Resistance Training Reshapes the Gut Microbiome in a Longitudinal 8-Week Intervention in Sedentary Adults

Abstract Background The gut microbiome plays a critical role in metabolism, immunity, and aging. While endurance training has been shown to beneficially modulate the microbiome, the effects of resistance training remain less clear, with some studies reporting minimal changes. This project aims to investigate whether structured resistance training elicits significant changes in gut microbiome composition and diversity in sedentary, healthy adults. 150 participants (85 female, 63 male), between 24 and 61 years of age, completed an 8-week supervised resistance training program between May 2022 and July 2023 in the cities of Tübingen and Rottenburg, Germany. Session-level training data, including weights and repetitions, were recorded alongside metrics like load and compliance. Fecal samples were collected throughout the study period at designated timepoints for 16S rRNA gene amplicon sequencing to assess microbiome composition and for metabolomics analyses to evaluate microbial metabolic activity. Results No differences in microbial diversity were observed, and there were no significant changes in microbial community composition or fecal metabolomics across all participants post-training. However, within-individual microbial community changes significantly correlated with strength improvement (Pearson correlation coefficient r = 0.167, p = 0.0004), and significantly stronger shifts in beta diversity were observed in participants with ≥ 33% average strength gains compared to those with ≤ 12.2% gains (Kruskal-Wallis rank sum test, p = 0.08). In these high responders, differential abundance analysis revealed time-dependent microbial changes, with 27 taxa enriched or depleted by week 8 of training (ANCOM-BC2, ≥ 2-fold change, p ≤ 0.05). Notably, Faecalibacterium and Roseburia hominis—both associated with a healthier, anti-inflammatory microbiome—were significantly enriched. Many differentially abundant taxa belonged to the Lachnospiraceae family. Conclusions Resistance training drives significant, time-dependent gut microbiome changes, particularly in those demonstrating greater improvements in strength. These shifts mirror endurance training effects and may reflect improved overall health.