ATLANTA – The South tips the scales again as the nation’s fattest region, according to a new government survey.

More than 30 percent of adults in Mississippi, Alabama and Tennessee are considered obese. In part, experts blame Southern eating habits, poverty and demographic groups that have higher obesity rates.

Colorado was the least obese, with about 19 percent fitting that category in a random telephone survey done last year by the Centers for Disease Control and Prevention.

The 2007 findings are similar to results from the same survey the three previous years. Mississippi has had the highest obesity rate every year since 2004. But Alabama, Tennessee, West Virginia and Louisiana have also clustered near the top of the list, often so close that the difference between their rates and Mississippi’s may not be statistically significant.

The South has had high death rates from heart disease and stroke, health risks that have been linked to obesity, some experts noted.

The CDC study only surveyed adults, but results for kids are similar, said Dr. Miriam Vos, assistant professor of pediatrics at Atlanta’s Emory School of Medicine.

“Most of the studies of obesity and children show the South has the highest rates as well,” Vos said.

Why is the South so heavy? The traditional Southern diet – high in fat and fried food – may be part of the answer, said Dr. William Dietz, who heads CDC’s nutrition, physical activity and obesity division.

The South also has a large concentration of rural residents and black women – two groups that tend to have higher obesity rates, he said.

The study found that about 36 percent of black survey participants were obese, while 28.5 percent of Hispanics and 24.5 percent of whites were.

High poverty rates in the South probably are another factor, said Naa Oyo Kwate, assistant professor of sociomedical sciences at Columbia University’s Mailman School of Public Health.

In today’s America, poor people tend to be obese: The cheapest foods tend to be calorie-heavy, and stores offering healthier, and more expensive, food choices are not often found in poor neighborhoods, she said.

And why is Colorado so thin? It’s a state with a reputation for exercise. It has plentiful biking and hiking trails, and an elevation that causes the body to labor a bit more, Dietz said.

Obesity is based on the body mass index, a calculation using height and weight. A 5-foot, 9-inch adult who weighs 203 pounds would have a BMI of 30, which is considered the threshold for obesity.

CDC officials believe the telephone survey of 350,000 adults offers conservative estimates of obesity rates, because it’s based on what respondents said about their height and weight. Men commonly overstate their height and women often lowball their weight, health experts say.

“The heavier you are, the more you underestimate your weight, probably because you don’t weigh yourself as often,” Dietz said.

Overall, about 26 percent of the respondents were obese, according to the study, published this week in CDC’s Morbidity and Mortality Weekly Report.

A different CDC survey – a gold-standard project in which researchers actually weigh and measure survey respondents – put the adult obesity rate at 34 percent in 2005 and 2006.