Weighing the Evidence on Exercise

“‘Anecdotally, all of us have been cornered by people claiming to have spent hours each week walking, running, stair-stepping, etc., and are displeased with the results on the scale or in the mirror,’ wrote Barry Braun, an associate professor of kinesiology at the University of Massachusetts at Amherst, in the American College of Sports Medicine’s February newsletter. But a growing body of science suggests that exercise does have an important role in weight loss. That role, however, is different from what many people expect and probably wish. The newest science suggests that exercise alone will not make you thin, but it may determine whether you stay thin, if you can achieve that state. ‘In general, exercise by itself is pretty useless for weight loss,’ says Eric Ravussin, a professor at the Pennington Biomedical Research Center in Baton Rouge, La., and an expert on weight loss. It’s especially useless because people often end up consuming more calories when they exercise. The mathematics of weight loss is, in fact, quite simple, involving only subtraction. ‘Take in fewer calories than you burn, put yourself in negative energy balance, lose weight,’ says Braun, who has been studying exercise and weight loss for years. On the other hand, if you can somehow pry off the pounds, exercise may be the most important element in keeping the weight off. ‘When you look at the results in the National Weight Control Registry,’ Braun says, ‘you see over and over that exercise is one constant among people who’ve maintained their weight loss.’ Scientists are ‘not really sure yet’ just how and why exercise is so important in maintaining weight loss in people, Braun says. But in animal experiments, exercise seems to remodel the metabolic pathways that determine how the body stores and utilizes food.”

http://www.nytimes.com/2010/04/18/magazine/18exercise-t.html