In a review of almost 100 past studies covering nearly three million people, researchers found that being overweight or slightly obese was linked to about a 6 per cent lower risk of dying, compared to people considered "normal weight."
Being severely obese, however, was still tied to an almost 30 per cent higher risk of death.
The idea that being somewhat overweight could be linked to better health has been dubbed the obesity paradox, even though actual obesity is generally not associated with the apparent "benefit."
"This is actually the common finding," said the new study's lead author Katherine Flegal, a senior scientist from the US Centers for Disease Control and Prevention in Hyattsville, Maryland.
Her work, she said, confirms what previous analyses found - a link between being somewhat overweight and having a lower risk of death.
The paradox, as scientists have called it, is based on past findings that suggest overweight and obese people - even those with additional health problems - live longer than their thinner counterparts.
Some have argued that the pattern is a statistical one only because being thin, especially in old age, is often a sign or a result of serious illness - so the thinner people seem to have higher mortality.
The study results certainly do not give people permission to pack on extra pounds, according to Dr. Steven Heymsfield, the executive director of the Pennington Biomedical Research Center in Baton Rouge, Louisiana.
Heymsfield, who co-authored an editorial accompanying the new report, said the difference in mortality between overweight and normal weight people is probably very small.
"That's actually a very small number. It's probably only statistically significant because of the large number she had in her study," he added.
Also, there are concerns that body mass index (BMI) - a measurement of weight in relation to height - is not an accurate measure of someone's health risks.
For example, Heymsfield said a soldier may be considered overweight but still be healthy, because he or she has more muscle mass.
"It's not a good marker for body fat or health risk," he said.
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