As opposed to popular beliefs, long lives may be the blessing of a few extra pounds.
According to the new research, the death rate among men and women, aged 70 to 75, is lowest for those classed as overweight.
And those pensioners classed as obese have the same risk of death as people of 'normal' weight.
However, being underweight is associated with the highest mortality.
It is thought that fat reserves could help frail older people recover from bouts of illness such as pneumonia.
Obesity is a well known risk factor for a range of fatal illnesses including cancer, heart disease, stroke and diabetes.
However, the latest study by Professor Leon Flicker suggests that losing weight once you pass 70 can dramatically increase your chances of dying.
For the study, the researchers looked at 9,240 adults, aged 70 to 75.
They found that those overweight were 13 per cent less likely to die from any cause over a 10-year period, compared with those of normal weight.
Those underweight were 76 per cent more likely to die, while obese elderly people had the same mortality risk as those of normal weight.
"This study has demonstrated that, for people who have survived to the age of 70, the risk of death is lowest among those with a BMI [body mass index] classified as overweight," the Daily Express quoted Professor Flicker as saying.
"Those in their seventies who were classified as normal weight had a higher risk of death than the overweight group," Professor Flicker added.
The link between weight and mortality applied to the most common causes of death.
"Even after removing the effects of early mortality, those who were overweight were still at lowest risk.
This is a finding consistent with the observation that weight loss in older age groups is associated with greater incidence of death," Professor Flicker said.
He admitted it was not clear why excess weight appeared to protect the elderly from death.
"We can only hypothesise, but it may be that, as we age, the presence of nutritional and metabolic reserves - ie fat - are advantageous," he said.
The research is to be published in the Journal of the American Geriatrics Society.