Interpret results with caution

The conclusions drawn by the authors of the March 31 meta-analysis of the effect of school-based physical activity interventions on body mass index (BMI) in children are troubling.

Their analysis found that school-based physical activity interventions implemented in the general school population do not improve BMI. This says nothing about effects of physical activity on the subgroup of children who are overweight or obese; it says nothing about the role of physical activity in preventing weight gain in children of healthy weight; and it cannot account for changes in body composition among children (a limitation they note).

Physical activity should be an integral part of population-based health promotion efforts. We should be working to enhance these efforts in schools. We should avoid drawing conclusions (with policy implications) about the impact of physical activity on childhood obesity using data and methodological approaches that have inherent limitations.