A year ago, Dr. James Hill took a deliberate step to change fat America: Every day, he declared, people should walk a little more and eat a little less to prevent weight gain.

It’s a deceptively simple strategy to attack a huge and complex problem. Being overweight contributes to several killer diseases, especially cardiovascular disease and cancer. Two out of every three people are too heavy, and kids are growing extra-large at a rate even faster than their flabby parents.

It was a risky step, too. Hill and his colleagues launched an initiative called America on the Move with great fanfare but not much scientific data.

Now some early results are trickling in. While far from conclusive, these initial studies support Hill’s idea that walking as little as 2,000 more steps a day and eating 100 fewer calories will create some good habits to prevent weight gain. With more exercise, many participants report they begin to lose weight, too.

Meanwhile, America on the Move has spread from its Colorado origins to chapters in 20 states with more than 300,000 registered participants. The nonprofit program also is gathering some big-name corporate and medical partners, including the Mayo Clinic and American Academy of Family Physicians.

It’s an example of how hungry people are for an easy solution to the nation’s fastest-growing health issue.

“You can’t just tell people to triple their physical activity overnight,” said Hill, who is aiming for 1 million participants. “You have to make small changes or they will fail.”

Hill published his first research paper in the Journal of Physical Review and Health, a small quarterly launched in January by leading researchers in obesity and exercise science.

The study used pedometers to track physical activity over a 14-week period of 298 people at their jobs and more than 100 worshippers at churches in Denver.

In both groups, about half of the people who reported their daily activity increased their steps by 2,000 or more steps, which translates to burning 80 to 100 extra calories.

The study’s initial phase did not measure participants’ weight gain or loss. Nor did it include a control group with people who did not take part in the pedometer program. That will come later.

Also, many participants did not consistently track and report their walking during the 14-week period, leading to data gaps.

Hill acknowledged the shortcomings and described the slow pace of the research as frustrating. Still, he said, the preliminary results show that people will stick to regular physical activity programs that are not too ambitious.

For example, last year the Centers for Disease Control and Prevention recommended that people walk 10,000 steps a day, or about five miles.

Hill calls that goal “unattainable” considering that most Americans regularly walk a fraction of that distance. Even in Colorado, the nation’s leanest state, the average person walks fewer than 3,000 steps per day. Obesity rates here have more than doubled since 1990.

“Government hasn’t moved the needle on this issue,” said Hill, who is director of the Center for Human Nutrition at the University of Colorado Health Sciences Center in Denver. “Using this small change method, we can increase total physical activity.”

Other researchers believe obesity has more to do with an individual’s metabolism, as well as the body’s ingrained tendency since prehistoric times to survive famine by storing fat and conserving energy. Many experiments are trying to find drugs to effectively curb the body’s natural inclinations or even genetic alterations to change metabolism.

“When it comes to quitting smoking, we’ve got tons of resources and we agree on the strategy,” Hill said. “But with obesity, we’re still arguing about what to do.”

Even without mountains of data, groups nationwide are embracing the low-tech walking initiative. A national online “pledge” day for people to try walking more and eating less is scheduled for Nov. 5.

In Indiana, 2,000 members of the state extension homemakers association, a group that provides continuing education and community service projects, joined the program in May.

The University of Tennessee plans to subsidize the cost of pedometers for Knoxville campus employees and is promoting the program during halftime on its televised football games. And in a friendly challenge between the state’s two senators, Lamar Alexander’s staff walked a total of 5.3 million steps to the 4.1 million steps tallied by the staff of Senate Majority Leader Bill Frist, a heart surgeon.

In Saratoga Springs, N.Y., Mayor Mike Lenz has lost 10 pounds walking 3,000 extra steps every morning. The American Society of Family Physicians is collaborating with America on the Move in a program called Americans in Motion to launch walking programs for the office staffs of its 93,000 members. If it succeeds, recommendations for their overweight patients would follow.

In Denver, the pharmacy in the city’s central public hospital is stocking pedometers so that physicians can prescribe them, reducing the cost for insured patients.

In Rochester, Minn., Hill’s team is creating a worksite walking program at the Mayo Clinic headquarters this fall.

Not everyone has joined. The program contacted McDonald’s, which instead launched its own “Go Active” salad meals with a pedometer and exercise booklet last May.

Blue Cross and Blue Shield, the largest health insurance network, established WalkingWorks, urging 89 million subscribers to wear pedometers and take a brisk walk every day. It suggests adding 500 steps every two weeks until you are walking 10,000 steps.