The structure provided by school settings even with no specific obesity-intervention may prevent weight gain. This meta-analytic study considered this premise by examining weight outcomes from control groups in published randomized controlled trials of school-year obesity-related interventions conducted in-school and out-of-school.
A systematic review and random-effects meta-analysis were conducted in accordance with Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Databases were systematically searched and resulted in 1976 unique citations, with 14 retained for analysis. Analyses examined the change in weight outcomes among control group participants.
For studies (N = 6) reporting body mass index (BMI) (kg/m ) the overall standardized mean difference (SMD) from pre- to post-intervention was 0.085 (raw units 0.278 kg/m ); for studies (N = 9) reporting zBMI, the SMD was 0.022 (0.020 z-scores), for studies (N = 2) reporting waist circumference (cm), the SMD was 0.149 (1.609 cm); for studies (N = 2) reporting BMI percentile, the SMD was 0.064 (0.985 percentiles); and for studies (N = 1) reporting percent body fat, the SMD was 0.031 (0.30 percentage).
Children assigned to control conditions (as part of school-based obesity-related interventions) experience, on average, minimal changes in weight outcomes during the school year. Therefore, routine practices of schools may protect against unhealthy weight gains.

© 2020 American School Health Association.