Giles Yeo: extreme genes

Cambridge University geneticist, obesity expert, author and BBC presenter Giles Yeo tells Chris Smith a bit about his science...

Giles - I am a geneticist and a perfectly upstanding thing to do. You know, my mother in law still speaks to me. So this is a good thing. But people often use genetics to study a trait or a disease. And I happen to study body weight. And actually the moment I say body weight, obesity actually, which is one end of the spectrum, I suddenly become the bad person and I become the bad person because I'm perceived as giving fat people, overweight people, people with obesity an excuse - which is always an interesting take because if I was studying the genetics of cancer, would I be giving the cancer patient an excuse? I wouldn't. And the reason why I'm "bad", is because people say, "Well you eat too much. That's why you're the size you are. You eat too much. Right?" They say that to me.

Chris - They say that to you?

Giles - Thank you. I've lost weight. I want to point out when I was vegan!  Anyway, so "they eat too much" and that is true. Your body weight is going to be down to how much you eat and how much you burn. Right? But the question to ask is why? And at the end of the day it's because different people behave very, very differently around food and there is a lot of genes that are actually involved.  The physics is the first law of thermodynamics. You can't magic the calories in and magic the calories away, but it's working up to the physics. Why we actually get to the physics we get, why we eat too much. That's where the biology is. And I think by studying extreme cases of obesity, so these are not going to be normal cases of obesity. These are three, four year old children who are 40, 50 kilograms. Okay, so that's a lot. That's a lot of weight. I'm 75 kilograms. For example, one of the pathways we know that are disrupted in severe obesity is the fat sensing pathway, where because there's a lack of a signal from the fat to the brain, the brain doesn't know that you have enough fat on you and so you continue...

Chris - And that is genetic? That is a genetic reason why your fat doesn't talk properly to your brain and that makes you eat too much?

Giles - Exactly. There's a hormone there called leptin, and when there is actually a mutation in the hormone leptin then and you don't have any leptin, then your brain doesn't know how much fat you have. 

Chris - The thing is Giles, why I'm slightly skeptical, and you can probably disabuse me of my skepticism, is that 50 years ago the number of people who were overweight and obese was vanishingly small and now it's very, very large. Now we're not evolving that fast, are we?

Giles -We're not evolving that fast.

Chris - Why is there a difference?

Giles - Well, so here's the thing. Whenever people study and talk about genes, they think that geneticists only look at the genes in of themselves and we do look at the genes, but we have to look at the genes in context with the environment. It turns out that every single human trait as including our body weight has a genetic influence. Every single trait and behaviour. The trick is to ask what role the environment plays. Now your genes, as you say, they're empirical. You're born with them, you die with them. They don't change anywhere in between, but the environment does and as the environment changes, the way your genes express themselves and change actually then that changes as well. And so what has happened is as we get to the stage where we're at, we have too much food today. I think that's not, that's not anything to debate. Suddenly, it has unmasked susceptibilities of certain people you know who are going to eat more in the environment. Whereas in the past there was just not enough food around for people to eat too much. Whereas now there is ample opportunity for people there to take advantage of the environment or not advantage depending when you look at and actually get too large.