I exercise all the time, but I still have gut fat that hangs over my belt when I sit. Why isn't all the exercise getting rid of it?
It's a question many of us could ask. More than 45 million Americans now belong to a health club. We spend some $19 billion a year on gym memberships. Of course, some people join and never go.Still, as one major study -- the Minnesota Heart Survey -- found, more of us at least say we exercise regularly.
    And yet obesity (肥胖) figures have risen sharply in the same period: a third of Americans are obese, and another third count as overweight by the Federal Government's definition. Yes, it's entirely possible that those of us who regularly go to the gym would weigh even more if we exercised less. But like many other people, I get hungry after I exercise, so I often eat more on the days I work out than on the days I don't.Could exercise actually be keeping me from losing weight?
    The popular belief that exercise is essential for weight control is actually fairly new. As recently as the 1960s,doctors routinely advised against too much exercise, particularly for older adults who could injure themselves. Today doctors encourage even their oldest patients to exercise, which is sound advice for many reasons: People who regularly exercise are at significantly lower risk for all manner of diseases-- those of the heart in particular. But the past few years of obesity research show that the role of exercise in weight loss has been wildly over-evaluated. 
    "In general, for weight loss, exercise is pretty useless," says Eric Ravussin,exercise researcher at Louisiana State University. Many recent studies have found that exercise isn't as important in helping people lose weight as you hear so regularly in gym advertisements or from magazines.
The basic problem is that while it's true that exercise bums calories and that you must burn calories to lose weight,exercise has another effect: it can make one hungry. That causes us to eat more,which in turn can negate (使无效) the weight-loss benefits we just gained. Exercise, in other words,isn't necessarily helping us lose weight. It may even be making it harder.