Dynamic Succession of the Early-Life Gut Microbiota and the Regulatory Role of Human Milk Oligosaccharides

Early-life nutrition and the gut microbiota interact to shape host health programming. During early-life development, spanning the neonatal period of initial gut colonization through infancy to toddlerhood, the gut microbiota undergoes dynamic succession driven by feeding patterns, host genetic background, environmental exposures, and other intrinsic and extrinsic factors, among which early feeding practices play a particularly prominent role. Among these factors, human milk oligosaccharides (HMOs), key bioactive components of human milk, contribute to the shaping of infant gut microbial ecology by selectively supporting HMO-utilizing bacteria, influencing microbial metabolism and cross-feeding, and exhibiting structure- and context-dependent effects on pathogen–host interactions, intestinal barrier function, and immune responses. This narrative review summarizes the succession patterns of the gut microbiota in early life and the core regulatory mechanisms by which HMOs shape infant gut microbial ecology, aiming to provide a conceptual basis for understanding the potential long-term health implications of early nutritional interventions.