Characterization of the Gut Microbiota Signature According to Physical Fitness and Its Implications for Intestinal Health.

The gut microbiota comprises all microorganisms inhabiting the digestive tract, evolving throughout life under the influence of various intrinsic and extrinsic factors. Under healthy conditions, the microbiota remains stable, resilient, and maintains a symbiotic relationship with its host. Conversely, dysbiosis refers to an alteration in microbial composition and function, which has been linked to diseases such as inflammatory bowel disease (IBD). IBD, including Crohn's disease and ulcerative colitis, is associated with a disrupted microbiota compared to healthy individuals, leading to impaired intestinal barrier integrity and activation of local inflammatory pathways. Increasing evidence also suggests that the gut microbiota of athletes differs from that of physically inactive individuals, showing greater microbial diversity and higher concentrations of short-chain fatty acids (SCFAs). In this context, the present clinical study aims to characterize the bacterial metagenome of the gut microbiota across a continuum ranging from inactive individuals to elite athletes with high or very high energy demands. The ultimate goal of this project is to determine whether specific gut microbiota composition and functional profiles are associated with different levels of exercise capacity, and to create a fecal microbiota biobank for future research on intestinal health.

Inclusion Criteria: * Male participant * Aged between 18 and 30 years (inclusive) * Body Mass Index (BMI) between 18 and 25 kg/m² (inclusive) * No history of gastrointestinal disease, including inflammatory bowel disease * Be a non-smoker. * Have a regular bowel transit (1-2 bowel movements per day or every other day) without recurrent episodes of diarrhea or constipation * Having provided free, informed, and written consent to participate in the study * Training status : * Low to moderate active subjects : Perform 2 to 4 hours per week of moderate to vigorous physical activity (VO₂max between 40 and 50 mL·min-¹·kg-¹). * Trained subjects : Perform 5 to 7 hours per week of regular endurance training for at least one year (VO₂max between 50 and 65 mL·min-¹·kg-¹). Highly trained subjects : Perform at least 10 hours per week of structured endurance training, with daily or twice-daily sessions (VO₂max greater than 65 mL·min-¹·kg-¹). Exclusion Criteria: * History of cardiovascular disease. * Presence of a metabolic disorder (e.g., diabetes). * Use of antibiotics, antifungal, or antiparasitic agents within the past 3 months, or planned use during participation in the study. * Use of prebiotic and/or probiotic supplements within the 7 days preceding the study, providing ≥10⁸ CFU or organisms per day. * Current use of medication for chronic pain management, including paracetamol, vasodilators, homeopathic treatments, or aspirin at doses \>500 mg/day. * Simultaneous participation in another clinical study involving human subjects, or recent participation in a previous study for which the exclusion period has not yet expired.