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Biggest Gene Study Finds New Clues To Obesity, Apple Vs. Pear Shapes

(Wikimedia Commons)

(Wikimedia Commons)

You might think the link between genes and weight is simple: Fat tends to run in families, right? But as researchers tease apart the underlying genetics of body weight, it becomes ever clearer that it is a complex trait. Very complex, with ultimately perhaps hundreds of genes involved in what you see when you step on the scale.

Today, the biggest-ever study of the genetics of obesity, involving genetic samples from nearly 350,000 people, reveals dozens of new spots on the human genome that are involved with body weight and body shape, according to two papers (here and here) published in the journal Nature.

My dominant impression: The data tend to implicate the brain as a powerful influence on overall body weight, but point more towards hormones and the fat cells themselves as strong determinants of whether we’re shaped like “apples” — with more upper body fat — or “pears,” with more fat concentrated below the waist.

Dr. Joel Hirschhorn, of Boston Children’s Hospital, the Broad Institute and Harvard Medical School, leads the Genetic Investigation of Anthropometric Traits consortium, or GIANT, the friendly collaborative of hundreds of researchers around the world who contributed to the studies. Our conversation, lightly edited:

How would you sum up the findings that come out in “Nature” today?

We did a very large genetic study looking at two different kinds of obesity: Overall obesity measured by body mass index and central obesity — fat around the belly — measured by waist circumference and hip circumference. And what we found was that there are a lot of genes that influence both types of obesity, but, really interestingly, the types of genes that influence overall obesity are actually quite different than the types of genes that influence where the fat goes on the body.

Interesting. So what does that tell us?

That tells us that even though both types of obesity are bad for your health, that it may be very important to understand what kind of obesity you have, because if the biology is different, that means the way we can treat that obesity, or prevent it effectively, is probably going to be different for the two kinds of obesity.

So it may matter even more than we thought whether you’re shaped like an ‘apple or a ‘pear’?

That’s right. It matters both whether you’re an apple or a pear and it matters just how big you are in general. But the way you get to be big in general is probably different than the way you get to be an apple or a pear.

So it’s different pathways? Perhaps whole different mechanisms at work?

That’s right. The overall obesity seems to have more to do with what’s going on in the brain, maybe controlling appetite or whether you get full or how quickly you get full. And the apple vs. pear seems to have more to do with your fat cells and hormones that your body makes, things like insulin.

So does all this translate into any action points for the general public? Continue reading