Exclusive breastfeeding is associated with the gut microbiome maturation in infants according to delivery mode.

Exclusive breastfeeding (EBF) plays a crucial role in infant gut microbiome assembly and development. However, few studies have investigated the effects of EBF in restoring a perturbed microbiome. In this study, we applied whole metagenomic sequencing to assess the gut microbiome assembly in 525 Brazilian infants from 3 to 9 months of age of the Germina Cohort, demonstrating the early determinants of microbial taxonomy and function modulation. Our analysis shows that EBF alters the relative abundance of genes related to the microbiome taxonomy and function, with effects varying by delivery mode. EBF alters the pattern of carbohydrates, lipid metabolism, and cell structure pathways depending on the delivery mode. The microbiome age is closer to chronological infant age in EBF than in non-EBF infants, meaning a lower microbiome maturation index (MMI). Using a complementary machine learning approach, we show that , , and , as well as vitamin K and o-antigen pathways contribute strongly to EBF prediction. Moreover, EBF influences the microbiome maturation in early life, toward a microbiome age more similar to the chronological infant's age.