Can the bacteria that colonize an infant’s gut influence brain development years later? Over the past decade, research on the microbiota-gut-brain axis has grown at an extraordinary pace. What began as a handful of intriguing animal studies has evolved into large prospective human cohorts, systematic reviews, and mechanistic studies examining how the developing microbiome interacts with the immune system, metabolism, and nervous system during early childhood. In this podcast episode, I review three major sources of evidence that help put this rapidly evolving field into perspective: a 2025 narrative review synthesizing 237 studies, the landmark Swedish ABIS birth cohort that followed more than 16,000 children for over 20 years, and other prospective studies investigating how early-life microbial patterns may relate to later neurodevelopment. The episode explores what researchers currently know about the gut-brain axis, why the first years of life appear to represent a critical window for microbiome development, and
