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This meta-analysis shows that exercise has very little effect on weight

Posted by JSShapiro on 02 Nov 2011 at 20:12 GMT

In this meta-analysis, the overall effect of exercise on weight was actually very small. Active adults had a BMI only 0.79 units lower than inactive adults (a weight difference of about 2 kilos), while exercise had no significant effect on children's BMI at all.

Here is another way of seeing just how tiny the effect of exercise was on obesity. For people with one copy of the obesity-producing FTO allele, inactivity raised their relative risk of obesity from 1.22 to 1.30, or an increase of about 7%. In comparison, long-term heavy smoking raises the odds ratio of lung cancer from 1.00 to around 10.00, a risk of about 1000%.

Yet, an accompanying editorial claims "genes may predispose to weight gain, but this weight can be lost by extra physical activity," as if exercise were enough to return obese people to a normal weight. And, the media is already interpreting this meta-analysis as saying that genes don’t matter, with Time Magazine headlining their article, “How Exercise Trumps Obesity Genes.”

The opening paragraph of this article talks about “apportioning responsibility for obesity.” Well, readers of the Time Magazine article certainly seem to be apportioning responsibility, with comments saying the obesity gene is next to “the stupidity gene,” that obese people have filthy, disgusting eating habits, and that obesity is a choice. If this was not the effect the authors of this article intended to convey, I suggest they contact Time Magazine, and any other media outlets featuring this research, and point out just how small the effect of exercise on obesity actually was in this population.

No competing interests declared.