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.

The gut microbiota includes all microorganisms-bacteria, viruses, and fungi-that inhabit the digestive tract. Colonization begins at birth and evolves throughout life under the influence of numerous factors such as diet, antibiotic use, sleep, stress, physical activity, exposure to environmental agents, as well as age, sex, and ethnic or migratory background.

This microbial ecosystem performs several essential functions for its host, including digestion and nutrient absorption, immune regulation, and protection against pathogens. Through the fermentation of complex carbohydrates, particularly dietary fibers indigestible by human enzymes, certain bacteria produce short-chain fatty acids (SCFAs), mainly butyrate, propionate, and acetate. These metabolites play a key role in maintaining intestinal barrier integrity and in the energy metabolism of colonocytes.

When microbial composition or function is altered, whether in diversity, relative proportions, or metabolic pathways, a state of dysbiosis occurs. This imbalance is frequently observed in various pathological conditions and has been associated with the development of diseases such as diabetes, certain cancers, atherosclerosis, asthma, inflammatory bowel diseases (IBD), and even depression.

IBD encompasses Crohn's disease (CD) and ulcerative colitis (UC). While CD is characterized by discontinuous lesions throughout the gastrointestinal tract, UC involves continuous and superficial inflammation of the colon. These pathologies affect 0.3-0.5% of the global population. Numerous studies have demonstrated significant differences in microbiota composition between IBD patients and healthy individuals, leading to impaired intestinal barrier function.

In parallel, a growing body of evidence suggests that the gut microbiota of physically active individuals differs from that of sedentary people.

More recently, our laboratory characterized the gut microbiota of 50 volunteers ranging from inactive individuals to elite athletes with high (elite football players) and very high (elite cyclists) exercise capacities. Our data revealed that exercise capacity influences gut microbial ecology and fecal SCFA levels, independently of diet. Interestingly, individuals with very high exercise capacity displayed reduced microbial diversity, density, and functional pathway abundance, raising questions about whether such microbial ecosystems are beneficial for host energy metabolism and exercise performance. Using FMT from human donors in our cohort to antibiotic-treated mice, we further demonstrated that donor microbiota, linked to exercise capacity, affects insulin sensitivity and muscle glycogen storage in recipient mice, highlighting the critical role of exercise-associated gut microbiota in shaping host metabolic responses.

In this context, this clinical study aims to characterize the bacterial metagenome of the gut microbiota across a continuum ranging from sedentary individuals to elite athletes with high or very high energy demands, and to determine whether specific gut microbiota composition and functional profiles are associated with different levels of exercise capacity. The ultimate goal of this project is to create a fecal microbiota biobank for future research on intestinal health.

The MICROPEPS clinical protocol is a prospective, single-center, comparative, and minimally interventional study. No drug, medical device, or product will be tested within this protocol. The study will be conducted at the Exermove platform (M2S Laboratory) to evaluate exercise capacity and the metagenomic signature of the gut microbiota in active, trained, and highly trained endurance men. Participants will attend three laboratory visits:

1. Inclusion visit: anthropometric measurements, dietary and physical activity questionnaires. Participants will then receive a fecal collection kit to collect and send a stool sample within seven days.
2. Second visit: incremental cycling test to determine VO₂max.
3. Third visit: metabolic assessments under fasting conditions, at rest and during submaximal exercise.

Metabolic parameters measured during these tests (e.g., VO₂max, power output at aerobic and anaerobic thresholds, maximal carbohydrate and lipid oxidation) will be correlated with metagenomic shotgun data obtained from fecal samples.

Additionally, the study will establish a fecal microbiota biobank of donors stratified by exercise capacity. Using a mouse model of fecal microbiota transplantation combined with DSS-induced colitis, the final aim is to determine how donor exercise capacity and gut microbial ecosystems influence inflammatory responses and intestinal permeability

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.

Populations located in a continuum from inactive people to top-level athletes with high and very high exercise capacity.