Abstract
INTRODUCTION: This systematic review and meta-analysis investigate the long-term effects of primary school-based obesity prevention interventions on body-mass index (and z-scores), waist circumference (and z-scores) and weight status. METHODS: Four databases were searched for studies from date of inception until June 8th, 2021. We included randomized controlled trials (RCT) and non-RCTs investigating effects ≥12 months post-intervention of primary school-based interventions with intervention duration ≥6 months and containing a diet and/or physical activity component on outcomes of interest. Articles were assessed on risk of bias and methodological quality by RoB2 and ROBINS-I. Meta-analysis was performed and results were narratively summarized. Evidence quality was assessed with GRADE. RESULTS: Nineteen studies were included, 9 were pooled in a meta-analysis. No long-term effects were found on body-mass index (+0.06 kg/m(2) ; CI95% = -0.38, 0.50; I(2) = 66%), body-mass index z-scores (-0.08; CI95% = -0.20, 0.04; I(2) = 36%), and waist circumference (+0.57 cm; CI95% = -0.62, 1.75; I(2) = 13%). Non-pooled studies reported mixed findings regarding long-term effects on body-mass index, body-mass index z-scores and weight status, and no effects on waist circumference and waist circumference z-scores. Evidence certainty was moderate to very low. DISCUSSION: No clear evidence regarding long-term effects of primary school-based interventions on obesity-related outcomes was found. Recommendations for further research and policy are discussed. Prospero registration ID: CRD42021240446.