More bad news about Americans' waistlines: They're only going to get bigger.

Already, about a third of people are obese. By 2030, it is estimated 42 percent of the population will be.

The latest government data show that obesity is leveling off after big rises in earlier decades. But the new study finds even small continuing rises will add up.

Duke University researchers predict that by 2030, 11 percent of people will be severely obese, roughly 100 pounds or more overweight. That's double today's rate.

The obesity epidemic is fueling diabetes, heart disease and other ailments - and adds significantly to the nation's rising health care bill.