Gut Microbiome and Training Adaptation: A Narrative Review of Evidence from 2018–2026

Abstract

Background: The gut microbiome has emerged as a potential modifier of exercise physiology through effects on nutrient metabolism, intestinal barrier integrity, immune regulation, microbial metabolite production, and gut–brain communication. However, microbial changes reported after training are heterogeneous, and their contribution to persistent human training adaptation remains uncertain.  Aim: This narrative review examines evidence from 2018 to 23 July 2026 on how endurance, resistance, and combined exercise affect the gut microbiome and whether microbiome-related pathways influence performance, recovery, adherence, and long-term adaptation.  Material and Methods: A targeted search of PubMed/MEDLINE, official publisher platforms, and reference lists was performed for peer-reviewed human interventions, athlete studies, systematic reviews, meta-analyses, and mechanistic animal experiments. Evidence was synthesized qualitatively because of substantial heterogeneity in populations, exercise prescriptions, dietary control, sequencing methods, metabolite assays, and performance outcomes.  Results: Human endurance and combined training produce modest, variable, and often reversible microbiome changes influenced by factors such as diet, age, adiposity, exercise dose, medications, and baseline microbial composition. Resistance training improves neuromuscular function but usually causes limited group-level microbiome changes. Athlete microbiomes differ from those of sedentary individuals, although dietary and lifestyle confounding remains substantial. Animal studies suggest mechanisms involving microbial propionate, dopaminergic signaling, and bile-acid pathways, but direct human evidence that microbiome modification improves training adaptation remains insufficient.  Conclusion: Current evidence supports a bidirectional exercise–microbiome relationship but does not establish a universal athletic microbiome or justify routine microbiome-based training prescriptions.