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Obesity · Journal article
Journal of the International Society of Sports Nutrition · September 8, 2026
Raises a question worth testing. It does not answer one.
This is an exploratory descriptive comparison of gut microbiome functional potential and fecal metabolites in two ultramarathoners with contrasting BMI and race outcomes. The authors acknowledge post hoc selection bias, confounding, and explicitly frame findings as hypothesis-generating rather than causal, and call for larger cohort studies.
Exploratory post hoc case-comparison study. Two ultramarathoners selected post hoc from participants in the same single-stage 217 km mountain ultramarathon; one with normal BMI and fast finish time, one with obesity and slow finish time.. Intervention: Participation in single-stage 217 km mountain ultramarathon; microbiome and metabolite analysis of pre- and post-race fecal samples. Compared with: Case-to-case comparison between normal-BMI fast-finisher and obese slow-finisher; no separate control or reference group. n = 2.
Normal-BMI fast-finisher showed smaller observed differences in enzyme-coding functions post-race, with predominance of nucleic acid and protein biosynthesis functions Obese slow-finisher showed larger observed differences in predicted functional potential between pre- and post-race samples Selective short-chain fatty acid changes observed in normal-BMI fast-finisher; reductions across all analyzed SCFAs in obese slow-finisher
Safety was not reported in the material analysed. Check the source before drawing any conclusion about harm.
This hypothesis-generating work does not support clinical decisions. Clinicians and researchers should view these descriptive observations as preliminary signals requiring validation in larger, prospectively designed cohorts with measured dietary intake and controlled confounding.
An exploratory case comparison of two ultramarathoners with post hoc selection, descriptive findings only, no statistical testing or comparator group, and the authors explicitly state these are hypothesis-generating observations rather than causal evidence.
As stated by the source record.
Quoted from the source exactly as published.
This hypothesis-generating work does not support clinical decisions. Clinicians and researchers should view these descriptive observations as preliminary signals requiring validation in larger, prospectively designed cohorts with measured dietary intake and controlled confounding.
Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.
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.
Taken from the source record, never inferred. Follow any of these and new work involving them reaches your briefing.