In studies that challenge decades of accepted wisdom about caloric intake and weight control, scientists are finding that calories from fat are uniquely fattening. Eat a fat-rich dessert such as premium ice cream, and you will, as the saying goes, apply it directly to your thighs.

But replace fat in your diet with carbohydrates, and it'll be easier to maintain your weight. Even if you occasionally eat a little more than you really need, your body will have a hard time turning the excess carbohydrates into body fat. Calories from protein and carbohydrates even speed up metabolism and thus help in maintaining weight.

No one is saying, of course, that we can eat unlimited carbohydrates and never get fat. For health, we're also better off with complex carbohydrates, such as vegetables, grains and beans, than foods packed with sugar. And recent diet-cancer research suggests excess calories, from whatever source, may promote tumor growth. But if you watch your calories, exercise and eat a low- fat, high-carbohydrate diet, you'll stand a good chance of getting lean and staying healthy.