A new study shows that older women find it more difficult to stay fit than older men because they lose part of their ability to store protein as muscle, as they age.
The researchers from the University of Nottingham in the UK and Washington University School of Medicine in the US, studied 29 men and women aged between 65 and 80. They found that because of the differing ways in which male and female bodies metabolized food, older women did not use protein effectively to maintain muscle.
The male body seemed to be able to store protein in the muscle and use this to make them stronger.
According to the research team that published the findings in the journal PLoS One, this difference between the sexes could be triggered by the reduction in the hormone estrogen for women, during the menopause.
It has been observed that in the case of men, levels of estrogen remain high, well into old age.
Estrogen is known to help men and women retain bone density and may perform a similar role in the preservation of muscle.
"Nobody has ever discovered any mechanistic differences between men and women in muscle loss before," said Michael Rennie, professor of clinical physiology at the University of Nottingham.
"This is a significant finding for the maintenance of better health in old age and reducing demands on the National Health Service. Rather than eating more, older people should focus on eating a higher proportion of protein in their everyday diet," he added.
Health experts suggest eating protein-rich foods such as eggs, fish, chicken and lean red meat and regular "resistance exercise" such as weightlifting, as tips for building muscle.
"We know that women tend to have less muscle bulk than men as they enter old age so the advice to eat more protein is very sensible indeed," said British Dietetic Association spokesman Jackie Lowdon.
Lowdon added, "Many elderly people subsist on toast and biscuits - food that is easy to make - and there needs to be a much greater focus than there is at present on improving the diets of those who are already vulnerable."
People lose up to 0.4% of muscle mass every year from the age of 50 onwards. This makes them less mobile and increases the risk of a life-threatening fall.
Statistics show that currently, half of all elderly people who suffer a serious fall die within two years.