Breastfeeding type is associated with urinary metabolic changes in early life: influence of sex and early weight gain in healthy term infants

Perinatal factors are key modulators of neonatal metabolism and may contribute to long-term health trajectories. However, the metabolic adaptations underlying these early-life influences remain poorly characterized. In this study, we comprehensively characterized neonatal urinary metabolic profiles associated with multiple perinatal factors in full-term, healthy, breastfed infants at one month of age. Ninety-six urine samples from full-term, healthy, breastfed infants at one month of age were analyzed using liquid chromatography–mass spectrometry (LC–MS) and nuclear magnetic resonance (NMR). Exploratory multivariate analyses identified the maternal and infant factors most strongly associated with urinary metabolic variation, followed by multiblock integration to characterize the biological functions associated with the identified metabolic signatures. Breastfeeding type (exclusive, n = 79; mixed, n = 17) emerged as the factor most associated with urinary metabolic variability and was associated with differences in metabolites related to carbohydrate and lipid metabolism, gut microbiota, oxidative status, and vitamin handling, among others. Infant sex was also associated with metabolic differences, particularly affecting steroid metabolism, amino acid profiles, and mitochondrial-related compounds. In addition, weight gain during the first month of life was associated with variation in metabolites related to amino acid metabolism, gut-microbiota and antioxidant pathways. Urinary metabolomics revealed distinct metabolic signatures associated with early-life exposures. Among the factors studied, breastfeeding type (mixed vs. exclusive) was associated with the most pronounced differences in the urinary metabolome. These findings highlight the potential of urinary metabolomics for investigating early-life metabolic adaptations and provide a basis for future studies exploring the relationship between infant feeding and metabolic programming.