Researchers from the U.S. Center for Disease Control and Prevention in Atlanta, Georgia found Americans who were overweight were less likely to die of heart disease and cancers - including those commonly associated with excess weight, such as breast, kidney, pancreatic and colon cancer.
The study's lead author, Katherine Flegal, is a senior scientist at the CDC.
".... what we found is that overweight was associated with a significantly reduced number of deaths from those causes," Dr. Flegal said.
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.
The study 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.
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.
Most surprisingly, those merely overweight were up to about 40 percent less likely than normal-weight people to die from several other causes, including emphysema, pneumonia, Alzheimer's, injuries and various infections.
Flegal said research has suggested that extra heft might supply the body with vital reserves to draw upon to fight illness and aid recovery.
"You may not just have more fat. You may also have more lean mass - more bone and muscle," Flegal said. "If you are in an adverse situation, that could be good for you."
The World Health Organization says about 400 million individuals around the globe are grossly overweight
Dr. Flegal notes that while their overall chance of dying of cancer at first does not appear to be increased, things changed when they divided cancer into sub-groups, including a group of cancers that are considered to be obesity-related, like colon cancer, breast cancer, pancreatic cancer, kidney cancer, and some others.
And they found that about 11 percent of deaths from those cancers were associated with obesity.
Dr. Flegal stresses people should not interpret the findings - that extra kilos may be protective against cancer and heart disease - as license to maintain an unhealthy lifestyle.
"I would like to emphasize that our study does not change the basic public health recommendations," Dr. Flegal said. "You should eat right, get some activity, and do not smoke. Nothing about our study changes those recommendations."
Yet to be determined is why people who are above their ideal weight appear not to be at increased risk of dying of cancer and heart disease.
American Heart Association spokesman Robert Eckel told the Associated Press,
... 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 aren't always deadly, he said.