The Gut Microbiota of Peruvian Children Under the Age of Two During the Complementary Feeding Period

The gut microbiota plays a crucial role in early childhood development. Dysbiosis in this community has been linked to risk of disease. The transition from an exclusive milk-based diet to complementary feeding and eventual weaning is crucial for the development and maturation of the gut microbiota. However, the impact of breastfeeding duration during the complementary feeding period (typically 6 to 24 months of age) on microbial development trajectories remains incompletely characterized. Here, we investigated whether prolonged breastfeeding during the complementary feeding window influences gut microbiota succession by comparing children who continued breastfeeding with those who were fully weaned at the same ages. We analyzed 16S rRNA gene sequencing profiles of fecal samples collected from a cohort of Peruvian children at 6, 12, 18, and 24 months of age. Samples were categorized into two groups: a complementary feeding group (BF), which received both complementary foods and breast milk, and a post-weaning group (NBF), which had stopped receiving breast milk for over 7 days. We conducted both alpha and beta diversity to assess within- and between-sample microbial variation. Relative abundances of microbial taxa at the phylum and genus levels were also quantified. The results showed a clear age-related increase in both species richness and species evenness across early childhood, while BF had more gradual changes relative to NBF. Marked differences in community composition were observed between BF and NBF children at 12, 18, and 24 months, respectively. Children who continued breastfeeding maintained a <i>Bifidobacterium</i>-rich, lower-diversity microbiota for a longer period, whereas weaned children at the same age exhibited accelerated microbiota development toward an adult-like profile enriched in Bacteroidota and Bacillota (formerly Firmicutes). These findings suggest that breastfeeding during the complementary feeding period exerts a significant influence on gut microbiota development through the first two years of life, which is most likely independent of complementary food. The study provides potential implications for children's health and nutrition guidelines from a perspective of gut microbiota succession.