Nutritional and environmental determinants of maturation and disruption of the early life gut microbiome: A narrative review

Abstract

The first 1000 days of life represent a critical window for gut microbiome assembly, with lifelong implications for child growth, immune development, and disease risk. This review synthesizes evidence on maternal, perinatal, and especially nutritional factors that influence early‐life intestinal colonization and highlights the consequences of microbial disruptions during this period. In utero exposures and birth‐associated factors can profoundly shape microbial development, reducing diversity and beneficial taxa. Nutrition exerts a particularly dominant and modifiable influence: breastfeeding supports Bifidobacterium‐rich communities, while formula use and early complementary feeding shape microbiota diversity and metabolic function. Dietary quality, fiber intake, and food diversity are key determinants of microbial maturation and resilience. Undernutrition and inadequate diets contribute to microbial dysbiosis, creating a self‐reinforcing cycle of malabsorption, growth failure, and long‐term metabolic consequences. Early microbial perturbations are associated with a range of acute and chronic diseases, including necrotizing enterocolitis, obesity, type 1 diabetes, inflammatory bowel disease, and atopic disorders. Strategies to restore microbial balance require further validation, particularly in nutritionally vulnerable populations. The absence of a universal definition for a “healthy” pediatric microbiome limits the development of targeted interventions. Emerging metrics, such as microbiota‐for‐age z ‐scores and functional microbiome profiling, may help define microbiota maturity and therapeutic efficacy.