PORTLAND – The largest city in the state with New England’s worst obesity and chronic disease rates has emerged as a leader in the fight against fat.

Portland tied with Burlington, Vt., for the lowest rate of overweight adults nationwide, according to a 2002 survey by the Centers for Disease Control and Prevention. The rate in both cities was 49.3 percent.

In terms of obesity, Portland had the second-lowest rate, 15 percent, trailing only Denver, at 14.2 percent.

By contrast, Maine’s obesity rates hover around the national average, and about a third of the state’s kindergartners are overweight or at risk of becoming so.

Clearly, Portland must be doing something right.

Observers point to the city’s network of trails and parks, its weekly farmers market in the heart of the downtown and a population that includes a high concentration of professionals who want to live in an urban environment while having easy access to outdoor attractions.

“It’s a small enough town where you don’t have to drive everywhere,” said Sarah Cormier, a retirement plan analyst who lives in Sebago and works in Portland, where she patronizes the farmers market in Monument Square.

The market’s accessibility is one of the reasons Portland gets high marks from magazines such as Vegetarian Times and Outside. There are also wide sidewalks that encourage people to walk instead of drive.

“Well-designed cities and neighborhoods, and good health go hand in hand,” said Alan Caron, president of GrowSmart Maine, a nonprofit group that studies local growth issues.

Brent Howard, director of personal training at Bally Total Fitness, cited the willingness of employers to help pay for workers’ gym memberships in order to promote healthy habits.

Howard said he has no shortage of motivated clients, at least a third of whom are “people who came [to Portland] for the job and had inherited the lifestyle from somewhere else.”

Smaller cities are following Portland’s lead. Lewiston has been trying to get people onto its walking and biking paths along the water and to enhance its park system.

“We’re seeing more people at lunchtime walking, which is somewhat new,” said City Planner Gil Arsenault.

Caron said people are migrating to cities such as Portland and Lewiston to enjoy a sense of community and be able to walk to grocery stores and schools.

“We’re building a lot of places around that don’t even have sidewalks … and that is not where the marketplace is headed,” he said.

Morgan Downey, executive director of the American Obesity Association, said the exact reasons behind Portland’s success are difficult to pinpoint.

When Colorado and other Western states were lauded for healthful living, some speculated that residents of those states were a self-selecting group who had sought out places flush with athletic opportunities such as skiing, Downey said.

That theory was somewhat upended, Downey said, when the rate of obesity in these states started to catch up with the rest of the country.

“There’s just a lot of questions as to what’s behind the geographic variation,” Downey said.