Obesity prevention programs for children and youth: why are their results so modest?

The purpose of this paper is to critically reflect upon the mixed/modest results of the primary studies related to the effectiveness of physical activity enhancement and improving nutritional intake in obesity prevention programs for children and youth. The results of a recent review of this topic that included 57 randomized controlled trials provide the basis for this discussion. Only four primary studies reported both statistically and clinically significant outcome differences between intervention and comparison groups. Although there are some similarities, there are differences among the four studies. These differences relate to program duration, frequency and intensity, targeted age of participants and level of involvement of students, the school as a community/institution and parents. Frequent methodological limitations of the studies included inadequate sample selection, lack of masking of outcome assessors, inappropriate data analysis and lack of important sub-analyses. Program design and implementation issues included lack of monitoring of program integrity and 'dose' received by participants. Theoretical basis for interventions were rarely stated and never used to explain the results. The effectiveness of parental involvement is unclear. The question of statistical versus clinical significance needs to be addressed by clinical experts. Based on this reflection, several potential future directions are outlined.