Dietary impact on infants' gut microbiota and its capacity in SCFA metabolism: a longitudinal Dutch cohort study

Background: The infant gut microbiota (GM) matures rapidly during early life with complementary feeding marking a pivotal dietary shift that can shape long-term health trajectories. Detailed insight into how timing and composition of solid food introduction influences the composition and metabolic potential of the infant microbiome remains, however, limited. This study aimed to evaluate the impact of complementary feeding dynamics on the infant GM. Methods: We conducted longitudinal whole metagenomic sequencing of fecal samples collected at 4, 5, 6, 9, 11, and 14 months of age from 112 Dutch infants in the LucKi Gut cohort. Based on dietary questionnaires, infants were grouped into three distinct dietary classes of complementary feeding. Results: Infants introduced earlier to a wider variety of solid foods exhibited more diverse and mature gut microbiota already at 4 months, with increased abundance of butyrate-producing taxa such as Flavonifractor plautii . Their microbiomes also showed enhanced capacity to degrade dietary fibers like xylan and rhamnogalacturonan, suggesting accelerated development of metabolic functionality. Functional profiling revealed early enrichment in genes involved in butyrate synthesis, pointing to a link between early feeding diversity and SCFA-producing potential. Conclusions: Our findings highlight that early and diverse complementary feeding fosters a functionally mature microbiota with enhanced fiber degradation and butyrate production capacity. These microbial trajectories may influence immune and metabolic development, underscoring the importance of timely dietary diversification in infancy.