Exploratory case comparison of gut microbiome functional potential in ultramarathoners differing in adiposity and finish time

Understanding variations in gut microbial functional potential among endurance athletes may inform future personalized nutritional strategies. This exploratory case-comparison study aimed to investigate predicted microbial functional potential using shotgun metagenomic sequencing and fecal metabolites, in two post hoc-selected runners who represented extreme and contrasting outcomes from the same single-stage 217 km mountain ultramarathon: a normal-BMI fast-finisher and an obese slow-finisher. The main descriptive findings suggest that the normal-BMI fast finisher exhibited smaller observed differences among the analyzed enzyme-coding functions and pathways in the sample collected after race completion, with a predominance of enzyme-coding functions associated with nucleic acid-related processes and protein biosynthesis. In contrast, the obese slow-finisher showed larger observed differences in predicted functional potential between the pre- and post-race samples. Distinct fecal metabolite patterns were also observed, with selective short-chain fatty acid (SCFA) changes in the normal-BMI fast-finisher and reductions across all analyzed SCFAs in the obese slow finisher. Given the limitations of this study, including the confounding effects of adiposity, unmeasured dietary intake, and post hoc selection bias, these descriptive observations provide hypothesis-generating data rather than establishing causal relationships with performance. Taken together, these findings encourage further investigation in larger cohorts.