Is there such thing as inheritance of obesity, or the tendency to become overweight? If there is a gene that has some control over weight, can external factors change the dominance/expression of your parents' alleles in you? For example, if your mother is a large woman and your father is thin-framed, and you are somewhere in the middle, can external factors make one parent's allele dominant and expressed over the other? Could a sudden change in lifestyle trigger a change in genetic expression?
We put this to Giles Yeo, from the MRC Metabolic Diseases Unit...
Giles - There is definitely inheritance of body weight and body shape. The question, however, appears to assume there’s only one inheritance, one inherited possibility but there isn’t. It’s not just one gene, it’s not just one fat gene. We now know of over 100 genes that actually involved in determining your body size.
The second part of the question about the role of the environment. That’s a very good one because our genes haven’t changed, certainly over the past 30 years, whereas obesity has skyrocketed, and that is down to the interaction between your genes and the environment. I think the analogy I alway use is that if two genes (two people) are standing side by side, they look exactly the same. Suddenly an environment comes along, say me, and I give someone a shove and the other one not a shove, someone will fall over and someone won’t, and that’s because they’re interacting with the environment in a different fashion.
Chris - In our sort of caveman era, we would have had enormous advantage conferred upon us if we had genes that made us store energy for a rainy day. Whereas now, you have Waitrose, Tesco’s, Sainsbury's, other supermarkets are available just down the street and you can go in there any by anything you want.
Giles - It’s not only walking in to do, you can now order anything from your smartphone.
Chris - That’s true and you can have it delivered to your house, can’t you?
Giles - Exactly, you don’t have to get your bum out the door.
Chris - So you can be physically too big to get out the door and you still get fed, which means it become maladaptive, doesn’t it?
Giles - That’s correct.
Kat - And one of the really fascinating things… I’ve just been making a radio programme looking at how changes really early on in development affect the health, the lifestyle, and even the weight of people much, much further down the line. So there is the important role right at the start of development, maybe even before a woman knows she’s pregnant herself, that there could be influences there from the mother, and maybe if the mother’s not got enough food.
There’s a very famous example of a famine in Holland during the Second World War, where the babies were exposed to this famine very, very early on in the womb and they came out kind of OK, but then later on in life they were fatter. Maybe because they thought, oh we’re starving here, we’d better make the most of everything we’ve got.
Giles - So what you were referring to is known as the “Dutch Hunger Winter,” and the field of studying this is “in-utero programming.” And what that studys is, when you’re actually carrying a baby, is there any programming that happens, and there is. And the reason there is is because what you want to do, as a foetus, is to predict what the environments going to be and get yourself set up the best way that you're going to be.
You’ve got genes which don't change, but if you actually change the markers on the genes, it actually changes the way genes are turned on and genes that are turned off and so there is definitely evidence for that.
I have to say though that the evidence for the obesity side of things, and programming is not huge. The evidence for type 2 diabetes, and insulin resistance, and other metabolic diseases… definitely, definitely so. And more scarily, people are now beginning to say, before you even become pregnant is that having an unhealthy diet can actually influence your egg and your sperm. Not together in the same person, clearly but an egg and your sperm…
Chris - It would be very strange if you did.
Giles - But there are now studies happening of how can an unhealthy diet or lifestyle influence your egg and your sperm.