WASHINGTON — Loosen the belt buckle another notch: Obesity rates continued to climb in 31 states last year, and no state showed a decline.

Mississippi became the first state to crack the 30 percent barrier for adults considered to be obese. West Virginia and Alabama were just behind, according to the Trust for America’s Health, a research group that focuses on disease prevention.

Colorado continued its reign as the leanest state in the nation with an obesity rate projected at 17.6 percent.

This year’s report, for the first time, looked at rates of overweight children ages 10 to 17. The District of Columbia had the highest percentage — 22.8 percent. Utah had the lowest — 8.5 percent.

Health officials say the latest state rankings provide evidence that the nation has a public health crisis on its hands.

Unfortunately, we’re treating it like a mere inconvenience instead of the emergency that it is,” said Dr. James Marks, senior vice president at the Robert Wood Johnson Foundation, a philanthropy devoted to improving health care.

Officials at the Trust for America’s Health want the government to play a larger role in preventing obesity. People who are overweight are at an increased risk for diabetes, heart problems and other chronic diseases that contribute to greater health care costs.

“It’s one of those issues where everyone believes this is an epidemic, but it’s not getting the level of political and policymaker attention that it ought to,” said Jeffrey Levi, the organization’s executive director. “As every candidate for president talks about health care reform and controlling health care cost costs, if we don’t home in on this issue, none of their proposals are going to be affordable.”

At the same time, many believe weight is a personal choice and responsibility. Levi doesn’t dispute that notion, but he said society can help people make good choices.

“If we want kids to eat healthier food, we have to invest the money for school nutrition programs so that school lunches are healthier,” he said. “If we want people to be more physically active, then there have to be safe places to be active. That’s not just a class issue. We’ve designed suburban communities where there are no sidewalks for anybody to go out and take a walk.”

To measure obesity rates, Trust for America’s Health compares data from 2003-2005 with 2004-2006. It combines information from three years to improve the accuracy of projections. The data come from a survey of height and weight taken over the telephone. Because the information comes from a personal estimate, some believe it is conservative.

Indeed, the Centers for Disease Control and Prevention released a study last year noting a national obesity rate of about 32 percent — a higher rate than was cited for any of the states in the Trust for America’s Health report. The CDC’s estimate came from weighing people rather than relying on telephone interviews, officials explained.

Generally, anyone with a body mass index greater than 30 is considered obese. The index is a ratio that takes into account height and weight. The overweight range is 25 to 29.9. Normal is 18.5 to 24.9. People with a large amount of lean muscle mass, such as athletes, can show a large body mass index without having an unhealthy level of fat.

A lack of exercise is a huge factor in obesity rates. The Centers for Disease Control and Prevention found last year that more than 22 percent of Americans did not engage in any physical activity in the past month. The percentage is greater than 30 percent in four states: Mississippi, Louisiana, Kentucky and Tennessee.

Meanwhile, Minnesotans led the way when it came to exercise. An estimated 15.4 percent of the state’s residents did not engage an any physical exercise — the best rate in the nation. Still, the state ranked 28th overall when it came to the percentage of obese adults.

Another factor in obesity rates is poverty. The five poorest states were all in the top 10 when it came to obesity rates. An exception to that rule was the District of Columbia and New Mexico. Both had high poverty rates, but also one of the lower obesity rates among adults.

Poverty can lead to less safe neighborhoods, which deter children from playing. It can lead to fewer grocery stores offering fruits and vegetables, and it can lead to greater reliance on fast food, officials said.

“It seems the cheapest foods are the worst ones for you,” Marks said.

Officials said the report is not designed to stigmatize states with high obesity rates but to stir them into action.

“These are the states where the urgency is the greatest. They need not to wait for others to lead. They need to become the leaders,” Marks said. “It’s the only way that they can restore the health of their children and their families. It’s the only way that they can improve their economic competitiveness.”

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On the Net:

Trust for America’s Health: http://healthyamericans.org