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Why Diets Make You Fatter -- And What to Do About It

The $60-billion-per-year diet industry keeps offering new programs and plans, but it doesn't work 95% of the time because the problem is more than calories.

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Beyond the psychology of dieting and our largely inherited physiology, we're still driven by the evolutionary pressures that drove our ancient hominid ancestors -- hunters and gatherers, who had to make the most of every bite to survive. Sometimes their food was plentiful, but during times of scarcity, their bodies adapted by lowering their metabolism to conserve every calorie consumed. Following a period of scarcity, their bodies became even more efficient at storing fat in preparation for the next famine. These fat-layered bodies, better able to adapt to scarcity, were likelier to reproduce. As a species, therefore, we've inherited a predisposition to hold onto fat after each period of scarcity. Today, our bodies can't distinguish between hunger caused by famine and hunger caused by a self-imposed diet -- and they react to the latter as if it were the former. The "failure" of diets is actually a "success" in terms of species survival!

When dieting for weight loss, our bodies respond to the perceived famine by feeding off fat and muscle. Muscle is the metabolically active part of our body: the more muscle we have, the more calories we can burn. Since every weight-loss attempt includes the loss of both fat and muscle (but what's regained is only fat), dieters burn even fewer calories, which makes it easier to gain weight and results in a higher fat-to-muscle ratio. Repeated dieting attempts may significantly increase the percentage of body fat over time. In fact, in 2007, Traci Mann and her colleagues at UCLA conducted a comprehensive and rigorous metanalysis of 31 long-term studies of obesity treatment for Medicare patients. They found that despite losing 5 to 10 percent of their starting weight in the first six months, the vast majority of dieters had regained all the weight -- and within four or five years, one-third to two-thirds of subjects had regained more weight than they'd lost.

In 1993, after it was discovered that less than one percent of dieters could maintain their weight loss for five years (the criterion for success), the Federal Trade Commission charged 17 companies, including Weight Watchers, Jenny Craig, and Nutrisystem, with making false and deceptive claims about the safety and efficacy of their programs. While many programs claim that they aren't diets, whenever food is manipulated for the purposes of weight loss, it is, in fact, a diet, and not one of them has produced research demonstrating long-term results.

The pitfalls of diets have been known for decades. Not only does dieting make people fatter: it affects psychological health. In a classic study during the 1940s, researcher Ancel Keys studied 36 conscientious objectors to see what would happen if they were placed on a semistarvation diet for six months. The men were given nutritionally adequate food, with the same calories as most commercial weight-loss plans. The changes observed were dramatic. In addition to losing about 25 percent of their body weight, they experienced noticeable personality changes, becoming lethargic, irritable, depressed, and apathetic. They became obsessed with food, and they talked constantly about eating, hunger, and weight.

Once the men had begun the refeeding portion of the study, restrictions were no longer placed on their eating. They binged for weeks, often consuming food to the point of feeling ill. Despite their overeating, they continued to report feeling ravenous. The weight previously lost returned rapidly as fat, and most of the men lost the muscle tone they'd had prior to the experiment. Some of them ended up weighing more than they had before the start of the study. Their emotional stability and energy returned only after they'd regained the weight.

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