Exercise intensity as a modulator of gut microbiota and host metabolic health in obesity

The gut microbiome is shaped by complex interactions among host, environmental, and lifestyle factors, with exercise emerging as a reported modulator. Growing evidence suggests that exercise intensity, ranging from low to high, can differentially influence gut microbial composition, diversity, and functional outputs relevant to metabolic health. This narrative review synthesizes current findings examining intensity-dependent microbial adaptations in the context of obesity. Across animal models (n = 17) and limited human studies (n = 5), moderate-intensity training (MIT) and high-intensity interval training (HIIT) produce the most consistent microbiota shifts, while low-intensity training (LIT) exerts minimal effects. Reported taxa associated with beneficial outcomes consistent across animal and human investigations include Akkermansia (G), and Christensenellaceae (F). Mechanistically, intensity-dependent alterations in microbial communities may influence obesity-related pathways through modulation of short-chain fatty acid (SCFA) and bile acid metabolism, gut barrier integrity, endotoxemia, and inflammatory signaling. HIIT and MIT are linked to improved expression of tight junction proteins (ZO-1, Claudin, Occludin), reducing circulating lipopolysaccharide (LPS), and increasing SCFA-producing taxa; thus, supporting a role for the gut microbiome in mediating exercise-induced metabolic benefits. However, inconsistent findings between species, interindividual variability, and considerable heterogeneity in exercise intervention duration across both animal (4-16 weeks) and human (3-12 weeks) studies, as well as limited longitudinal human studies, underscore the need for deeper mechanistic investigations. Future research should employ metagenomic and metatranscriptomic profiling, integrate sex- and diet-stratified longitudinal designs, and clarify causal links between exercise-responsive taxa, microbial metabolites, and host physiology. Collectively, these data highlight exercise intensity as a key determinant of gut microbiome dynamics and reinforce the need for integrative, translational approaches to define its therapeutic potential for obesity and metabolic disorders.