05/10/2010 - Articles

Preventing weight gain through exercise

By: Susan Aldridge, medical journalist, PhD


The equation for weight gain is a simple one – if calories in (through food) are greater than calories out (through exercise) then you will gradually gain weight. Therefore, exercise clearly plays an important role in balancing the equation, preventing weight gain and maintaining a healthy weight. But, the big unanswered question is – can you stay trim by exercise alone, if you do enough? A new study from researchers at Harvard Medical School, and elsewhere, set out to provide some answers.

They followed a group of over 34,000 healthy women of average age 54 for about 13 years, recording their weight and level of physical activity at regular intervals. Currently, US federal guidelines are to take 150 minutes a week of moderate intensity aerobic physical activity, which the researchers translated into 7.5 ‘metabolic equivalent hours (METs) per week. Note that some other recommendations are different – for instance, the Institute of Medicine recommends 60 minutes of moderate intensity exercise per day.

In this study, women were divided up according to whether they took less than 7,5 METs exercise a week, between 7.5 and 21 METs, and over 21 METs. The main outcome of the study was amount of weight gained. Overall, the women gained 2.6 kilograms (about six pounds) during the study, which is a very common experience as we age. Overall, there was no significant difference in weight gain between the women taking a lot of exercise (over 21 METs a week) and those taking not very much (fewer than 7.5 METs a week).

But when body mass index (BMI) was taken into account, a pattern did emerge. For women with a BMI of less than 25, the more exercise they took, the less weight they gained. For women whose BMI was 25 or more, level of exercise did not have any influence on how much weight was gained. The researchers studied the women of initially healthy weight (BMI less than 25) who managed to avoid weight gain throughout the study and found that they took an average of 21.5 METs of exercise per week (about 60 minutes a day). All the women were on their usual diet throughout the study. The findings suggest that exercise alone is only successful in preventing weight gain if you are already of a healthy weight. For the overweight or obese, calorie restriction is also necessary for preventing weight gain or shedding weight.



Lee I-M et al Physical activity and weight gain prevention Journal of the American Medical Association March 24/31 2010;303:1173-1179


Created on: 05/10/2010
Reviewed on: 05/10/2010

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