Strolling to the bus stop, fidgeting during a meeting, standing up to stretch, jumping off the couch to change channels and other seemingly minor physical activity can make the difference between being lean and obese, according to a small study of self-described couch potatoes.

The most detailed study conducted of mundane bodily movements found that obese people tend to be much less fidgety than lean people and spend at least two hours more each day sitting still. The extra motion by lean people is enough to burn about 350 extra calories a day, which could add up to 10 to 20 pounds a year, researchers found.

"There are these absolutely staggering differences between people who are lean and people who are obese," said James Levine of the Mayo Clinic, who led the research being published in today's issue of the journal Science. "The amount of this low-grade activity is so substantial that it could, in and of itself, account for obesity quite easily."

Perhaps more importantly, Levine and his colleagues also discovered that people appear to be born with a propensity to be either fidgety or listless, indicating it will take special measures to convert the naturally sedentary into the restless.

Levine, it should be noted, is no couch potato and certainly not overweight. He spoke by telephone while walking 0.7 mph on a treadmill in his office, where he set up a computer above the machine so he can walk and work at the same time.

"Some may say this is a story of doom and gloom, that people with obesity have no choice. ... I would argue exactly the opposite," Levine said. "There's a massive beacon of hope here."

Other researchers agreed, saying the new study, while small, provides powerful new evidence that a major cause of the obesity epidemic is the pattern of desk jobs, car pools, suburban sprawl and other environmental and lifestyle factors that discourage physical activity. And despite generations of parents' admonitions to the contrary, people should be encouraged to fidget.

"Figuring out ways to increase physical activity — not necessarily getting people jogging every day but just building physical activity into a person's day — are reasonable strategies that have the promise to combat this epidemic of obesity," said William Dietz of the federal Centers for Disease Control and Prevention.

The number of Americans who are overweight has risen substantially in recent years, with more than two-thirds now overweight or obese, raising the prospect of an epidemic of heart disease, diabetes and other weight-related ills.

Levine and others have done earlier studies suggesting a dearth of routine activity may be part of the problem, but the new study is the most exhaustive to date.

The researchers recruited 10 mildly obese and 10 lean people to wear special underwear, which used technology developed for fighter-jet control panels. Sensors embedded in the undergarments recorded their postures and movements every half-second, 24 hours a day, for 10 days.

The volunteers went about their normal lives, except that they ate all their meals at a Rochester hospital, scraping up every speck to leave no calorie behind.

In the next phase, the researchers fed the lean volunteers an extra 1,000 calories a day for 10 more days so they would put on pounds. The obese volunteers' meals were cut by 1,000 calories a day so they would shed weight.

Some 150 million lines of data were collected. Levine said it's the first time so much hard data has been compiled to show the different activity levels between lean and overweight people.

Based on the data, the researchers determined that each day, the lean subjects spent at least 150 more minutes moving in some way than the obese subjects.

As society and technology have made it easier for sitters to sit and harder for them to move, that inclination has been exaggerated, which could help explain a large part of the obesity problem, Levine and others said.

Mark Pereira, an obesity researcher at the University of Minnesota who wasn't involved in the Mayo study, called it a significant step in nailing down the role of nonexercise activity in obesity. He said the results from under- and overfeeding the volunteers provides good evidence that some fundamental biological characteristic is at work.

His colleague in the university's epidemiology division, David Jacobs, said it's useful to have such hard data because people typically don't have an accurate idea of how much they move or don't.

Jacobs also cautioned that there's no simple answer to the problem of obesity and that a lot of other factors contribute, including overeating. But he said other research also has shown that overweight people tend to conserve their movements.

"I guess the question is how you get a couch potato who is a nonmover to become a couch potato who's a mover," he said.