Breast Milk, Mother, and Infant Triad as a Biological Complex

Human milk is the optimal food for the growing infant and breastfeeding has been associated with short- and long-term benefits for both infant and mother. Human milk composition is adapted to stages of infant development from the immunologically rich colostrum to energy dense mature milk. Recent studies have shown that the time of lactation, circadian rhythm, maternal diet, genetics, and even presence of maternal or infant infection can influence milk composition. Human milk, however, is not just a sum of single nutrients but a complex biofluid rich and organized in potentially functional and not just nutritive structures like exosomes, bacteria, and eukaryotic cells. The complexity of human milk, its importance for infant health, and development call for future research investments to characterize deeper milk composition beyond single nutrients to understand their function. Building global and regional references for human milk will also enable a better insight in nutrition requirements, inform guidelines, and provide recommendations adapted to lactating mothers.