American Waistlines Are Still Expanding, Study Finds

American adult waistlines are still spreading, a new study finds. While body mass index, a key measure for obesity, has stabilized, American bellies have increased an inch over the last decade — to a circumference of almost 39 inches. That's bad news, researchers say.

“[Waist circumference] has kind of been picking up year after year [while] BMI flat-lined a little bit,” says Dr. Earl Ford, a medical officer at the Centers for Disease Control, and an author of a recent report published in the Journal of the American Medical Association.

CDC researchers looked at 32,816 people older than 20 from 1999 until 2011-2012, using National Health and Nutrition Examination Survey (NHANES) data to assess weight. Average age was 45. During this time, waist circumference increased from 37.6 inches in 1999-2000 to 38.8 inches in 2011-2012. Overall women’s waists increased by 1.5 inches to an average of 37.8 inches. African-American waists increased by 1.6 inches to 39 inches, while Mexican-Americans saw an increase of 1.8 inches to 39.6 inches.

Abdominal obesity is defined as a waist circumference greater than 40.2 inches in men and greater than 34.6 inches in women.

It's unclear why waistlines are still expanding while BMI hasn't changed.