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Is it genes or environment?

Watch an interview with Dr Giles Yeo on the topic of obesity in relation to genes and environment.
SPEAKER1: Hello, Giles. Thank you very much for joining us today for this talk, and we really appreciate this. And I’m sure–
GILES YEO: Thank you for having me.
SPEAKER1: I’m sure a lot of people know you already if not from your research then perhaps from a television, when you delivered a lot of very interesting documentaries on BBC Horizon, for example, around the obesity topic. But for those who didn’t have a chance to meet you before, would you mind just telling us a bit about yourself, about the field of research, and why are you studying, why are you researching obesity.
GILES YEO: So hey. My name is Giles Yeo. And I’m a geneticist, actually, based at the University of Cambridge. So I’m a trained geneticist. And what I do is I study body weight, of all things, and of which obesity sits on one end of the spectrum. And I guess the question is– you know, you’re studying the genetics of obesity. What does that actually mean? Is it not simply a matter of eating more, or eating less, moving less, moving more? I mean, isn’t it just, isn’t it just physics? And I guess the answer is yes. It is just physics that’s the how. How we get to the body weight we are is just physics. But why?
And that’s what I’m interested in. Why do people behave so very differently around food? Why do some people respond to stress by eating and other people respond to stress by not eating? These are diametrically opposite behaviour to exactly the same hormone, which is cortisol, the stress hormone. And so we now know that by studying the genetics of body weight we are by definition studying the genetics of how our brain influences our feeding behaviour. And so, because some people find it more difficult to say no because they’re more driven towards food for a myriad of different reasons, they eat more, and they are larger than someone else.
And so we now understand this is a large part of the reason why some people are small, medium, and large in the food environment we live in today. So that’s what I study, and that is my interest.
SPEAKER1: This is very interesting, and obesity is a very current topic. And, well, you are a world-renowned expert in obesity. So I was wondering whether you’d be able to answer this question that everybody is trying to answer. Why are we getting obese as a nation? Why are we getting bigger? But it’s not only as a nation, also globally. There’s been this paper published in “Lancet” a few years ago, and they investigated all the regions of the world, even those in developing countries. And what they observed is that every single region of the world has an increasing rate of obesity. So what’s your view on this global pandemic, which obesity is being called nowadays?
GILES YEO: I mean what is undoubtedly true, undoubtedly true, is that the vast burden of non-communicable diseases, non-infectious diseases, that we face today, obviously, we’re in the middle of an infectious disease pandemic at the moment, but the vast majority of non-infectious diseases that we as a human species face is diet-related. OK, now, this includes obesity, which is what we’re here to talk about. But also all of the associated illnesses, right, type 2 diabetes, high blood pressure, certain cancers, and all of the things we associate with obesity. So undoubtedly, a big part of the reason why obesity and all of its related illnesses is at the level it is today is because of the environment we live in.
A large part of it it’s going to be our diet. Now, that may seem an odd, that may seem an odd thing to be talking about giving that I’m a geneticist. They say, wait a minute, you haven’t said genes, you haven’t said genes. And that’s true. But look, what’s interesting is our genes haven’t changed over the past 30 or 40 years, which is when ostensibly when the obesity epidemic has actually risen. So how do I square this? How can I say, well, on the one hand, it’s actually the environment that’s driven the obesity problem, and on the other hand, I say that there are actually a huge amount of genetics playing into our feeding behaviour.
Well, so genes do not function in isolation. OK, so when a geneticist studies genes we don’t just study genes sort of in some ethereal, floaty, well, maybe some people do. OK, but at the end of the day, it’s actually genes interacting with the environment that results in our behaviour. So while the environment has driven the obesity epidemic today, whether or not we gain weight– because we remember not everybody is living with obesity in today’s environment. OK, there are some skinny people. There is some really big people, and there’s some average, in the middle of the road, people. So while the population average of obesity going up, it has to do with the environment.
How we have responded to the environment, that is where the genetics actually comes in. But undoubtedly, the cause of today’s obesity pandemic, obesity epidemic, whatever you want to call it, is the environment, and in large part, it is going to be our food environment
SPEAKER1: Well, you partly answered my next question here, which was, as you said, the environment, as this moderator, perhaps. And one of the key risk factors in obesity, but what is the roll of genes? Please explain why some people find it harder to lose weight than the others. And what’s the underlying mechanism?
GILES YEO: There’s two parts to your question. So let us handle the gene environment-interaction interaction first. It’s almost a little bit of a conflict in very many ways. Do people understand, well, is it an environment, or is it a gene? Is it, is it? Well, it’s both. So let me give you an analogy for this first part, OK. Imagine if I had a twin. I’m going to move over shuffle over here to my twin. It’s my turn, OK. So now in one environment we look exactly the same. Call this the 1950s. There was no serious obesity problem in the 1950s, OK. Now, so we look exactly the same.
Now, in another environment, call it 2021, the environment changes, and the environment change is you, matter, coming along and pushing me and pushing my twin. But, unbeknownst to you or to anyone else watching, my twin has a dodgy knee. So if you come along and you give me a shove, I tense up, I stay straight, I don’t fall over. Whereas my twin because he has a dodgy knee and you suddenly shove him, he goes– he falls down. So in one environment, the 1950s, where there was no push, the food environment was, shall we say, less toxic than today, all right. We look exactly the same. But when the environment changes.
When we’re suddenly in the modern food environment today, when you get the push, that is the modern food environment underlying genetic susceptibility. The dodgy knee as the analogy, suddenly, comes into play. The genes haven’t changed. He’s always had a dodgy knee, OK, but the push was never there. So suddenly, when the push happens, you collapse. So that is, that is how you kind of explain how come your genes appear to have changed. They haven’t changed. The environment has revealed the genes. Now, what do we understand about the mechanism? Well, as I’ve said, the genetics of body weight is fundamentally the genetics of how our brain influences our food intake, OK.
So now, our brain needs to know– so what are some of these genes? That’s going to be the next, obviously, the next question. What mechanisms are there? So these are going to be some of the mechanisms but definitely not all of the mechanisms. Our brain needs to know two pieces of information in order to influence our food intake. It needs to know, first of all, how much fat you have. OK. Fat are your long-term energy stores. And so this is critical because how much fat you have is how long you would last in the wild without any food. If your food sources stopped today– how long would you survive for? So and these are going to be hormonal.
Your fat secretes hormones. Your brain senses it. It can sense how much fat you have. Second, it needs to know what you are currently eating and what you have just eaten. Now, these signals are going to come from your gut. OK, so whenever we put in a piece of food, and we start chewing, and it goes down our oesophagus into our stomach and out the other side. Your gut secretes hormones all the way, all throughout the entire process, and your brain senses this. And these signals tell the brain not only how much you have eaten but what you have eaten. How much protein. How much fat. How much carbs.
So your brain senses how much fat you have, your long-term energy stores. And what you have recently just eaten your short-term energy stores. And then, influences where you– how hungry you might feel, your next interaction with a menu or restaurants. For some people, we now understand where some of the genes lie. It influences the sensitivity of your brains to some of these signals. So, for example, imagine I’m carrying around 20 kilos of fat, which is probably about right. But if my brain is only sensing 18 kilos of fat because it’s less sensitive, it’s going to think– I’m at 18 I thought I had 20, it’s going to drive you to eat more, so you get to 20.
But you already have 20 kilos of fat, so you’re going to end up larger than someone else. Equally, and maybe you’ll see where I’m going with this, now. If you’ve had 1,000 calories for lunch or dinner or whatever, but your brain only senses 900 calories, then it’s going to think, ooh, I’ve eaten less than I should. It drives you to eat more. So some of the mechanisms underlying why some people find it more difficult to say no, or more hungry or find it more difficult to get full, for example. It’s going to be down to the fact that your brains are just slightly less sensitive to these signals.
So those are just two possible mechanisms that are there, they are more that exist.

Giles Yeo MBE is a Principal Research Associate at MRC Metabolic Diseases Unit and a Scientific Director of the Genomics/Transcriptomics Core at the University of Cambridge.

His focus is on the study of obesity, brain control of body weight and genetic influences on appetitive behaviour. He has presented three BBC Horizon documentaries: Why are we getting so fat (2016), Clean Eating: The Dirty Truth (2017) and Vitamin Pills: Miracle or Myth? (2018). Giles was also a presenter on BBC Two’s Trust Me, I’m A Doctor. His first book, ‘Gene Eating: The Story Of Human Appetite’ was published in Dec 2018. His second book, ‘Why Calories Don’t Count’ was published in June 2021.

In this 2-part interview, Dr Giles Yeo discusses the environmental and genetic factors contributing to body weight and obesity.
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Nutrition Science: Obesity and Healthy Weight Loss

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