American waistlines just keep expanding. A new report finds obesity levels rose in 28 states last year. But, despite the rising levels, there is a growing awareness that obesity is a major health problem.

In 1980, 15 percent of American adults were obese. Today, that number has doubled.

Trust for America's Health, a non-profit group, has just issued its seventh report on obesity in America.

Jeff Levi is one of the authors:

"In 1991, there wasn't a single state that had an adult obesity rate over 20 percent," said Jeff Levi. "Now 38 states have adult obesity rates of more than 25 percent."

Since last year, four more states reported adult obesity rates of more than 30 percent - meaning that at least 30 percent of their populations are obese.

"There are many explanations," he said. "One, is we are just much less active than we used to be. We've built our society around cars, around being inactive."

Studies show a link between time on a computer or in front of a TV and obesity.

Other studies point to high calorie fast food.

But Levi says there are other risk factors.

"Obesity is very much associated with poverty," said Levi.

Fresh fruits and vegetables, lean meats and fish are expensive. And there are few grocery stores in low income neighborhoods. That means poor people find it difficult to buy healthful food.

"And poor people also tend to live in neighborhoods that are less safe and have fewer opportunities for physical activity," he said. "So the combination of eating more calorie-dense food and having fewer opportunities for physical activity, that's what creates this obesity epidemic."

Levi praises the Obama Administration, and First Lady Michelle Obama, for trying to change eating and exercise habits.

"It's threatening our children," said Michelle Obama. "It's threatening our families and, more importantly, it's threatening the future of this nation."

The first lady has traveled the country in her campaign against childhood obesity.

Last year, the Obama Administration pledged more than $400 million to help bring more grocery stores to underserved communities nationwide.

The obesity crisis means more spending on healthcare.

The US Centers for Disease Control reports that obesity costs at least $147 billion annually, and that figure is based on data from 2006.

Kenneth Thorpe of Emory University expects the number to go even higher.

"It's the single biggest driver over the past 10 to 15 years of why healthcare has risen," said Kenneth Thorpe. "We do have this explosion of chronic diseases related to obesity."

Diabetes, high blood pressure, heart disease and cancer are linked to obesity.

Health policy experts and doctors hope the reports will help Americans change their lifestyle.

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