The idea of specific populations predisposed to obesity is encapsulated in a notion now known as the thrifty gene-technically, the thrifty-genotype hypothesis-that is now commonly invoked to explain the existence of the obesity epidemic and why we might all gain weight easily during periods of prosperity but have such difficulty losing it. The idea, initially proposed in 1962 by the University of Michigan geneticist James Neel, is that we are programmed by our genes to survive in the paleolithic hunter-gatherer era that encompassed the two million years of human evolution before the adoption of agriculture-a mode of life still lived by many isolated populations before extensive contact with Western societies. "Such genes would be advantageous under the conditions of unpredictably alternating feast and famine that characterized the traditional human lifestyle," explained the UCLA anthropologist Jared Diamond in 2003, "but they would lead to obesity and diabetes in the modern world when the same individuals stop exercising, begin foraging for food only in supermarkets and consume three high-calorie meals day in, and day out." In other words, the human body evolved to be what Kelly Brownell has called an "exquisitely efficient calorie conservation machine.
( Gary Taubes )
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