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The DNA of obesity

The tendency is to blame obesity primarily on poor food choices — sugary drinks, salty, greasy processed foods, staggering portion sizes.

But a growing body of research suggests that the appeal of these foods, as well as the drive to overeat, is rooted in our DNA.

Genome-wide studies have identified hundreds of genes associated with body mass index, waist-to-hip ratios and other traits of obesity, most of them expressed — meaning whether they’re turned on or off — in the brain.

Many of these genes evolved over millions of years to collect and store excess calories as fat whenever food was available, and to keep early humans from starving whenever food was scarce. Except as we’ve shifted from hunter-gatherers to farmers, then farmers to factory workers, food is no longer so scarce.

“In this part of the world, for most people, we don’t have famine anymore, we have only a feast,” says Dr. Sue Pedersen, of the C-ENDO Diabetes and Endocrinology Clinic in Calgary.

Instead of a survival mechanism, gaining excess weight is now a liability. And as scientists are discovering, some of us are more “genetically vulnerable” to packing on the pounds than others, says Macklin.

Part of this is how the brain responds to the hunger hormone ghrelin. In people with a genetic predisposition to obesity, the gut also tends to release fewer quantities of the hormones tied to fullness.

Either way, “If you take people who are the same weight and they have the same metabolic rate and you put everyone on (a) diet, people will lose weight unequally, based on their genetics,” says Macklin.