The Gut Microbiome in Athletes: Mechanisms, Training Adaptations, and Implications for Performance — A Comprehensive Review

BackgroundThe gut microbiota is increasingly seen as a key regulator of functions relevant to athletic performance. Exercise alters microbial composition, while microbial metabolites influence metabolism, immunity, gut barrier integrity, and recovery. Despite rapid growth of research, findings are inconsistent, underscoring the need for clearer mechanisms. This review summarizes current evidence on the bidirectional relationship between training and the gut microbiota and its implications for performance. AimTo consolidate open-access research on links between gut microbiota, exercise physiology, and performance, focusing on metabolic pathways, gut–muscle communication, immune modulation, intestinal permeability, and training-specific effects. Material and MethodsThis narrative review draws on open-access literature up to 2025, identified through PubMed, PMC, and Google Scholar. Included studies comprise mechanistic animal work, observational data, randomized trials, and systematic reviews examining physical activity, microbiota composition, microbial metabolites, and performance in athletes. ResultsEndurance training induces microbial adaptations, including increases in taxa metabolizing lactate and generating propionate. Strength and HIIT training show more variable changes shaped by diet, training load, and metabolic health. Microbial metabolites—especially SCFAs—may enhance energy regulation, immune balance, and gut barrier function, though evidence remains fragmented and causality unclear. ConclusionThe gut microbiota is a dynamic component of exercise adaptation. While diverse and SCFA-producing microbes appear beneficial for metabolism, inflammation control, and recovery, overall findings are heterogeneous. More interdisciplinary research is needed to clarify causal pathways and support personalized, microbiome-based strategies in sports nutrition and training.