Wednesday March 26 2008
Research has shown that “women find it harder than men to keep in shape as they get older,” the Daily Mail reports today. It says that women should eat lots of protein to try to compensate for the muscle that they lose during the aging process. Older men, however, have no problems in converting the protein that they eat into muscle.
The report is based on an experiment carried out in 29 elderly people. The researchers examined the effects of food on the production of muscle proteins. Contrary to what might be concluded from reading the report, although women tend to have less muscle than men, they lose this muscle at a slower rate when they age. This study suggests that this might be because women have a higher, more consistent basic rate of muscle protein synthesis (MPS) throughout the day, rather than just after eating. However, as the study only had a small number of participants, it is not possible to make any robust conclusions about muscle differences between elderly men and women without further research.
This study did not address the effects of eating a higher proportion of protein or increasing resistance exercise on MPS. Therefore, it does not affect current advice regarding diet and exercise in an elderly population.
Where did the story come from?
Gordon Smith and colleagues from the School of Medicine, Washington University, USA and the School of Graduate Entry Medicine and Health, University of Nottingham, UK carried out the research. The study was funded by the US National Institutes of Health, the University of Nottingham, the UK Biotechnology and Biological Sciences Research Council and a European Union grant. It was published in PloS One, an open-access, peer-reviewed online scientific journal.
What kind of scientific study was this?
This experimental study was designed to investigate how muscle is lost with aging in men and women. The researchers suspected that the differences in MPS between the sexes might play a role. This was investigated by measuring MPS during and after the participants were fed.
The researchers recruited 13 men and 16 women between the ages of 65 and 80 who were matched for age and body mass index. All subjects were healthy non-smokers who didn’t drink excessively, but who also did not exercise regularly. Some were being treated for high cholesterol and high blood pressure.
As part of the study, the subjects were admitted to the research centre and given a balanced evening meal. The next morning, a blood sample and muscle biopsy was taken which measured the concentrations of sex hormones, inflammatory markers, the amino acid leucine in muscle (amino acids are the building blocks of protein) and total muscle RNA (the product of gene activity). For the next six hours, the participants were given an infusion of a solution of leucine (tagged with radioactivity so that it could be traced within the body). Three and half hours after the infusion began, a second muscle biopsy was taken to determine the rate of MPS and the concentrations of certain proteins involved in this process. A balanced liquid meal was then given to each of the subjects. A further muscle biopsy was taken 2.5 hours after this to look at the rate of MPS and responses to feeding.
During the entire study, blood samples were taken every 30 minutes to look at leucine, glucose and plasma concentrations in the blood. The researchers used statistical analyses to look at whether there was a difference between men and women in glucose, insulin, leucine, muscle protein and muscle RNA expression.
What were the results of the study?
The researchers found that, at the start of the study, total fat free mass, muscle mass and leg muscle volume were 25% lower in women than in men. The women had significantly lower blood testosterone levels than the men, but there was no difference in oestrogen and progesterone levels between the sexes. After being fed, the concentration of both insulin and glucose concentration increased equally in men and women.
The rate of MPS before the liquid meal was about 30% higher in men than women. However, having the liquid meal increased the rate of MPS in men but not in women.
What interpretations did the researchers draw from these results?
The researchers conclude that there is a difference in MPS between older men and women. They also say that the greater base rate of MPS in women may explain why they lose muscle mass more slowly than men as they age.
What does the NHS Knowledge Service make of this study?
This study gives some indication of the differences between men and women in MPS, both before and after eating. However, its small size means that we cannot be certain that these differences are representative of what happens in all elderly men and women. The study also has some other limitations, which the authors acknowledge. For example, they did not assess the rate of muscle protein breakdown and it is therefore not possible to say whether there is a difference between men and women in the rates at which they produce and breakdown proteins.
The researchers also only measured pre-feeding MPS at one time point in each person. It is, therefore, not clear whether the higher rate of MPS in women is maintained throughout the day.
This study did not address the effects of eating a higher proportion of protein or increasing resistance exercise on MPS, so it does not affect current advice regarding diet and exercise in an elderly population.
Sir Muir Gray adds...
As an older person in poor shape, I rely on exercise to keep the effects of modern lifestyle at bay. Five minutes of stretching and strength exercises every morning before walking to the bus stop - part of my 3000 extra vital steps a day - is my recipe.