Nutritional and Physiological Demands Shape the Gut Microbiome of Female World Tour Cyclists

This cross-sectional study investigated whether elite female World Tour cyclists have a specific gut microbiome compared to non-athlete female controls, potentially resulting from the unique physiological and dietary demands of high-level endurance cycling. Fourteen female cyclists and thirteen matched controls provided fecal samples during a period of reduced training (off-season cycling). The samples were analyzed using 16S rRNA gene sequencing and short-chain fatty acid (SCFA) quantification. The results revealed significant differences in microbiome composition. The cyclists showed a higher abundance of Bacteroidota (72.7% vs. 15.3%) and a lower abundance of Firmicutes (22.1% vs. 62.5%) compared to the controls, along with reduced alpha-diversity (Shannon index, p < 0.05). Fiber-fermenting families such as Lachnospiraceae and Ruminococcaceae were depleted, consistent with a carbohydrate-focused and relatively low-fiber diet. Interestingly, fecal SCFA levels did not differ, suggesting functional adaptation of the microbiome. These findings indicate that the elite female cyclists may have developed a "performance-adapted" gut microbiome. However, due to the cross-sectional design, causality cannot be established, and the long-term health implications remain uncertain.