What is the gut flora, and why is it essential?
The gut flora —a common term for the gut microbiota—refers to the 100,000 billion microorganisms (bacteria, archaea, viruses, and yeasts) that reside in our digestive tract, primarily in the colon. Its total weight is approximately 1.5 to 2 kg, and its genome (metagenome) contains 150 times more genes than the human genome. The microbiome is unique to each individual; it begins to form at birth and evolves throughout life. Probiotics and digestive supplements are available in the store.
- Key roles: digestion of indigestible dietary fiber (fermentation into short-chain fatty acids—butyrate, propionate, acetate—which nourish colonocytes)—synthesis of vitamins (K2, B9, B12, B8) — maturation and regulation of the immune system (70% of immune cells are located in the gut) — protection against pathogens through a barrier effect (competitive exclusion) — gut-brain axis (serotonin production—95% of the body’s serotonin is produced in the gut)
- Dysbiosis: imbalance of the microbiota — reduced bacterial diversity — increase in pro-inflammatory species — increased intestinal permeability (“leaky gut”) — associated with numerous conditions (inflammatory bowel diseases, obesity, metabolic syndrome, autoimmune diseases, anxiety and depression)
- Signs of imbalance: digestive issues (constipation, diarrhea, bloating, difficulty digesting food) — unexplained fatigue — increased sugar cravings — immune reactivity (recurrent infections, allergies) — effects on mood and concentration
- Gut-Brain Axis: the vagus nerve and gut neurotransmitters facilitate bidirectional communication — the microbiota directly influences mood, behavior, and the stress response — a depleted microbiota is associated with a higher prevalence of anxiety and depression
How can you maintain and improve your gut microbiota?
Dietary diversity is the key — a diverse microbiota is a resilient microbiota. Studies show that people who consume more than 30 different plant species per week have a significantly richer microbiota than those who consume fewer than 10. The Mediterranean diet—rich in vegetables, legumes, fruits, whole grains, olive oil, and fatty fish—is the best-documented dietary model for gut microbiota health.
- Prebiotics (fermentable fibers): inulin, FOS (fructo-oligosaccharides), GOS (galacto-oligosaccharides)—found in garlic, onions, leeks, asparagus, green bananas, legumes, and chicory—feed bifidobacteria and lactobacilli—promote butyrate production—see prebiotics
- Probiotics: live microorganisms (Lactobacillus, Bifidobacterium, Saccharomyces boulardii) found in fermented foods (yogurt, kefir, sauerkraut, kimchi, miso, tempeh) or supplements—effectiveness depends on the strain and specific use— probiotic supplements are available
- Healthy lifestyle: regular physical activity (increases microbiota diversity and butyrate production)—sufficient sleep (7 to 9 hours—the microbiota follows a circadian rhythm)—stress management (chronic cortisol alters the composition of the microbiota and increases intestinal permeability) — limiting antibiotic use to strictly necessary cases (antibiotic treatment can reduce microbiota diversity for 6 to 12 months)
- Disruptive factors to limit: alcohol — smoking — ultra-processed foods (emulsifiers, artificial sweeteners) — chronic stress — a sedentary lifestyle — excessive saturated fats
Microbiome, Immunity, Weight, and Age: What Are the Links?
- Microbiota and immunity: the microbiota modulates the Th1/Th2 axis — an imbalance toward an excessive Th2 response is associated with allergies — babies born vaginally and breastfed have a more diverse microbiome, which is correlated with a reduced risk of allergies and asthma — strengthening natural immunity depends on the health of the microbiome
- Microbiome and weight: certain bacterial strains (Firmicutes/Bacteroidetes ratio) influence calorie extraction from food and fat storage — short-chain fatty acids regulate satiety hormones (GLP-1, peptide YY)—a microbiome lacking in diversity is associated with an increased risk of obesity and metabolic syndrome
- Impact of age: An infant’s microbiome is established at birth (from the mother’s vaginal flora) and changes with the introduction of solid foods—in adulthood, it stabilizes—in older adults, diversity decreases with dietary changes, a sedentary lifestyle, and medication—maintaining a high-fiber diet and physical activity preserves diversity at any age
- Intestinal Permeability: Dysbiosis promotes mucosal hyperpermeability (impaired tight junctions)—entry of bacterial LPS (lipopolysaccharides) into the circulation—low-grade systemic inflammation—probiotics based on Lactobacillus and Bifidobacterium help restore the intestinal barrier
