Shared patterns of human milk composition link mammary gland function to infant growth.

The mammary gland produces nutrient-rich human milk (HM), yet how mammary functional state shapes HM composition and infant outcomes remains poorly understood. We used HM multi-omics - metabolomics, proteomics, micronutrients, macronutrients, and HM oligosaccharides - across 1,543 samples from three cohorts, including two randomized trials, as a noninvasive readout of mammary functional state. Trajectory modeling and multi-omic integration showed that maternal supplementation improved recovery from early growth faltering and revealed a shared HM compositional axis linking maternal nutrition to infant growth. Machine learning, with Human Protein Atlas-informed proteomics, identified seven HM biomarkers reflecting variation across key mammary domains, indexing milk synthesis, barrier integrity, and immune/repair activity. Elevated valerylcarnitine and low pantothenic acid emerged as metabolic signals linking mammary functional state to infant growth.