Weighing the Evidence on Exercise

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. Until recently, the bodily mechanisms involved were mysterious. But scientists are slowly teasing out exercise’s impact on metabolism, appetite and body composition, though the consequences of exercise can vary. Women’s bodies, for instance, seem to react differently than men’s bodies to the metabolic effects of exercise. None of which is a reason to abandon exercise as a weight-loss tool. You just have to understand what exercise can and cannot do.
http://www.nytimes.com/2010/04/18/magazine/18exercise-t.html?ref=magazine&pagewanted=all