Modeling children’s weight growth trajectories: sex, country, and rural–urban differences in four low- and middle-income countries

Modeling children’s weight growth trajectories provides important insights into how biological and contextual factors shape development, yet most longitudinal research in low- and middle-income countries (LMICs) has focused on height rather than weight. We analyzed data from the Younger Cohort of the Young Lives study in Ethiopia, India, Peru, and Vietnam (2002–2016). Children with fewer than five weight measurements or missing key variables were excluded. The final analytic sample included 7,140 children contributing 35,700 observations. Weight trajectories from ages 1 to 15 years were modeled using a three-parameter logistic nonlinear mixed-effects model with fixed effects for sex, country, and rural–urban residence, and random effects on all three parameters to capture between-child heterogeneity. The model revealed marked variability in asymptotic weight, timing, and growth rate. Peak growth velocity occurred at 13.9 years (~ 3.3 kg/year), with males peaking earlier than females and urban children peaking earlier than rural peers. Across countries, children in Peru and Vietnam had higher growth velocities and asymptotic weights than those in Ethiopia and India. Urban children consistently showed higher trajectories than rural children. Variance components and intraclass correlations confirmed substantial between-child heterogeneity in growth patterns. Children’s weight trajectories vary significantly by sex, country, and rural–urban residence. The findings highlight persistent disadvantages in rural Ethiopia and India alongside emerging risks of overweight in more urbanized Peru and Vietnam. Policies tailored to local contexts are needed to promote healthy weight growth across childhood and adolescence.