The trend could be a result of improved lifestyle and treatment of heart disease, the authors said. Heart disease is one of the main causes of death associated with obesity.
Paul F. Campos, a University of Colorado law professor and author who believed obesity has been overstated as a health risk, said the new study called for a reevaluation of the relationship between weight and health.
He pointed to the study's finding that overweight people -- those with a BMI between 25 and 29.9 -- had fewer deaths than people in the healthy weight range.
"I think this is just a bombshell," Campos said. "The real undeniable fact is the entire overweight definition ... is a completely spurious definition."
Stanton Glantz, professor of medicine at UC San Francisco, said the new numbers showed obesity was nowhere near as serious a health concern as tobacco.
Obesity "is presented as a crisis and it's presented as this horrible problem which has exploded onto the scene," Glantz said. "What this paper shows is that it's just not true."
But some scientists said the study was flawed.
One of the main problems, Harvard's Willett said, is that he did not believe it adequately controlled for smokers and the sick. Because those people tend to be thinner -- for unhealthy reasons -- they could make the healthy weight category appear to have a much higher death rate.
In studies that remove smokers and the sick, overweight people are clearly at higher risk for disease and death, Willett said.
The authors said that they did remove smokers and some other high-risk groups from their study, with no significant difference in results.
The authors and other scientists cautioned that the study did not mean that being overweight or obese was harmless.
Carrying extra fat is associated with an increased risk for diabetes, heart disease and certain cancers, which cause complications, medical costs and an eroded quality of life.
"Overweight is associated with other factors than just mortality," Flegal said. "There's quality-of-life issues.... I think we couldn't use our data to really make a statement that overweight is benign."
The study builds on a controversy that has been roiling since an earlier estimate of 400,000 annual obesity deaths was published last March. (That number was reduced to 365,000 in January after the scientists found an error.)
The paper, written by four CDC scientists including the center's head, Dr. Julie L. Gerberding, was heralded with much fanfare. Its publication coincided with the unveiling of a new government anti-obesity campaign.
It was later revealed that some CDC scientists had objected to the paper's methodology before its publication, and the matter eventually led to an internal investigation at the CDC.
