BOSTON -- With more than half of Americans over their ideal weight, experts say there is an obesity epidemic sweeping the nation.

NewsCenter 5's Heather Unruh reported that conventional thinking says too much eating plus not enough exercise equals fat stomachs. But what if this obesity equation was wrong -- what if you could "catch" obesity -- like you "catch" a cold?

"A lot of people think we're really nuts," said Dr. Richard Atkinson. "A virus causing obesity? There's a great deal of skepticism.-"

In his work at the University of Washington, Atkinson made a discovery. A virus known as AD 36 can cause fat cells to be produced at an accelerated rate. He tested the idea in animals.

"I can absolutely, certainly say that if you are a chicken, a mouse or a monkey and I squirt this virus up your nose, you've got a better than 80 percent chance of getting fat," he said.

The virus, he says, is one of 50 adenoviruses common in people. And, Atkinson said, it's contagious. No wonder, he said, that the country has an obesity epidemic, an epidemic that is spreading to places like Asia, which once had a low rate of obesity.

"Now that people are starting to travel to China, the prevalence of obesity has exploded," said Atkinson.

The idea that a tiny germ could cause a large problem is not unprecedented. Until recently, medical professionals thought ulcers were caused by spicy food, but now they know most are the result of a bacterial infection. And doctors now know almost all cases of cervical cancer are the result of a virus.

So Atkinson designed a blood test for this fat virus and found that 30 percent of the obese tested positive, compared to 10 percent of those who were not overweight.

"We think that everyone ought to have this test, just like you have a serum cholesterol," he said.

"For me, it seems premature that people will be obtaining this antibody test," said Dr. David Stone, an infectious disease expert at Tufts New England Medical Center.

And a waste of money, according Stone. He said larger studies are needed to prove this virus causes anything and believes if there were something to this idea, the pharmaceutical industry would have jumped on it long ago.

"I don't think you could catch obesity like a flu virus or a common cold virus," said Stone.

Some nutritionists NewsCenter 5 spoke to say this idea of a virus will only distract Americans from the work they need to do to prevent obesity -- eating right and exercising. That' s one equation, they say, that has been tested and works.