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A big network of walking and cycling paths, wide sidewalks and, most of all, plenty of parks make Washington D.C. the nation’s fittest city, according to the American College of Sports Medicine.

And despite its notoriously snowy weather, Minneapolis-St. Paul ranks second on the fitness index issued annually by the group. Last place goes to Indianapolis, with Memphis scoring barely any better.

The secret? Making healthy living easy, experts agree.

"If I want to be physically active, if I want to maintain my healthy lifestyle, does my community or the environment support that?”

“If you walk out onto the (National Mall) at noon, tourists can't get around because there are so many people exercising, so many people walking and jogging. And on the weekend they are playing kickball on the Mall,” said Walt Thompson of Georgia State University, board chair for the report.

The American College of Sports Medicine and the Anthem Foundation put together the fitness index using data on smoking, exercise, rates of asthma and heart disease.

“But what makes the American Fitness Index really unique is that we combine these personal health indicators with what we call community or environmental indicators,” Thompson told NBC News.

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“Basically it answers the question: If I want to be physically active, if I want to maintain my healthy lifestyle, does my community or the environment support that?”

Last year, Minneapolis was No. 1 in the index. What makes a city a winner, says Thompson, is a combination of opportunities to exercise and access to healthful foods.

“The parks are accessible in Washington, D.C."

“The parks are accessible in Washington, D.C.,” Thompson said. “The second interesting thing about Washington is how much money they spend per person per capita on parks: $287 per capita for every single person who lives in Washington, DC. Now in comparison, the lowest city on the American fitness index, Indianapolis, spends about $27 per capita on their parks.”

Healthy eating isn’t so popular in the lower-ranked cities, Thompson said. “Folks in Indianapolis, like folks in the Southeast where I live, we love to eat and unfortunately we don't eat enough fresh fruits and vegetables,” Thompson said.

At least two-thirds of Americans are overweight or obese, and have skyrocketing levels of heart disease, diabetes and other obesity-related diseases, including certain cancers.

And recent studies show nearly 30 percent of the global population, or 2.1 billion people, are either overweight or obese. Not a single country has lowered its obesity rate since 1980, And even though the United States accounts for just 5 percent of the world’s total population, Americans make up 13 percent of the global overweight and obese population.

New dietary guidelines coming out for Americans aim to get people to eat more vegetables, less fat and salt and to exercise more. The U.S. Institute of Medicine recommends that Americans get at least 60 minutes a day of moderate exercise, such as brisk walking.

But the ACSM/Anthem survey found an 11 percent decrease in the number of people who exercise regularly. “We're not exactly sure why that’s happening, except there are some things in cities that are happening that aren't making them safe any longer to exercise,” Thompson said.

Here’s how some U.S. cities rank:

Top 10

Washington, D.C. Minneapolis/St. Paul San Diego San Francisco Sacramento Denver Portland Seattle Boston San Jose

Bottom 10