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Skinny genes: How DNA shapes weight-loss success Add to ...

Stephen Scherer is a nice guy: smart, funny, very easy to like - unless you're eating lunch with him.

He can put away a cream soup and a platter of penne with Italian sausage and wash it all down with a large Coke. And even though he's 47, and driving his son to hockey is the closest he comes to rigorous daily exercise, he's still as trim as a teenager. Which is why, if you're the type to pay by the pound for any extra indulgence, you might be tempted at some point during the meal to stab him with your fork.

But you can't blame him. Dr. Scherer simply has skinny genes.

A leading geneticist at the Hospital for Sick Children in Toronto, he recently analyzed his own DNA and discovered that he inherited a rare genetic quirk from his mother that seems to give him a speedy metabolism, allowing him, he suspects, "to eat like a pig and never gain weight."

"I've been the same weight for about 20 years. It never fluctuates more than a few pounds," he says. "I think I probably would exercise more if I knew I needed to."

Most of us haven't been as lucky in the DNA draw. Almost two-thirds of Canadians have tried losing weight during the past five years, but most fail to keep it off, according to a survey released this month by the Heart and Stroke Foundation. Yet a growing body of research has found that much of our success in losing weight, whether it's resisting the urge to overeat or exercising, is shaped by our genes. Studies suggest that genetics account for 60 to 84 per cent of a person's body mass index. The most compelling results come from work on identical twins, who not only share identical genomes, but also nearly identical weight profiles - even when they are raised in different environments.

"We know that genetics plays the dominant role in determining body mass index," says Arya Sharma, one of the country's foremost obesity researchers at the University of Alberta. "I can tell your risk of obesity by looking at your parents."

After running DNA scans on thousands of people over the past few years, researchers have uncovered about 50 gene variants related to the propensity to gain weight. Each one of these variants can moderately influence body mass, but some of us lug around more of them than others.

"Exercise will not help everyone lose weight," Dr. Sharma says. Although slimming down is just one of many reasons to exercise, he notes that "the more genetically predisposed you are to gaining weight, the more effort it's going to take to override those genes.

"Just go out on to the street and pick out 100 people at random - give them the same food to eat, the same amount of exercise, and some will gain weight and some will lose it. Even whether or not you like exercising is very strongly genetically determined."

But before anyone concludes that diet and exercise are futile weapons in the war on weight, researchers have also found that the simple eat-less, move-more strategy can overcome the known genetic susceptibilities for excess weight. Some people just have to move much, much more and eat far, far less to see results.

"There is no gene related to obesity we know about so far that cannot be overridden by lifestyle choices," says Robert Hegele, who has studied and discovered many of the genetic underpinnings of cardiovascular conditions at the University of Western Ontario. "In my career of 25 years, I've only met about five people for whom diet and exercise do very little."

Dr. Hegele says this holds true even for people who carry two copies of the FTO gene, the most significant obesity-related gene identified to date.

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