DURHAM, N.C. — Today, just over a third of U.S. adults are obese, but by 2030 that figure will be 42%, according to a forecast released May 7 by researchers at the Centers for Disease Control and Prevention, Duke University and RTI International. Somewhat encouraging is the fact that earlier forecasts based on unabated increases in obesity put the number of obese adults in 2030 at about 51%. The researchers noted evidence now suggests that obesity prevalence may be leveling off.

The number of individuals with severe obesity, which is defined as a body mass index over 40 or roughly 100 lbs overweight, was forecast at 11%, up from about 5% currently.

The goal, researchers said, is to keep obesity levels from increasing. If the United States is able to keep obesity at 2010 levels, the combined savings in medical expenditures over the next two decades would be nearly $550 million, the researchers said.

“We know more than ever about the most successful strategies that will help Americans live healthier, more active lives and reduce obesity rates and medical costs,” said William H. Dietz, M.D., Ph.D., director of the C.D.C.’s Division of Nutrition, Physical Activity and Obesity. “People need to make healthy choices, but the healthy choices must first be available and accessible in order to make them.”

The findings were part of a study based on data from the Behavioral Risk Factor Surveillance System and state-level data from the Bureau of Labor Statistics and other organizations. They were published in the American Journal of Preventive Medicine on May 7.