25 pounds (11 kilos) extra weight do not appear to raise your risk of dying from cancer or heart disease.
Released just a few weeks before the Thanksgiving holiday when Americans typically overeat, the findings might comfort some who cannot seem to lose those last 15 pounds (6.8 kilograms). And they hearten proponents of a theory that it is possible to be "fit and fat."
The news is not all good: Overweight people do have a higher chance of dying from diabetes and kidney disease.
And people who are obese - generally those more than 30 pounds (13.6 kilograms) overweight for their height - have a higher risk of death from a variety of ills, including some cancers and heart disease.
However, having a little extra weight actually seemed to help people survive some illnesses - results that baffled several leading health researchers.
"This is a very puzzling disconnect," said Dr. JoAnn Manson, chief of preventive medicine at Harvard's Brigham and Women's Hospital. "That is a conundrum."
It was the second study by the same government scientists who two years ago first suggested that deaths from being too fat were overstated.
The new report further analyzed the same data, this time looking at specific causes of death along with new mortality figures from 2004 for 2.3 million U.S. adults.
"Excess weight does not uniformly increase the risk of mortality from any and every cause, but only from certain causes," said the study's lead author Katherine Flegal, of the U.S. Centers for Disease Control and Prevention.
The study, which appears in Wednesday's Journal of the American Medical Association, analyzed the body-mass index of people who died from various diseases.
In many cases, the risks of death were substantial for obese people - those with a body-mass index, or BMI, of at least 30.
Specifically, obesity raised the risk of death from heart disease, diabetes and kidney disease, and several cancers previously linked with excess weight, including breast, colon and pancreatic cancer.
But being merely overweight - having a BMI between 25 and 30 - did not increase the risk of dying from heart disease or any kind of cancer.
Also surprising was that overweight people were up to about 40 percent less likely than normal-weight people to die from several other causes including emphysema, pneumonia, injuries and various infections. The age group that seemed to benefit most from a little extra padding were people aged 25 to 59; older overweight people had reduced risks for these diseases, too.
Why extra fat is not always deadly and might even help people survive some illnesses is unclear and in fact disputed by many health experts.
But University of South Carolina obesity researcher Steven Blair, who says people can be fat and fit, is a believer. He called the report a careful and plausible analysis, and said Americans have been whipped into a "near hysteria" by hype over the U.S.'s obesity epidemic.
While the epidemic is real, the number of deaths attributed to it and to being overweight has been exaggerated, Blair said.
People should focus instead on healthful eating and exercise, and stop obsessing about carrying a few extra pounds or becoming supermodel thin, Blair said.
He says his hefty grandmother used to justify her extra padding, saying, '"That way I have protection in case I get sick.' Maybe there is something to that."
A little extra weight might provide "additional nutritional reserves" that could help people battle certain diseases, Flegal said.
Dr. Robert Eckel, a spokesman for the American Heart Association, argued that the results may be misleading. For example, diabetes and heart disease often occur together and both often afflict overweight people. So when diabetes is listed as a cause of death, heart disease could have contributed, he said.
Eckel also said the study results might reflect aggressive efforts to treat high blood pressure and cholesterol or other conditions that can lead to fatal heart attacks. Those conditions often occur in overweight people and can be costly and debilitating even if they are not always deadly, he said.
Obesity researcher Barry Popkin of the University of North Carolina in Chapel Hill, agreed, noting that the study "is about death. This is not about health and sickness."
It does not address whether cancer and heart disease occur more often in overweight people - something that has been suggested by other research.
Dr. Michael Thun of the American Cancer Society noted that staying slim tops a recent list of recommendations for preventing cancer in a report from the World Cancer Research Fund and American Institute for Cancer Research. The report was based on a review of more than 7,000 studies.
The CDC report "definitely won't be the last word," Thun said.
Manson, the Harvard researcher, cautioned that extra pounds can lead to obesity so people should not be complacent about being overweight.