Thursday, 7 February 2008

Obesity 'may be largely genetic'. And the 23% that isn't genetic....?

On the news this morning*, we were told that obesity may be largely genetic.

There was some discussion about this today at work. I got the feeling (and I'm paraphrasing, probably unfairly here) that the general view was that the 'news' was a bad thing, because it might stop people dieting. I did mention that dieting didn't work anyway.

Apparently 'differences in body mass index and waist size were 77% governed by genes'. The rest of the BBC piece seems to go on to assume that the other 23% is governed by eating behaviour. Maybe it is. But the article didn't really say that - it only said that 77% was governed by genes. Some of the remaining 23% may be governed by prenatal factors, for instance, or breastfeeding, or childhood illness - who knows? Prenatal factors are particularly interesting. For instance, here's an article about the relationship between IUGR (slow growth in the womb) and adult obesity (babies with IUGR carried more fat as adults). Here's one about dieting during pregnancy (foetal undernutrition seems to lead to later obesity). There are loads of articles out there on this subject. Prenatal effects have to account for some of that 23% that isn't genetic.

So the BBC piece doesn't really tell us how much 'lifestyle' contributes to obesity - only that it's somewhere between 0 - 23%. As factors other than genetics are likely to contribute, it doesn't seem likely that lifestyle is responsible for the full 23%. This is hugely important, I think, and helps to explain why diets don't work.

We went out for lunch today, a rare event. Most people ate a fair bit, because most of them are starting diets next week. I ate a fair bit myself, and so was full up when the time came to order a desert. I was the only one who didn't have desert, but I felt under so much pressure to have one, oddly. It's very rare that I have desert anyway, as I don't have a very sweet tooth. I gave in, in the end, and had a taste of somebody else's desert. I don't know what all this meant, as I'm still getting used to being a fat person. I was by far the biggest person there, and yet I was the one who ate the least. The others seemed to really want me to eat more - why? Because they thought I secretly wanted to eat more but was too embarrassed to have any because I'm fat? They've seen me eat plenty of food on other occasions, though, so why would they think I'm ashamed of my appetite? Didn't they believe that I just wasn't hungry? Did they just want to include me in the group? Was my size irrelevant? I'd be really grateful for comments on this - why would people try to persuade a fat person to eat more, while at the same time showing that they disapprove of fatness (by talking about dieting)?

*It took me so long to post that I now mean yesterday morning.

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