.png)
If overweight women exercise to lose weight, they might reconsider their weight-loss plan. (Photos.com)
I am a fan of exercise. It is linked to various benefits for the body and brain. One thing that exercise is said to be beneficial for is weight loss.
However, exercise may not help people to shed pounds in meaningful amounts. But could it prevent individuals gaining weight over time?
U.S. scientists recently asked this question by looking at the relationship between physical activity and weight trends in a large group of more than 34,000 women over about a decade and a half. The results are published in the March 24 issue of the Journal of the American Medical Association.
This study is vast, but it needs to be remembered that it is epidemiological. That means it is useful for looking at the relationship between physical activity and weight. However, it cannot prove that such a link is causal.
If increased physical activity were to be found to be associated with reduced risk of weight gain, that would not prove that increased activity causes reduced risk of weight gain. Maybe those who are more active eat better, and perhaps this is the real reason why those who exercise more gain less weight.
With this caveat in mind, let’s have a look at what this study found.
On average, women gained 5.7 pounds over the course of the study. Physical activity was associated with less weight gain but only in women whose body mass index (BMI) was less than 25.
In other words, increased exercise was associated with reduced weight gain only in women who didn’t have a weight problem to begin with. Increased exercise appeared not to do much good for the women who needed it the most.
Let’s have a look at the apparent level of benefit in the women with BMIs of less than 25.
Levels of activity were defined by a measurement known as the metabolic equivalent of task or MET. Sitting quietly is 1 MET. The MET of an activity is the multiple of energy it uses compared to sitting quietly.
For example, if walking at a particular speed uses twice as many calories as sitting still, then this activity has a value of 2 METs. If the walking continues for an hour, the total energy burned can be expressed as 2 MET hours.
In this study, women were divided into three categories according to levels of activity. These bands were women engaged in activity equivalent to:
1. Less than 7.5 MET hours per week.
2. 7.5 to less than 21 MET hours per week.
3. 21 or more MET hours per week.
Those who exercised the most (group 3) were used as the reference group. Over a three-year period, additional weight gain in those in group 2 and group 1 was 0.3 pounds and 0.46 pounds, respectively. Although statistically significant, these benefits are modest at best.
Another finding of this study was that women of normal weight who were successful at gaining less than 5 pounds over the 13 years engaged in moderate-intensity activity for an average of about an hour a day.
My aim here is not to put anyone off taking exercise. However, it seems we have more evidence that in terms of weight loss, the payoff for exercise is quite underwhelming.
Dr. John Briffa is a London-based physician and author with an interest in nutrition and natural medicine. His Web site is Drbriffa.com
