A systematic review and meta-analysis of the overall effects of school-based obesity prevention interventions and effect differences by intervention components

Background: Childhood obesity is a serious public health concern. School-based interventions hold great promise to combat the rising trend of childhood obesity. This systematic review aimed to assess the overall effects of school-based obesity prevention interventions, and to investigate characteristics of intervention components that are potentially effective for preventing childhood obesity. Methods: We systematically searched MEDLINE, CENTRAL and Embase databases to identify randomized- or cluster randomized- controlled trials of school-based obesity interventions published between 1990 and 2019. We conducted meta-analyses and subgroup analyses to determine the overall effects of obesity prevention programs and effect differences by various characteristics of intervention components on body mass index (BMI) or BMI Z-score of children. Results: This systematic review included a total of 50 trials (reported by 56 publications). Significant differences were found between groups on BMI (- 0.14 kg/m(2) (95% confidence interval: - 0.21, - 0.06)) and BMI Z-score (- 0.05 (- 0.10, - 0.01)) for single-component interventions; significant differences were also found between groups on BMI (- 0.32 (- 0.54, - 0.09) kg/m(2)) and BMI Z-score (- 0.07 (- 0.14, - 0.001)) for multi-component interventions. Subgroup analyses consistently demonstrated that effects of single-component (physical activity) interventions including curricular sessions (- 0.30 (- 0.51, - 0.10) kg/m(2) in BMI) were stronger than those without curricular sessions (- 0.04 (- 0.17, 0.09) kg/m(2) in BMI); effects of single-component (physical activity) interventions were also strengthened if physical activity sessions emphasized participants' enjoyment (- 0.19 (- 0.33, - 0.05) kg/m(2) in BMI for those emphasizing participants' enjoyment; - 0.004 (- 0.10, 0.09) kg/m(2) in BMI for those not emphasizing participants' enjoyment). The current body of evidence did not find specific characteristics of intervention components that were consistently associated with improved efficacy for multi-component interventions (P > 0.05). Conclusions: School-based interventions are generally effective in reducing excessive weight gain of children. Our findings contribute to increased understandings of potentially effective intervention characteristics for single-component (physical activity) interventions. The impact of combined components on effectiveness of multi-component interventions should be the topic of further research. More high-quality studies are also needed to confirm findings of this review.