Friday January 25 2013
Losing weight is achievable for both sexes
‘Women have to work harder than men to lose weight and get fit’ the Daily Mail says, reporting that women have to do around 20% more exercise to get the same benefits.
The Mail’s coverage on this study is arguably woeful – offering a combination of both misleading and confusing reporting.
This was an extremely small, experimental study of 10 men and 12 women with type 2 diabetes and obesity.
The participants performed handgrip tests and had their blood pressure, heart rate and other body measures taken before and after taking part in a 16-week aerobic exercise programme that involved walking four days a week outside or on a treadmill.
The main finding was that women’s blood pressure took longer to ‘recover’ (fall back to ‘normal levels’) following a handgrip test than men, both before and after the exercise programme.
The researchers suggest this is down to differences between men and women in the ‘automatic’ response of our blood vessels.
What practical implications slight variations in blood pressure levels would have on real-world health outcomes, such as diabetes, is unclear.
What we do know is that a 16-week exercise programme had no effect on the fat mass or body mass index (BMI) of either men or women, which is hardly compatible with the headlines suggesting that women find it harder to lose weight.
Where did the story come from?
The study was carried out by researchers from the University of Missouri and other institutions in the US and was funded by the National Institutes of Health.
The study was published in the peer-reviewed journal Metabolism.
The Mail’s headline and main body of the article are misleading as they suggest the study found that women have to do more exercise than men to lose weight.
This very small study only looked at people with type 2 diabetes, and all of its findings relate to differences in blood pressure recovery following a hand grip test in men and women.
Somewhat confusingly, the Mail reported that the study included just under 75 people, but the current publication only analysed results for 22 people.
It is possible that the Mail read a press release reporting 75 people rather than looking at any individual peer-reviewed evidence.
What kind of research was this?
This was a small, experimental study looking at differences in cardiovascular response (such as changes in blood pressure levels), and the nerve signals that control those responses, to exercise between men and women with type 2 diabetes.
The researchers say that some aspects of cardiovascular and neural responses to exercise differ between certain groups, such as:
- lean and obese people
- those with and without type 2 diabetes
- men and women
However, they say that no study has looked at gender differences in both of these responses to exercise in people with type 2 diabetes.
What did the research involve?
The research included 22 people with type 2 diabetes (10 men and 12 women), who were aged 40 to 60 years old. These people took part in a 16-week exercise programme which required them to walk for 30 minutes a day on four days of the week at 65% of their peak oxygen consumption (aerobic capacity). This was increased to 45 minutes from week eight onwards. They received one day per week of one-on-one exercise supervision, and worked on their own for the other three days.
Before and after the 16-week exercise programme they took various tests. In addition to the treadmill test to measure their peak oxygen consumption, they measured their height, weight and BMI. They also had their isometric handgrip (IHG) measured, which involved sitting with their elbow flexed to 90° and squeezing a handgrip machine – this measures grip strength – as hard as possible with the dominant hand (the right hand in right handed people, and the left hand in left handed people). This was performed three times, one to two minutes apart.
Heart rate variability was measured on an electrocardiogram (ECG), blood pressure was measured and blood samples were taken to look at glucose and insulin concentrations.
The researchers used statistical methods to look at before- and after-exercise programme changes in these variables, and also looked at differences between the men and women.
What were the basic results?
At the start of the study, men weighed more than women but had a lower percentage of body fat. There were no differences between men and women in age or fasting blood-sugar or insulin levels.
Exercise training did not make a difference to fat mass, weight, blood-sugar or insulin levels of either men or women.
Before the exercise programme, men had higher maximum oxygen capacity than women, and exercise training significantly improved the maximum oxygen capacity of both men and women.
Similarly, men had higher starting IHG strength than women, though the exercise programme had no effect on IHG strength in either group.
Men and women had similar heart rates before the exercise programme and the programme did not change this.
When they looked at their blood pressure change immediately after performing the IHG test, blood pressure increased in both sexes after the test, and the exercise programme did not change this.
The only two significant differences found between the two groups was that both before and after the exercise programme, women had less immediate reduction in blood pressure after the tests than men (suggesting that the women’s arteries took longer to ‘recover’ to their resting blood pressure).
Furthermore, in men, their blood pressure recovery after IHG improved after the exercise programme compared to what it had been before, but this did not happen in women.
How did the researchers interpret the results?
The researchers conclude that differences in blood pressure recovery immediately following IHG may be attributed to differences between men and women in their autonomic cardiovascular response (for example, how our bodies ‘automatically’ control our blood vessel response). The researchers observed an improvement in this autonomic response following aerobic exercise training in obese men, but not in obese women with type 2 diabetes. This, they say, suggests that men have a better autonomic response to aerobic exercise training.
This study does not find, as the headlines suggest, that women have to work harder to lose weight.
It was an extremely small experimental study with a sample of 10 men and 12 women with diabetes, and was assessing cardiovascular and neural responses to exercise. The study had nothing to do with weight loss.
The clinical significance of these findings in this very small number of people with diabetes is hard to determine. The study doesn’t say how this difference would relate to differences in the genders’ ability to lose weight.
The 16-week exercise programme had no effect on the fat mass of either men or women. In fact, the women showed a very small decrease in their BMI following the exercise programme (36.0 down to 35.4) while men’s went up by a fraction (39.1 to 39.2).
This effect was not statistically significant in either sex but the findings are hardly compatible with headlines suggesting that women find it harder to lose weight.
Men and women who are interested in losing weight can get further information from the NHS Weight loss plan.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.