Infant Feeding and Growth Patterns in Japanese Children: A Nationwide Secondary Analysis

<b>Objectives</b>: To examine age-specific growth patterns derived from Japanese cross-sectional data according to infants' feeding and determine whether differences persist through preschool age. <b>Methods</b>: We analyzed secondary data from the 2023 National Growth Survey on Preschool Children in Japan, a single-wave nationwide cross-sectional survey. The participants were 8028 singleton, term-born, appropriate-for-gestational-age children aged 0-60 months without major health conditions. The feeding history up to 24 months was reported by parents and categorized as breastfed, formula-fed, or mixed-fed. Anthropometric measurements were obtained at a 1-month postnatal checkup or at checkups arranged for the survey, converted to standard deviation scores using Japanese references, and modeled with growth curves using the Lambda-Mu-Sigma method to summarize cross-sectional distributions by age. The feeding groups were compared at selected ages. <b>Results</b>: Breastfed infants were smaller in length/height and weight than formula-fed peers during the first 2 years, with the largest differences in infancy. The mean stature in the feeding groups became similar at older ages; by 60 months, standard deviation scores for stature and weight were comparable across the feeding groups. Head circumference patterns up to 36 months were not different by the feeding category. <b>Conclusions</b>: In Japan, early size differences by the feeding group show age-related convergence of cross-sectional group means by preschool, and head circumference patterns are similar across the groups. These findings support breastfeeding as sufficient for long-term growth without unnecessary formula supplementation.