understand the environments. Because after all, what we are, but an interaction of our genes, our biology, with the current environment that we're in. Okay, so that's the background in which I became interested.

I became interested in this. So the first part of the book involves just stating this fact. talking about what we know about the obesity problem and putting it in some perspective and providing some of the science that we have that has come out of my own research but also from our actual institute that I actually work in. But the vast majority of the book, however, then tackles the environment. And when I mean the environment, I mean tackles the diets that are actually being sold and peddled that are out there, that these folks that we study, that we study, that are more susceptible to being obese are being exposed to. And what the book is about is that every diet that's out there, or most diets that are out there, most of the fad diets that are out there, begin with a kernel of truth.

Okay? And they begin with a kernel of truth because otherwise people are not going to buy into it. It tends to be a person anecdotally saying, oh, I gave up X, I did Y, and I lost some weight. And so there is some kernel of truth there. But at some point, fantasy emerges. So really, what the book is, is trying to identify where the kernel of truth is, what the history behind it is, and at what point the fantasy actually emerges. And at all points, because of my genetics background, I try and inject, insert a genetic perspective about whether or not our evolution, whether or not anthropologically, sociologically, genetically, what our individual biology and genes have. actually played a role in how we then respond to these different guides.

So let's start with the genetics and the genetic variation within the human population. But first of all, can you give me a bit of a primer on how our bodies regulate our weight? It is the brain that controls our food intake, okay? And it needs two pieces of information in which to do so. The first piece of information is to know how much fat we have on board. And how much fat we have. Why is that important? Is that important? That's important because how much fat we have on board is how long we can last in the wild without food. Okay? So that's a pretty piece of important integer to hold in your brain. And it does this by having our fat release hormones. And these hormones circulate in the blood and our brain senses these hormones to figure out, okay, well, how much fat do we have? That's the first piece of information. The second piece of information that your brain needs to know is what you have just eaten and what you're currently eating. So in other words, this is short-term information.

And this information is obtained from hormones from the gut or from the stomach and the gut. So your brain needs long-term and short-term nutritional information and integrates these two pieces of information in order them to influence your next interaction with food. That's the primer. Okay. So what effect then do our genes have on that? Okay. So there are genetic modifiers that run throughout.

the entire process. Okay. And it depends what you're asking, right? It depends whether or not you're talking about body weight in particular. Are you talking about body shape and body size? But there are genetic modifiers, genes that influence both the secretion of the various hormones from fat or from the gut and genes that influence how the brain responds to these particular hormones.

So there are severe mutations that actually do occur. where if you block the signal, so for example, one of the key hormones that are produced from fat, for example, is called leptin. And leptin is one of the key fat hormones that signals to the brain how much and fat you have. And if you break that signal, if you stop the brain from being able to sense any leptin at all, then you end up being severely obese. It's very rare conditions that are actually out there, but they do exist. And the reason you end up being severely obese is because leptin's role is to let your brain know how much fat you have, yes, but is to actually turn on the starvation response when it disappears.

Because so leptin functions when it disappears from the blood. Because when it disappears from the blood, it means you don't have fat. And if you don't have fat, it means that you're starving. So it turns on a starvation response, which then makes you eat a lot because your brain thinks that you're starving. Okay. But that's very, very rare. But the pathways that actually triggers within the brain, the fat sensing and gut hormone sensing

pathways within the brain, that is where a lot of the very, very subtle genetic changes actually occur so that within the normal human population, we have a variety of different body weights. So conceptually, how does this work? The problem is there are hundreds of genes. So it really depends on which genes we're talking about. But simplistically put, just broadly and simplistically put, there are some people whose brains are ever so slightly less sensitive to the signals coming from your gut and coming from your fat so that it thinks you have slightly less fat than you actually do, or it thinks that you have eaten slightly less than you actually have. If you're slightly less sensitive, then you're going to eat more to make up for this fat that thinks you don't have, or make up for the food that thinks you haven't eaten. And these are very, very subtle.

They're not, you're not going to eat twice, you're not going to eat 10 times as much. Clearly not. You're going to eat a few percentage points more, right? A few percent more, you may feel a few percent more hungry, but you feel a few percentage points more hungry all of the time. And over a lifespan, this is what then happens. You then gain more weight than you are either severely obese, maybe your average size, maybe you're skinny.

And that pretty much is the biology of what we think is happening. with the genetics of obesity. So it is about food intake. So the biology and the genetics indicates it is about food intake. So it is still physics. Why we become fat is because we eat more than we burn. Where the biological variation, where the genetics lies, is in making some people more hungry than others.

So the physics of it, eat less, move more, is how we gain weight and how we lose weight. The biological variation lies into why. Why do some people feel hungry at another? Why do some people behave differently than others in the same environment? And therefore, eat more or eat less? So I think that we have this tendency to believe that weight is controllable and people who are overweight and obese are being lazy

or aren't exercising enough self-control or aren't getting themselves at the gym as much. So what you're saying here kind of disproves. that a little bit? Is there still a role, do you think, for self-control and discipline and things like that? Okay. So, I mean, you're right. I think the prevailing view is that the obesity is a simple problem because it is a disease of choice, which means that you just have to stop stuff in your face, mate, okay? And then you won't actually gain weight. And in a way that's true, you can make a decision of yes or no. The problem is, if you are feeling slightly hungrier if you are more attracted to food, if you feel the more rewarding elements of food,

even just a little bit, it is always more difficult to say no. Okay. So look, it doesn't matter how skin you are. Ask someone, you know, to stop eating when they're hungry. It is difficult, no matter how many six packs you have or I have a one pack. Okay. You know, how many packs you have because we are not evolved to stop eating when we're hungry. Okay. So this is what happens to someone who's slightly heavier. They feel slightly hungrier. They always find it more difficult to say no. Now, you can always say no, and many people do. And this is what happens when you do go on a diet and you manage to lose the weight. But the weight comes back on because you have to then, over a lifetime, right, continue to eating less in order to keep the weight, keep the weight off. So weight is the result

of a lifetime's decision rather than every single binary decision. So yes, it is a disease of choice, but it's like a weighted dice. It is always going to be more difficult to say no for some people. Okay. And what about the people that we see who seem to be able to eat as much as they want and never put on weight? Is there a role with things like metabolism? Is there a role for differences in metabolism in regulating weight? Yes, there is.

Okay, so twin studies, for example, have shown that if you can take identical twins and feed them exactly the same thing. and what happens is the identical twins will respond the same way to a specific diet, either dieting or eating too much, whereas if you take different sets of twins, they gain different amounts of weight even with exactly the same amount of food. Okay. So this definitely exists. But the differences are not as big as you might imagine, I guess, is the point.

What's interesting is when we actually look at the genetics that we know now, and it's by no means complete. The genes that we have identified, the genes that have appeared are almost entirely from the food intake perspective rather than from the metabolism and efficiency perspective. Why? Okay, does this mean that those genes influencing your metabolism don't exist? No, that's not the case. It just so happens.

It's more easy. It's easier to measure food intake because after all, you're measuring a piece of food going into the mouth. I mean, it's difficult on a population level, but it's easier to measure than it is to measure energy expenditure, right? Because that is just more difficult, it's just more difficult to measure. And when you actually do genetics, you need two things. You need numbers, many, many people, and you need a clean empirical measure. You need a measure that is not form of opinion, okay? And it needs to be clean. And which is why BMI is very easy to measure because you just need to know your weight and height. There's no imagination. There's no

opinion. Whereas when you actually deal with something like energy expenditure, it's just more difficult. So I think the genes are out there to be found. It's just that we don't have the tech to find it at the moment, but they will be found. That being said, and this is the critical thing, the maths are always going to be, the maths will always mean that food intake will always trump energy expenditure because you are always going to be able to eat quicker than you, you can burn the weight off. So a Mars bar or a chocolate bar, for example, what's 200 calories or something like that, roughly speaking, 240 calories?

I can eat a Mars bar in 90 seconds, if I'm motivated, right? It will always take me half an hour to 45 minutes on a treadmill or a bicycle in order to burn it off. So yes, undoubtedly there is a difference in our efficiency in dealing with calories and whether not we store or burn between people, but I think the biggest driver of obesity is still going to be food intact. Now, that's quite an interesting analogy with the Mars bar. You can eat it in 90 seconds, but it'll take you 45 minutes to burn it off. How much of that is a product of the changes in our modern environment?

Presumably we've got food now that's more calorie dense than we've ever had before, and we're moving a lot less than we used to. Is there an effect of that? Oh, undoubtedly. So that would be an example of the, of the environment, right? So I think evolutionarily, we were designed to be able to eat quicker than we can burn it off because we were never, because they never had enough food. We never had enough food. And so we got to the situation where we actually, as living beings, are quite efficient, you know, fuel consumption-wise. In other words, we can actually go pretty far compared to a car, for example.

We can actually go pretty far in terms of miles for any given gram of food that we actually eat. So we are designed to be efficient in order to live in a world where there was not enough food. It was only in about about 30, 40 years that we've had too much food. And having too much food has then driven the obesity epidemic. So it's the change in an environment, this moving less, eating more, the different types of food, energy deads foods that are there, which has driven the obesity epidemic. But whether or not we gain weight or how much weight we gain in this environment, that is where the genes play a role. So we know that being overweight or obese is unhealthy and it puts us at risk of things

like type two diabetes and heart disease. But what is actually going on inside our bodies when we put on weight? Why is it so dangerous? That's the $64 million question. And there are a number of things actually to handle, to actually think about them handle there. So it's why is being obese bad for you? Why is carrying too much fat bad for you? And I mean, I guess simplistically, you can look at it in a number of different ways. Not simplistically, obesity itself, too much fat in of itself, does not actually kill you. Well, it's not for most people anyway. I mean, you might get what we call gravity problems, so purely mechanical. So arthritis, things like sleep apnea. So in other words, because of too much fan, you can't actually breathe properly. And the fact that if you are overweight and obese,

you move less, and so therefore you don't actually exercise enough. But that is not what ultimately is the most dangerous thing. Ultimately, it's, broadly speaking, is what we call lipotoxicity. Lipo and fat, toxicity means toxic, meaning toxic, meaning you end up being poisoned by the fat. Let me just explain this, okay, where your fat is the safest place to store fat, so to speak, okay? It's the safest place to store the excess energy because that is a professional role. It's there to make sure that we live, that, you know, how long we will last in the wild without food. So it's very, very important to actually have these stores. What happens, however, when your fat stores become full? Now, just to be crystal clear,

when people become fat, they don't get more fat, cells, I mean, they may maybe a little bit, but you don't get more fat cells, you get bigger fat cells. Imagine your fat cells to be like a balloon. And as it fills up, it expands like a balloon. And then when you're actually burning energy, the balloon becomes smaller. That is how gaining weight and losing weight actually works. But at some point, the balloon becomes too full. So when it becomes too full, when it doesn't pop, that's where the analogy ends. What happens when your fat stores become full? Well, then the fat has got to go somewhere else.

And it is when it goes somewhere else, where it's not supposed to be, such as your liver, such as your muscles, that is when you tilt into metabolic disease. So that's the first thing. Your fat ends up not being in the fat and being somewhere else. Therefore, it actually causes disease and problems. So that is the primary issue. The big question is, hang on a second. Does everyone's fat expand to the same size? And as it turns out, the answer only very recently I'm thought about is no.

Okay? So in other words, carrying too much fat is bad for you. I think we can all agree that. But what is too much? Too much, as it turns out, differs from person to person. So in other words, everyone has a safe fat carrying capacity in terms of how big the balloon can get. But the size of the balloon is going to differ from person. to person, which is why you can get some skinny people with type 2 diabetes, right?

Because, well, I'm not fat. How come I've got type 2 diabetes? Because you have your genetic predisposition to the size of your fat cells that are smaller. So in other words, you get toxic fat in your muscles and liver at a far smaller fat size. Whereas on the other extreme, you get folks that get to, you know, three, 400 pounds and, you know, you watch it in the news or the tabloids where then the fireman has to, you know, drill a hole in roof in order to crane the person out, right? Now, they're very, very rare because for vast majority of us, if we get anywhere to that size, we would have died already of type 2 diabetes or cardiovascular

disease. So the issue is one of, yes, carrying too much fat is bad for you, but it's all about your personal fat carrying capacity. And the trick is, how do we tell? And that's difficult. So we don't know yet. It's the answer. There's some genetic clues, but it's your, so it's carrying too much fat, the fat in of itself, not being in the fat, that is what in effect drives metabolic disease. That is what is dangerous. Interesting. So yeah, that was going to be our next question. How do we know when we get to that point? But is that still just a bit of a mystery. That's cutting edge research. So that is people are, I mean, there are some hypotheses. There are people that are working on specific genes. But as a unifying answer, you know,

it's just difficult because so the answers we don't know, except for the fact that it is to do with safe carrying your personal fat carrying capacity. Actually, from the other perspective, and I think I should bring this up, given the fact that you don't actually have more fat cells, you have bigger or smaller fat cells, something like liposuction. This is why I think liposuction should be banned aside from a situation where you need it cosomically after you've done a surgery or you have a tumor, like a fat type of tumor, you need to actually remove that fat.

Why? Because if the Hollywood glitterati are trying to reduce the size of their bum or their boob or what have you, okay? If you actually remove fat through liposuction, you are reducing your fat carrying capacity, which means that, yes, you might be skinny with a small bum, but you are reducing your ability to store fat. So you're going to be just as ill. You're going to be metabolically, you may look great, but you're going to be metabolically just as ill if you use liposuction. I think liposuction should be banned as a cosmetic surgery for, you know, people who want to reduce their blood. thumb size. Oh, that's fascinating. Yeah, that makes it seem like a really terrible idea. It is a really terrible idea. I mean, so if you focus only on I want to look like Brad Pitt or

Angelina Jolie, that's a bad example because they're no longer together now. But if you want to, if you focus just on looking great, then I think you make bad decisions, is my view. Whereas if you think about the health of it, in other words, I want to try and increase exercise or something, and you don't worry so much about how you look that I think if you worry about your health, I think your weight will take care of itself. And so where does fat distribution around the body come into this? How come we can be similar weights and similar amounts of fat but be completely different shapes? So there are genetic studies out there which talk about body weight, shape and size.

So when we talk about pure BMI, so now it was independent of where it goes, then the genes that we look at tend to involve genes within the brain and they tend to involve food intake, okay, and feeding behavior. whereas your body's shape tends to involve genes within your fat, okay? In other words, and influence how your fat is distributed and how your fat actually expands, et cetera, et cetera. But as it turns out, not all fat is equal. Okay?

So, so, I mean, famously, you know, people who are pear-shaped, which means they have big bum, big, big thighs and what have you, and a small tummy, are healthier, in a veracomers, than someone who's apple-shaped, okay, who has a beer belly, for example. Now, men tend to put weight around their midrith, their belly, so-called visceral fat, whereas women tend, these are not exclusive, of course, women tend to put it around their bum underneath their, underneath their skin. And as it turns out, where you put your fat influences your metabolic health, because these are different types of fat, which secrete different types of hormones.

So where you put your fat does actually matter. Okay, so let's talk a little bit about these diets that you address in the book. Now, the first one that you go into is the paleo diet. Can you explain the rationale behind that? Where did that come from? So the rationale behind a paleo diet is that for the vast majority of humankind, and depending on who you look at, homo sapiens, probably two to three hundred thousand years old, any homo type of human in general, probably a million to a couple million years old.

Okay, we have been hunter-gatherers. Agriculture only emerged, what, 12,000 years ago or so ago. And so what the paleo community, this is their thesis, is that therefore we have not adapted to the agricultural diet. And what is the agricultural diet? Well, high amounts of grains, so carbs, okay, in effect. And then the other thing in which we're talking about is also the availability of dairy products, because clearly the availability of dairy products only came on after the domestication of animals, so after agriculture, and alcohol, because alcohol would only make sense once you had enough grain and had enough fruit in order to make alcoholic beverages.

So what the paleo people think is that, well, in order to be healthier, we need to eat a diet in which we're actually involved to eat. eat, which is a diet pre-agriculture. So therefore, any diet post-agriculture must be poisonous and must be bad for you. That pretty much is a general thesis of the paleo diet. Okay, so on the surface of it, when you explain it like that, that makes sense. So does it work? Well, I think then we have to think about what it actually means. Now, where's the kernel of truth?

Okay, once again, the paleo. It is undoubted that when we actually, when we, when archaeologists have looked at skeletons of early man at around the turn of the agricultural revolution that we were not healthy. Okay, so in other words, the adaptation to the agricultural diet was bad for us. On average, I think I read somewhere that, in fact, I wrote somewhere that we probably lost an average of something like four to six inches in height, and we had increased cavities, and we looked iller.

Okay, so this is where really the paleo thing has come from. There was a problem of adaptation. The issue is what did we have problems in adapting to? I think we had a couple of things. The agriculture meant that we had availability of a huge amount of starch, starchy-based items from grains, because that became available. In fact, still today, five grasses give us 50% of our calories, humankind gets 50% of their calories from five different grasses, rice, wheat, corn, oats, and barley.

And then depending on what culture you are, you focus on one of those things. I'm Chinese, I eat rice. And so there is that. And obviously, there's also the problem of adaptation to dairy, okay, where all of us can actually drink milk as kids, because we are, after all, mammals. But then the vast majority of the world are actually lactose intolerance because we stop being able to drink. to drink milk as adults. Okay? So there we go. There's the kernel of truth. But at the moment you begin to unpick the argument,

things start to fall apart. There are two issues with the paleo diet, okay? And they're big argument. The first argument is that we haven't adapted to the various diets that are available. But the answers we have. Humans are like cockroaches, okay? And we just adapt to what is there.

We are not adapted to a specific diet. We are adapted to be adaptable. That is the human, that is really what we're adapted to do. The second thing is that, well, therefore we have to eat something that's pre-agriculture. We have to eat the paleo diet. But that makes the singular assumption that there was one paleo diet. Well, there were people who were Inuit Eskimos. There were people who were living by the equator.

There were people who are in the Amazon. And why are they going to be eating the same thing? The Inuit are going to be eating seal blubber. the people on the serengetti are going to be eating something else, antelope, and the people in the Amazon jungle are going to be eating, I don't know, lizards. I don't know what they're going to be eating, right? There is no, this is the problem. There is no singular paleo diet, which is why the paleo diet doesn't make any sense.

The paleo diet, as it sits at the moment, involves things like eating lots of meat, lean meat, and eating no grains and eating no sugar and eating, it is a fantasy. Because the paleo diet, as the paleo, uh, practice, have it doesn't exist because we don't because there was no singular paleo diets. That's the first thing. The second thing is the foods that we eat today are all a product of agriculture. Even the meat we eat, okay, even the grains, even every single fruit we eat has been the product of agriculture over thousands and thousands of years. So even if you wanted to eat like paleolithic man, you can't because the foods don't exist anymore. And third is the adaptability. We have adapted. We have adapted to be

able to handle starch. We some of us have been adapted to deal with. with alcohol. Some of us have adapted to deal with digesting milk as adults. So those are the three reasons why I think the paleo diet is a fantasy. All right. And you talk about, you mentioned there that the vast majority of us, we can tolerate milk as kids. We need milk from our parents or from, you know,

wherever, but the vast majority of us become lactose intolerant as we age. I didn't realize that. That sounds, that's really interesting. Should, who should be drinking milk and eating dairy? Should we all be doing it? Should no one be doing it? How do we, how do we try and optimize our health around that? Okay. So, I would say, without quoting me exactly in the numbers, you are all going to quote me. About two-thirds of the world are lactose intolerance as adults. Now, lactose intolerance is actually a misnomer, okay, because we naturally become lactose intolerance as we get older. Now, the reason you might ask why, okay?

Well, I guess the whole problem is we are mammals, so we have to drink milk as kids. But if we don't, if we continue drinking the milk, then we get larger and we're still under boob or the teeth. And then the smaller, your smaller brother or sister can't get on and they die. Okay? So I just get the feeling that we need to be weaned under solid food so we can continue growing. And so that's probably the situation where we then become lactose intolerant so that we don't

continue trying to drink milk from mom. I think this is what it is. Clearly, I don't know proof for it, but if you told me to make a hazard a guess, I think that would be the situation. However, and this is a big, however, in terms of agriculture, okay, the moment people started having dairy herds, for example, cows or goats and sheep, okay, those three in particular, now clearly they would have been useful for meat and they would have been useful for fur or leather, okay? But people then begin to realize that, hang on a second, if we drink the milk from this cow or goat or sheep, we can get a lot more calories from this animal before we actually eat the animal and use the fur and use the leather.

And so in a time where there was not enough food, this became hugely, hugely selected for. But it didn't, it wasn't everywhere. So really, dairy herds were in a couple of areas in Africa and in, and in, and, and in northern and in northern Europe. Okay. And so when the actual original dairy herds that then appeared, then there was a huge selection for people that were able to drink milk. Every, all of the people in northern Europe that are able to drink milk have exactly the same mutation. And this mutation sits next door to the lactase genes. So lactase breaks down lactose. And lactose is the sugar found in milk, right? Because we can't break down lactose normally. We need lactase in order to do it.

In most people around the world, the lactase gene is then shut off as they go into adulthood. But the Northern Europeans and some populations in Africa have a small mutation that prevents the gene from being turned off. And so, and this same mutation probably happened in some gene carrier in northern Europe around the area, probably of a Denmark-y type of area, it was so selected for that it then spread throughout the entire northern Europe. So your ability to, well, I don't know what you look like. I'm making an assumption here. If you were Northern European, then your ability to drink milk will be biologically explained by this one little tiny, one little tiny change. Then you might ask the question, well, why can't my people, I'm Chinese? Why can't my people

and ring milk. And that's because we never had that same selection pressure. We didn't have dairying herds. We had we had different sources of protein. So in Chinese culture, for example, we would have, the Chinese, we mean the Chinese rather than me, would have first to domesticate the chicken and the pig. Okay, whereas daring animals were domesticated in the fertile crescent and moved into Europe. So the, and we don't drink pig milk and ick. And, and, and, and, and, And chickens, well, chickens have eggs. And so we eat the chickens and we eat the eggs. So there were a different group of animals that we domesticated first.

So therefore, we didn't adapt to drinking the milk because we didn't need to. Because we had other sources of protein. We had other sources of food that we were eating. Whereas Northern Europeans adapted to be able to drink the milk. The answer to your question about whether or not you should drink milk, if you can drink milk, drink milk. because we are all adapted to handle lactose, which is a sugar, like glucose, like sucrose. It's a sugar. It doesn't matter where lactose comes from, from mom, from a cow, from a camel, from a pig.

They're all the same sugar. So if you can deal with it as an adult, by all means, eat it. Clearly, if you have too much, you gain weight, and if you gain weight, you become fat, and that's bad for you. But that is another question. If you can actually handle dairy, then drink dairy. It's not bad for you. So, you know, you've explained that body weight is regulated by a whole bunch of different genes,

and it's very complicated. Do you think we're ever going to be able to get to a point where we can change our genes, where we can sort of reduce the issues that we're having with obesity through gene editing or any other process like that? I think it depends what we're talking about. Let's, for the moment, leaving aside ethics, okay, which is important. And I think whether or not we want to do this as a society, that is something broader. than something for weight gain.

So let's leave that aside for the moment. And let's assume that like IVF, society has come to accept it as regulated and accepted. Okay, let's just make that assumption for now. Then it all depends on what you're trying to change. Because if you're just trying to change one gene, so say, for example, if you had a terrible disease, muscular dystrophy or cystic fibrosis or some awful disease, if you had the opportunity to remove it from your family line forever, would you choose to do that?

Yeah, I think you would. I probably make that call and said, you know what? I don't want my son, my daughter to actually have this. And you may make the call to say, I want to change this gene from the mutant to the normal. But that is when you can only deal with one gene. The problem, as I said, with something like obesity,

is it's hundreds of genes. And at the moment, we do not have the technology to change hundreds of genes. We only have the technology, ethics aside, to change one gene. So I think trying to change a complex disorder is not going to be possible in the foreseeable future. But it probably is to change rare disorders that have to do with one gene in the near future. That technology is available now. So do you think that we might end up seeing people who have problems digesting or dealing with alcohol getting a little bit of gene editing

so that the hangovers aren't quite as bad. There we go. So that is where it becomes murky, right? Because if you're saying that, oh, I want to remove debilitating disease A, then I think most of us will go, yeah, I don't want debilitating disease A. But what happens if it's, I mean, what other single genes are there? Eye color. Okay, that's a single gene, right?

Blue, I want blue eyes. I would love blue eyes. Okay. What are the things? Boldness, depending, some boldness are, for I'm bald. I've got no hair, okay? For some people, it's down to a single gene. What happens we want to do that?

I want blue eyes. I want to be able to drink more. I want to be able to drink milk. It is going to be possible, undoubtedly. I think that is a question that we as society are going to have to make a call on. We have accepted, I mean, I use IVF as an example, because remember when IVF first started, people were thinking, terrible, as a test you baby. It's awful. But now, you're no longer to pariah.

You're a testy baby. You're a testy baby. It's just one of the ways for you to conceive, correct? People have, society has come to an acceptance of most sectors of society have come to acceptance. And I think we have yet to do that with gene editing. And I think we will need to. We will need to sit down and have that discussion about what is acceptable as society for us to want to change. But if you're asking, is it possible?

I think the answer is it would. will be in a very short term to change single genes. Should we do it? I don't know if I'm the person to answer that question. That was Giles Yo talking about how genetics influence our relationship with food. His book, Gene Eating, is available from seven dials now. In the Christmas issue of BBC Focus, we explore seven radical ideas that will expand your mind,

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