Unraveling Stage-Specific Metabolites in Human Milk and Their Links to Maternal Physiology: Insights from a Mexican Population

<b>Background/Objective:</b> Human milk is an irreplaceable source of nutrition and is essential for the infant's growth and development right after birth and for early life stage survival. This study aims to characterize and compare the metabolite profiles of colostrum and transitional and mature milk using an untargeted GC-MS approach. Additionally, it explores potential correlations between the identified metabolites and maternal nutritional factors. <b>Methods:</b> This was a longitudinal, prospective, and observational study. We included human milk samples from 113 Mexican women who practiced exclusive breastfeeding. Partial least squares-discriminant analysis (PLS-DA) was performed to assess differences among lactation stages. Metabolites showing significant variation across lactation stages were further analyzed using Friedman tests with post hoc Wilcoxon tests and Bonferroni correction. Correlations with maternal anthropometric measures were evaluated. <b>Results:</b> Twenty-three metabolites were identified, including amino acids and derivatives, sugars, fatty acids, and energetic metabolites. Alanine and creatinine levels decreased during lactation, while aspartate, serine, and valine levels increased. Rhamnose level was higher in colostrum, whereas decanoic, dodecanoic, and tetradecanoic acid levels increased over time, and that of 11,14-eicosadienoic acid decreased. Lactic acid levels declined across stages. Negative correlations were found between several amino acids and maternal anthropometric variables, while glyceric acid, rhamnose and lactic acid correlated positively. <b>Conclusions:</b> Human milk metabolomic profiles display distinct, stage-specific variations shaped by maternal characteristics, reflecting the dynamic physiological and nutritional demands of the developing infant.