November 10, 2005

Overweight? Sorry, it's in your genes. Over breakfast, Jeffrey Friedman nibbles on a sliver of papaya and an unbuttered English muffin. A tall, rangy fellow, he is one of the leading scientific experts on obesity. Obviously, it's not a problem for him personally. "Right now, I'm about five pounds heavier than I want to be," he says. "But it's almost impossible to lose the weight."

Dr. Friedman is the man who discovered a hormone he called leptin (from the Greek word for thin). Leptin is instrumental in regulating weight. When you store a lot of fat, leptin sends a signal to the brain telling you to eat less, and vice versa. "There's a powerful system that balances your energy with great precision. It's a classic feedback loop, like the one that regulates your blood sugar."

Certain obese people have a defect in the feedback loop. This self-regulating system -- and not your pathetic lack of willpower -- explains why you're doomed to keep losing and gaining the same 10 pounds. "People think that all they have to do is eat less and exercise more. But the system that regulates their weight is unconscious."

This isn't the way society sees it, of course. We have funny attitudes about root causes. We have, humanely, decided that many unfortunate conditions, such as mental illness, have powerful biochemical origins. But we don't see weight that way. When it comes to weight, we still blame the victim. Sure, a few people exist who've managed to lose 100 pounds and keep the weight off. But, in general, trying to turn a fat person into a thin one is as futile as trying to turn a short person into a tall one.

Like height, weight is highly heritable, and beyond a certain narrow range -- 10 or 15 pounds -- you can't change it. If the principal regulators of weight are biological, rather than environmental or behavioural, then public campaigns nagging fat people to slim down are useless. You might as well try to cure cancer by telling patients to eat more broccoli and cheer up. "The command to eat less and exercise more has never been shown to work at a public-health level."

For the record, Dr. Friedman is not endorsing couch-potatoism. Exercise and healthy eating are good things. Obesity is a serious problem with serious consequences. But the most promising treatments will come from the research lab, not from suing McDonald's.

As someone who gained and lost the same 10 pounds for years, I can attest that my leptin feedback loop is in tip-top shape. But I'm curious about another thing. Where is the obesity epidemic? As I walk down the street or look around the office, I can't see it. Sure, there are a fair number of people who are conspicuously overweight -- but not anything like 20 per cent or 30 per cent of the population, or whatever number the latest study has trotted out for the headline writers.

Dr. Friedman doesn't see it, either. He says the fat epidemic has been wildly overstated. Careful statistical analysis shows that thin people are just as thin as they were in 1991. People in the middle of the range have gained six or seven pounds. Only at the top of the range, among the massively obese, have people packed on substantially more weight. The bell curve of weight has moved slightly to the right, and more people have crossed the line that experts use to divide the "normal" from the "obese." But the average weight gain is only seven to 10 pounds.

Some day, scientists will unlock the biological key to weight control. Meantime, as I chat with Dr. Friedman over breakfast, I succumb to the urge to slather jam on my English muffin.

I feel vaguely guilty. But now I know my leptins made me do it.