The effects of sustained fitness improvement on the gut microbiome: A longitudinal, repeated measures case-study approach

Abstract Objective The composition and metabolic function of the gut microbiome in the elite athlete differs from that of non-athletes. However, short-term fitness improvement in the sedentary adult does not replicate the microbiome characteristics seen in the athlete. Whether sustained fitness improvement over a prolonged period can lead to pronounced and beneficial alteration in the gut microbiome is unknown. The objective was to explore this possibility. Methods This study used a repeated-measures, case-study approach to explore changes in the gut microbiome of two unfit volunteers undertaking progressive exercise training over a 6-month period. Training was to culminate in the completion of a marathon or Olympic-distance triathlon. The volunteers were sampled every two weeks for six months and microbiome, metabolome, diet, body composition, and cardiorespiratory fitness data were recorded. Results Both participants completed their respective goals with improved body composition and fitness parameters over the training period. Increases in α-diversity of the gut microbiota occurred with sustained training and fluctuations occurred in response to training events (e.g., injury, illness and training peaks). Participants’ fat mass and BMI reduced during the study and was significantly associated with increased urinary measurements of N-methyl nicotinate (P value < 0.001) and hippurate (P value < 0.05), and decreased phenylacetylglutamine (P value < 0.05). Conclusion These results suggest that sustained fitness improvements result in alterations to gut microbiota and physiologically-relevant metabolites. This study provides longitudinal analysis of the response of the gut microbiome to real-world events during progressive fitness training, including intercurrent illness and injury.