Abstract
INTRODUCTION: Obesity is a global health problem, with an impact on future health. Early factors such as infant feeding and rapid weight gain (RWG) may play a role in its development. However, their contribution is not fully understood. OBJECTIVE: To analyse associations and potential interactions between the type of infant feeding during the first 4 months of age, RWG and later development of obesity in children at 6 years of age. MATERIALS AND METHODS: This observational longitudinal study examines growth in 834 children born at term with adequate weight for their gestational age. Data were collected from birth to 6 years, focusing on weight, height and body mass index (BMI) z-scores. The relationships between infant feeding, RWG, and BMI at 6 years were explored using mediation models. RESULTS: Formula-fed infants showed higher BMI z-scores and obesity prevalence at 6 years compared to exclusively breastfed infants (p = 0.012 and p = 0.003 respectively). RWG also was associated with higher BMI z-scores and obesity (p < 0.001 in both cases), with formula-fed infants more likely to experience RWG (39.7% vs. 32.2%; p = 0.036). Mediation analysis revealed that the association between feeding type and BMI at 6 years is partly positively mediated by infant RWG up to 6 months. CONCLUSIONS: Infant feeding practices, particularly exclusive breastfeeding in the first 4 months, are associated with weight and BMI trajectories up to 6 years. Rapid weight gain mediates this relationship in the first 6 months, but from 6 to 12 months.