Associations of Self-Reported Physical Activity with Gut Microbial Diversity and Community Structure in Young, Apparently Healthy Korean Men

Evidence linking physical activity (PA) to the gut microbiota in Korean populations remains limited. We examined associations of self-reported PA with gut microbial diversity and community structure in 49 young, apparently healthy Korean men. Participants were classified into study-specific categories based on total metabolic equivalent minutes per week (MET-min/week): C1 (≤1500), C2 (1501–3000), and C3 (≥3001). Fecal microbiota were profiled using 16S rRNA gene V4 sequencing, and diversity analyses used 100 repeated rarefactions to 22,000 reads per sample. In primary continuous analyses, total MET-min/week was positively correlated with the Shannon index (ρ = 0.3567, q = 0.0356) after false discovery rate (FDR) correction, whereas associations with Observed features and Fisher’s alpha did not remain significant. Total MET-min/week was also associated with variation in microbial community composition across all four beta-diversity metrics, explaining 2.7–3.3% of the variation. In secondary categorical analyses, alpha diversity did not differ significantly among PA categories after FDR correction, whereas Jaccard and unweighted UniFrac showed FDR-significant differences. No robust genus-level association was identified after FDR correction and compositional sensitivity analysis. These exploratory findings indicate small cross-sectional associations and should be interpreted cautiously because the primary analyses were largely unadjusted for potential lifestyle confounders.