OBJECTIVE: Launching priority actions demand a comprehensive appraisal of the size effect that risk factors have on the burden of overweight and obesity. This study aimed to estimate the incidence of overweight and obesity among children and adolescents, with special emphasis on the role of specific risk factors.MATERIALS AND METHODS: Secondary analysis of data from the younger cohort of the Young Lives Study in Peru (2002-2017). The outcomes were: overweight and obesity, defined by the World Health Organization standards; whereas the exposures included caesarean birth, physical activity levels, sodas and sugar-sweetened beverages consumption, snacks consumption, and maternal body mass index (BMI). We used multilevel Poisson regression models, considering the repetitive nature of data, to estimate incidence rate ratios (IRRs) and population attributable fractions (PAFs).RESULTS: A total of 2052 children, mean age 1 (SD 0.4) year, and 50% girls, were enrolled at baseline. After 14 (SD 0.5) years of follow-up, the incidence of overweight and obesity were 7.9 (95% CI 7.6-8.2) and 2.2 (95% CI 2.0-2.4) per 100 person-year, respectively. Maternal BMI (IRRs 3.51; PAF 31.8%), low physical activity (IRR 1.64; PAF 27.4%), caesarean birth (IRR 1.63; PAF 11.4%), almost daily snack consumption (IRR 1.60; PAF 32.1%), and almost daily consumption of sweetened beverages (IRR 1.47; PAF 26.0%) increased the risk of developing obesity.CONCLUSIONS: This study provides evidence on the risk of overweight and obesity attributable to diet habits, physical activity and the obesogenic niche among children and adolescents in Peru, which may guide the implementation of evidence-based interventions.