Is obesity genetic?

Chris Smith put Omar's question to food expert Giles Yeo, from Cambridge University...

贾尔斯- Written is a very strong word. I think what is undoubtedly true is that our body shape and size, of which being obese is one element of that, has a powerful genetic element. Okay but everything all our traits have a genetic element the question to ask is how much of it is genes and how much of it is the environment? And your body weight and shape and size is a very very typical thing in which genes interact with the environment.

The bottom line is we know that obese people put very simplistically are obese because of a number of genes within the brain that make them more susceptible. You can't go against physics you have to eat more. But what happens is these genes tend to influence your feeding behaviour, your behaviour around food, making people slightly hungrier or slightly more driven to forwards food, they eat more, they gain more weight, therefore our difference in body shape and body size.

Chris - Do we know where in the brain those genes are exerting their effect? In other words biochemically if you're a carrier of a form of a gene that makes you more prone to overeating, where is that gene manifesting its influence?

贾尔斯- Because there are now over 200 genes that we know of that each subtly influence our interaction with food, they exist all over the brain. I mean some exist in an area called the hypothalamus in which it actually influences your actual hunger for food. So just tummy grumbling, I'm hungry. Others can sit actually in your higher your hedonic areas of your brain, your reward function, which influences the amount of reward the pleasurable feeling you actually get from food and others are going to be in areas of responding to stress and we know some people eat in response to stress, other people stop eating when they respond to stress. Same hormone, but yet we actually respondent in different fashions. And so all over the brain.

Chris - One question that springs to mind though Giles is that we're not evolving at a genetic level very fast. But in the last 50 years we've gone from the world population obesity being a rare phenomenon to obesity and overweight being a very common phenomenon as in some populations is more than half the population. That cannot be accounted for by changes in our genes. So what does account for this change in the prevalence of obesity in the population?

贾尔斯- So undoubtedly the environment and I use that loosely for anything that's not genetics so your lifestyle, your socio-economic class, what have you, that has undoubtedly driven the obesity. But what are our genes for other than to respond and adapt to the environment?

I'll give what one simple example, if there were two people. Okay. Two of me. And we stood next to each other and we looked exactly alike. We stood up, there is no difference between us but say we changed the environment and the environment is suddenly someone came along and pushed us both. Shoved me shoved my twin next door to me and I managed to tense my calf muscles up and stand still. Whereas unbeknownst to anyone the person next to me has no calf muscles. So the moment they're actually pushed they collapse.

So in one environment where they're not being pushed we look exactly the same. Whereas when you change the environment when the push comes when our food environment is in now suddenly the genes become unmasked. So the genes haven't changed they've always been there. It's just the way they react to the environment.

Chris - So returning to Omar's question which can we do anything about it. Is the intervention one not of a genetic intervention or some kind of drug but it's the environment that's to blame. That's what's changed. That's what we've got to change back.

贾尔斯- Yeah. We have to fix the environment that we actually living in. I mean there are drugs that are out there that can actually work for some people. And I think for the extreme cases in which you're Mrs. Smith you're type 2 diabetic if you do lose weight you'll die. Then I think there is a case for pharmaceutical intervention but for the most of us I'd like to think that we can really have a concerted effort to try and fix the environment that we're actually in.