CHICAGO – Being overweight is nowhere near as big a killer as the government thought, ranking no. 7 instead of no. 2 among the nation’s leading preventable causes of death, according to a startling new calculation from the CDC.

The Centers for Disease Control and Prevention estimated yesterday that packing on too many pounds accounts for 25,814 deaths a year in America. As recently as January, the CDC came up with an estimate 14 times higher: 365,000 deaths.

The new analysis found that obesity – being extremely overweight – is indisputably lethal. But like several recent smaller studies, it found that people who are modestly overweight actually have a lower risk of death than those of normal weight.

Biostatistician Mary Grace Kovar, a consultant for the University of Chicago’s National Opinion Research Center in Washington, said “normal” may be set too low for today’s population. Also, Americans classified as overweight are eating better, exercising more, and managing their blood pressure better than they used to, she said.

The study – an analysis of mortality rates and body-mass index, or BMI – was published in the Journal of the American Medical Association. Based on the new calculation, excess weight would drop from the second leading cause of preventable death, after smoking, to seventh. It would fall behind car crashes and guns on the list of killers.

Calculating the health effects of obesity has been a major source of controversy at the CDC.

Last year, the CDC issued a study that said being overweight causes 400,000 deaths a year and would soon overtake tobacco as the top American killer. After scientists inside and outside the agency questioned the figure, the CDC admitted making a calculation error and lowered its estimate three months ago to 365,000.

CDC Director Dr. Julie Gerberding said because of the uncertainty in calculating the health effects of being overweight, the CDC is not going to use the brand-new figure of 25,814 in its public awareness campaigns and is not going to scale back its fight against obesity.

“There’s absolutely no question that obesity is a major public health concern of this country,” she said. Dr. Gerberding said the CDC will work to improve methods for calculating the consequences of obesity. Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women’s Hospital in Boston, said she is not convinced the new estimate is right.

“I think it’s likely there has been a weakening of the mortality effect due to improved treatments for obesity,” she said. “But I think this magnitude is surprising and requires corroboration.”