Effects of a 217-km mountain ultramarathon on the gut microbiota of an obese runner: A case report.

Obesity is characterized by specific changes in the composition of the gut microbiota (GM). Exercise can contribute to the modulation of GM. This is the first case study to analyze the composition and metabolism of the GM of an obese runner in a single-stage mountain ultramarathon (MUM) with a mileage of 217 km. Fecal samples were collected 7 days before the race (T0), 15 min after the end of the race (T1), and 7 days after the end of the race (T2). GM composition was analyzed by real-time PCR and shotgun sequencing. We observed a decrease in Bacillota/Bacteroidota ratio and α-diversity after the race. After the 217-km MUM, we observed a decrease in symbiont microorganisms and a notable increase in harmful bacteria. In conclusion, we found that the 217-km MUM may have contributed to the intestinal dysbiosis of the obese runner.