The world is in the grips of an obesity epidemic. Scientists have spent hundreds of millions of dollars trying to understand the metabolic, genetic and neurological foundations of why we keep gaining so much weight. But, as David H. Freedman writes in "How to Fix the Obesity Crisis" (Scientific American, February 2011),you do not have to know everything there is to know about the physiological aspects of obesity to grasp a few simple concepts of how to lose weight.

In his article Freedman shows how the concepts of behavioral analysis underlie most successful programs for losing weight. Take our poll to see how your weight-loss attempts compare with other survey-takers. At the end, you will learn about four general rules of thumb that researchers believe increase the chances of losing weight and keeping it off.

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