'We really can't afford to become complacent about this epidemic of obesity and certainly not based on findings from [a flawed] analysis,' said Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston.

Health experts increasingly are faulting a recent study by scientists at the federal Centers for Disease Control and Prevention that concluded obesity is not nearly as dangerous as was thought and that being a little plump might actually lower the risk of death.

At a news conference, CDC chief Dr. Julie Gerberding acknowledged potential flaws in the study and pledged to get scientists and the public back on track.

"It is not OK to be overweight. People need to be fit, they need to have a healthy diet, they need to exercise," she said. "I'm very sorry for the confusion that these scientific discussions have had."

Obesity raises the risk of heart disease, some cancers, diabetes and arthritis -- and being overweight raises blood pressure and cholesterol, which in turn raise the risk of heart disease, she noted.

'Thin Because They're Sick'

The disputed report, published in April, said obesity accounts for a mere 25,814 deaths a year in the United States, vastly lower than the 365,000 deaths estimated just months earlier. Mildly overweight people had a 20 percent lower risk of dying than those who weigh less, it also found.

Many scientists from the Harvard School of Public Health, the American Heart Association and the American Cancer Society now reject those conclusions. They say the study's main flaw is that it included people with health problems ranging from cancer to heart disease, who tend to weigh less because of those problems and therefore make pudgy people look healthy by comparison.

Doing this is "looking at people who are thin because they're sick, not who got sick because they're thin," said Dr. Michael Thun, the cancer society's chief epidemiologist.

"If you want to define optimal weight for healthy people, you need to start with healthy people," agreed Dr. Meir Stampfer, chief of epidemiology at Harvard School of Public Health.

Gerberding acknowledged the controversy over this point and said people need to look at the overall evidence of harm from excess pounds.

"It's not healthy to be overweight," she said.

Big-Picture Message

Two other signs suggested the CDC was backing off the report. Its Web site now says the study "estimates that obesity is related to about 112,000 deaths." In fact, the study started with that number and then subtracted the benefits of being modestly overweight, arriving at the 25,814 figure.

The study's author, Katherine Flegal, also was not at the Thursday news conference. Instead, Gerberding and Donna Stroup -- authors of the previous study setting obesity-related deaths much higher -- did the talking.

Afterward, the Center for Consumer Freedom, a group with ties to the restaurant and food industry, repeated its claim that CDC has knowingly misled the public about the scope of the obesity problem.

However, scientists said they were relieved that CDC was returning to the big-picture message, that obesity is a serious and growing health problem.

"This issue is far too important to be trivialized over methodological disagreements," Thun said.

"We really can't afford to become complacent about this epidemic of obesity and certainly not based on findings from an analysis" that is flawed, said Dr. JoAnn Manson, chief of preventive medicine at Brigham and Women's Hospital in Boston.

Also on Thursday, the Institute of Medicine released a report from a workshop last December that gives a roadmap for improving research on obesity and deaths.

"We are taking it seriously," Gerberding said of the report.