If you think cardio is the key to blasting belly fat, keep reading: When Penn State researchers put dieters into three groups-no exercise, aerobic exercise only, or aerobic exercise and weight training-they all lost around 21 pounds, but the lifters shed six more pounds of fat than those who didn't pump iron. Why? The lifters' loss was almost pure fat; the others lost fat and muscle.
Other research on dieters who don't lift shows that, on average, 75 percent of their weight loss is from fat, while 25 percent is from muscle. Muscle loss may drop your scale weight, but it doesn't improve your reflection in the mirror and it makes you more likely to gain back the flab you lost. However, if you weight train as you diet, you'll protect your hard-earned muscle and burn more fat.