ANN ARBOR, Mich. — Preston Brooks replaced lunchtime bacon double-cheeseburgers with submarine sandwiches loaded with vegetables.

And never looked back.

The 12-year-old sixth-grader credits his healthier outlook to an ambitious effort in five middle schools to tackle obesity.

"I've learned how to make better choices about what I eat," Brooks said.

So have more than 1,000 other students. Since the Healthy Schools program began as a pilot program at one middle school three years ago, sixth-graders who have taken part in it have lost weight and lowered their blood pressure and cholesterol levels.

The project uses 20-minute lessons, motivational speakers and eye-catching props to teach kids about basic nutrition and encourage exercise. The program is a collaboration between Ann Arbor public schools and the University of Michigan Health System.

The 12-week program, which includes medical screenings OK'd by parents, now is offered at all five Ann Arbor middle schools. About 1,200 sixth-graders are signed up, and about half of those are part of an ongoing study that's tracking results and lifestyle changes.

Early survey results are promising.

Forty percent of those studied last year were considered "at-risk" in at least one medical screening category. Thirty-two percent were overweight, 9 percent had high blood pressure and nearly 10 percent had cholesterol levels above 200, a troubling sign at such an early age.

Those numbers belied Ann Arbor's well-educated, health-conscious image, where the University of Michigan casts a long shadow and many children come from white-collar homes. The results also affirmed a long-standing belief held by the program's lead organizer.

"We know child obesity is an epidemic, but we never want to believe it's a problem locally," said Dr. Kim Eagle, a University of Michigan cardiologist who helped raise $100,000 in donations and public grants to launch the project in 2004.

By last spring, students who were being tracked in the program showed improvement in every medical screening category.

Of the 292 students who took part in the study of 2005-06, 47 of 142 with high triglycerides reduced their levels. Nine of the 21 students who had cholesterol levels above 200 reduced them below that mark. Researchers didn't make numbers available on the students who lost weight but noted that several did.

So, how did Ann Arbor do it?

Organizers followed this simple lesson plan: Teach good eating habits, promote fitness and nudge school administrators into offering healthier foods.