A few extra pounds might help you live longer if you’re past your prime but otherwise healthy, a new study finds.

“Perhaps we should tell our grandparents to get fat,” chuckled geriatrician Dr. Thomas Yoshikawa, “to go ahead and eat that candy.”

Although his suggestion may seem counterintuitive, Yoshikawa is only half-joking. The Journal of The American Geriatrics Society, of which he is editor-in-chief, just published a report showing that overweight elderly Australians were 13 percent less likely to die during a 10-year period than those who kept their weight within the recommended range.

Physicians routinely follow guidelines issued by the World Health Organization when they advise patients about their waistline. Because weight depends on height, they use a standard measure called body mass index (BMI), which is calculated as the weight in kilograms divided by the height in meters squared.

Healthy weight is defined as a BMI anywhere between 18.5 and 24.9 in adults, whereas 25 to 29.9 is overweight and 30+ is obese.

The new study suggests that in the elderly, these boundaries may be too narrow. While no one is questioning that extra fat poses health risks in young and middle-aged adults, it may cushion the impact of frailty and old age, Yoshikawa told Reuters Health.

“We’re not advocating that people get obese,” said Yoshikawa, who was not involved in the new study. But “if you are five or 10 pounds heavier, it’s better than being five or 10 pounds lighter.”

So far, nobody knows exactly how BMI affects lifespan in older people. Some researchers speculate that it acts as an energy reserve that can help the elderly cope with illness.

For the study, Australian researchers followed more than 9,000 men and women who were between 70 and 75 years old at the outset. The participants reported their height and weight as well as various factors related to health and lifestyle. About 33 percent of the women and 44 percent of the men were overweight.

Over 10 years, more than 2,000 of the participants died. Women who had an active life and didn’t smoke were the most likely to be alive at the end of the study.

But neither health nor lifestyle could fully explain why overweight people of both sexes survived longer than their normal-weight peers, who fared no better than obese individuals. In terms of survival, the best BMI was between 26 and 27, well within the overweight range.

“We did find it surprising,” Dr. Leon Flicker, the study’s lead researcher, told Reuters Health in an e-mail.

The new results are consistent with earlier research showing that fat may be beneficial in old age. But Flicker, who directs the Western Australian Centre for Health & Ageing at the University of Western Australia, said he had not expected a decidedly protective effect.

While the findings are based on people living in the community and may not apply to sick or frail people in nursing homes, Flicker still believes physicians should bear them in mind when seeing patients.

“If somebody is over the age of 70 years, and does not have a specific problem associated with being overweight (such as diabetes mellitus or severe osteoarthritis) then there is no need to provide advice to lose weight,” he said.

Other experts urge caution before changing medical recommendations. So far, they say, studies have never directly tested the effect of gaining weight in old age.

“There is no evidence to suggest that intentionally gaining weight is good,” Ian Janssen, an epidemiologist at Queen’s University in Canada who was not part of the new research, told Reuters Health. Factors such as high blood pressure and daily function need to be taken into account, he added.

Still, Yoshikawa noted, if you are healthy and fit once you reach 70, you probably don’t have to worry about a little extra fat, because the negative health consequences usually don’t kick in for several years.

SOURCE: Journal of the American Geriatrics Society, February 2010.