Modifiable risk factors in relation to changes in BMI and fatness: what have we learned from prospective studies of school-aged children?

Considerable interest and resources are currently being directed to primary and secondary prevention of childhood obesity among school-aged children. Intervention studies in this age group have yielded mixed results, begging the question as to whether the correct targets for intervention have been identified. To evaluate the evidence base, we reviewed prospective observational studies published in English between 1990-2007 that reported weight or fatness changes in relation to diet, physical activity, and sedentary behavior. Sugar-sweetened beverage consumption emerged as the most consistent dietary factor in association with subsequent increases in weight status or fatness. Other foods and eating patterns showed less consistent associations and when associations were present, magnitudes were generally small. This may reflect the known limitations of standard dietary methodology to assess meal patterns and dietary intake. Findings for physical activity showed more consistent inverse associations with fatness outcomes than for weight status, and as was found for dietary factors, magnitudes of association were modest. Sedentary behavior effects on weight status differ by gender in many studies, with many, but not all, showing greater positive associations among girls. The lack of consistency observed in the studies of sedentary behaviors may reflect the range of variable definitions, measurement challenges, and the changing nature of electronic media. The intrinsic interplay among eating patterns, activity and sedentary behavior adds further complexity to the interpretation of the results of these studies. More sophisticated approaches to the analysis of these complex data in future studies may maximize what is learned. Although the classic obesity risk factors seem to play a role in the development of excess weight and fatness, some more recently identified potential factors, such as sleep, warrant further investigation in prospective studies before they are ready for evaluation using more controlled study designs.