Effectiveness of a School-Based Obesity Prevention Programme on Body Composition and Physical Activity Among Adolescents in Lagos State

Childhood and adolescent obesity rates are rising in Nigerian urban centres, necessitating evidence-based school-based prevention programmes tailored to the local context. This study evaluates the effectiveness of a structured school-based obesity prevention programme on body composition and physical activity levels among secondary school adolescents in Lagos State, South West Nigeria. A cluster randomised controlled design was employed, with six schools randomised to intervention and six to a waitlist control condition. The 20-week programme combined structured daily physical activity sessions, nutrition education classes, and parental engagement workshops. Outcome measures included body mass index, waist circumference, percentage body fat estimated via bioelectrical impedance, and physical activity measured using accelerometry. Analysis used mixed-effects models accounting for clustering. Findings demonstrate statistically significant reductions in body mass index z-score and waist circumference in the intervention group compared to controls at 20 weeks. Percentage body fat reduction is significant among students in the overweight-obese category at baseline, with smaller but significant effects in the healthy-weight group. Accelerometry data confirm significant increases in moderate-to-vigorous physical activity minutes per day in the intervention group. Intervention effects are sustained at a 12-week follow-up assessment. The study identifies parental engagement and school leadership support as critical implementation fidelity predictors. Recommendations include national adoption of the programme model and investment in teacher training for delivery. Keywords: obesity prevention, school-based programme, body composition, physical activity, Lagos State