Human Milk Microbiota and Oligosaccharides: Origin, Structure, Impact Factors, and Benefits for Infant Health

Early life is an essential period for the establishment of the gut microbiota and is considered a critical window for intervention. Breast milk serves as a natural food for babies and contains a variety of bioactive ingredients that promote healthy growth. The active ingredients in breast milk that are closely related to infant gut development, such as human milk microbiota (HMM), are the primary source of infant gut microbiota. Human milk oligosaccharides (HMOs) can reach the infant colon intact and serve as fermentable substrates for specific gut microbiota, thereby helping shape the infant gut microbiota. The absence of these active ingredients in milk formula is strongly associated with health problems and abnormal gut microbiota in infants. This review provides an overview of the changes in the gut microbiota of the host at various stages of development, summarizing recent research on the active ingredients of early-life ingested food-breast milk, including HMM and HMOs, their origin, structure, impact factors, and contribution to infant health benefits. It also reviews major strategies for utilizing HMOs for infant gut probiotics and next-generation potential probiotics, providing a reference for the later development of formula milk and related nutritional products.