SEATTLE - Up to 35 percent of Americans are on a diet at any given time.

And with experts calling obesity an epidemic, losing weight seems more important than ever before.

But can you actually be fat and fit? Lisa Tealer thinks so.

At 300 pounds, she is -- by any standard -- obese. Yet this aerobics instructor says she's healthy.

"I actually believe that you can be fit and fat," she said.

The question has caused controversy in the wake of an obesity epidemic where 65 percent of the United States population is overweight.

"It's been proposed that this generation will have a shorter life expectancy than their parents," said Lisa Tartamella, a registered dietician.

But some experts say you'll live longer if you're overweight and active than thin and sedentary.

"Being completely sedentary, you are increasing your risk of cancer, coronary artery disease, diabetes, osteoporosis," said Paul Frickman, an exercise physiologist.

In one study, unfit men were much more likely to die of heart disease than fit men -- regardless of weight.

Another study showed that slender but inactive women were 55 percent more likely to die than women who were active and lean. But being both sedentary and obese raised their risk of early death by more than 100. Bottom line: There's no replacement for being active and lean, but even a little exercise helps.

"You will feel better and get those benefits of and, sometimes not the things that you see, but the things that you don't see, like lowering your blood pressure and lowering your blood sugars," Frickman said.

People who have excess flab in their abdomen are at especially high risk for obesity-related health problems.

If you do carry fat around your middle, losing just a small amount of weight can greatly improve your health.