The intestinal microbiota: why I take care of it

What if my intestine was much more than just a digestive organ?

My intestine is home to approximately 100,000 billion microorganisms - bacteria, viruses, fungi, parasites - forming an ecosystem of remarkable complexity: the intestinal microbiota. This dizzying figure represents 10 times more microbial cells than human cells in my body. In recent years, scientific research has transformed our understanding of this invisible organ, to the point that some researchers now call it the second brain. Here's what science knows today, and why taking care of my microbiome is one of the smartest investments in my overall health.

1. What is the intestinal microbiota?

The intestinal microbiota refers to all the microorganisms that colonize the digestive tract, mainly the colon. It represents a total mass of approximately 1 to 2 kg in adults and contains more than 1,000 different bacterial species, the majority of which are beneficial to us.

Each individual has a unique microbiota, comparable to a fingerprint. Its composition is influenced by:

• ●Method of birth (vaginal delivery vs cesarean section) and breastfeeding in the first months of life

• ●Nutrition throughout life - the most flexible factor in adulthood

• ●Use of antibiotics and other medications

• ●Chronic stress level

• ●The geographical environment and lifestyle habits

• ●Regular physical activity

We speak of dysbiosis when the balance of the microbiota is disturbed - reduction of bacterial diversity, proliferation of pathogenic bacteria, reduction of beneficial species. Dysbiosis is today associated with numerous chronic pathologies.

Function	What the microbiota actually does
Digestion and absorption	Fermentation of dietary fiber, production of acids short-chain fat (SCFA), synthesis of certain vitamins (K, B12, B9) 13px;border:1px solid #B2DFDB;color:#374151;vertical-align:top;background:#F4FBFA">70% of immune cells are found in the intestine. The microbiota trains and regulates the immune system, protected against pathogens
Gut-brain axis	Production of 90% of the body's serotonin. Bidirectional communication with the brain via the vagus nerve, influence on mood and behavior 13px;border:1px solid #B2DFDB;color:#374151;vertical-align:top;background:#F4FBFA">Regulation of fat storage, insulin sensitivity and appetite via hormonal signals
Protection of the intestinal barrier	Maintenance of the integrity of the intestinal mucosa, prevention of leaky gut syndrome gut)
Regulation of inflammation	Production of anti-inflammatory molecules (butyrate in particular) and modulation of the systemic inflammatory response

2. The key functions of the microbiota: much more than digestion

Long considered a simple aid to digestion, the intestinal microbiota is today recognized as a major player in overall health, involved in very diverse biological processes:

3. The link between microbiota and chronic pathologies

One of the most spectacular advances in microbiology research is the demonstration of links between dysbiosis and numerous chronic pathologies. These associations, documented in hundreds of studies published in the best scientific journals, do not always mean causality - research is still underway to disentangle cause and consequence - but they open up considerable therapeutic perspectives.

• ●Obesity and metabolic syndrome: studies on germ-free mice (raised without microbiota) showed that the transfer of microbiota from obese mice to these mice caused weight gain, suggesting a causal role of the microbiota in obesity (Nature, 2006).

• ●Type 2 diabetes: specific dysbiosis is associated with an increase in intestinal permeability and metabolic endotoxemia, promoting insulin resistance (Diabetologia, 2012).

• ●Inflammatory bowel diseases (IBD): Crohn's disease and ulcerative colitis are characterized by profound dysbiosis and an aberrant immune response to the microbiota.

• ●Mental health: the microbiota-gut-brain axis is involved in depression and anxiety. A meta-analysis published in General Psychiatry (2019) showed that probiotic supplementation reduced depressive symptoms.- Colorectal cancers: certain bacterial species (especially Fusobacterium nucleatum) are over-represented in colorectal tumors, suggesting a role for the microbiota in digestive carcinogenesis.

4. What disrupts my microbiota on a daily basis

Several elements of the contemporary lifestyle constitute direct threats to the diversity and balance of the microbiota:

• ●Antibiotics: antibiotic treatment can eliminate up to a third of bacterial species from the microbiota. Recovery takes on average 1 to 2 months, but some species may never fully return. This does not mean that we should avoid antibiotics when they are necessary, but understanding their impact helps us use them better.

• ●Ultra-processed food: food additives (emulsifiers, preservatives, artificial sweeteners) significantly disrupt the composition of the microbiota according to several recent studies, including one published in Nature (2022).

• ●Lack of fiber: beneficial bacteria feed mainly on dietary fiber. A diet low in fiber leads to a progressive depletion of the microbiota.

• ●Chronic stress: via the hypothalamic-pituitary-adrenal axis, stress disrupts intestinal motility and modifies the composition of the microbiota.

• ●Lack of sleep: a study published in Sleep Medicine (2019) showed that sleep deprivation modified the composition of the microbiota in a similar way to an imbalanced diet.

5. How to nourish and diversify my microbiota

The good news: the microbiota is one of the most plastic organs in the body. Its composition can change significantly within a few days in response to dietary changes. Here are the most documented levers:

• ●Increase prebiotic fibers: prebiotic fibers selectively feed beneficial bacteria. The best sources are garlic, onion, leek, Jerusalem artichokes, green bananas, asparagus, legumes and whole grains. Objective recommended by ANSES: 25 to 30 g of fiber per day.

• ●Consume fermented foods: natural yogurt, kefir, raw sauerkraut, kimchi, miso, tempeh. These foods contain live probiotics that temporarily enrich the microbiota. A study published in Cell (2021) by Justin Sonnenburg's team showed that a diet rich in fermented foods increased the diversity of the microbiota more effectively than a diet rich in fiber alone.

• ●Diversify my plant-based diet: bacterial diversity is directly correlated to dietary diversity. The objective of 30 different plants per week, proposed by the American Gut project, is associated with a more diverse and more resilient microbiota.

• ●Avoid unnecessary antibiotics: discuss alternatives with my doctor when possible, and always accompany antibiotic treatment with probiotic supplementation and a diet rich in fiber.

• ●Practice regular physical activity: several studies show that regular physical exercise independently promotes the diversity of the microbiota, in particular via the production of short-chain fatty acids.

  💡 tips to remember

  1. My microbiota weighs 1 to 2 kg and contains more than 1,000 bacterial species: it is an organ in its own right which influences my digestion, my immunity, my mood and my metabolism.
  2. 70% of my immune cells are found in my intestine: taking care of my microbiota directly strengthens my natural defenses.
  3. I aim for 25 to 30 g of fiber per day: they nourish beneficial bacteria and promote the production of butyrate, a protective anti-inflammatory fatty acid.
  4. I consume fermented foods regularly: natural yogurt, kefir, raw sauerkraut, kimchi. They provide live probiotics which enrich my microbiota.
  5. I aim for plant diversity: 30 different plants per week is the objective associated with the most diverse and resilient microbiota.
  6. Antibiotics, when necessary, eliminate up to a third of bacterial species: I always accompany them with probiotics and a diet rich in fiber.
  7. The microbiota is plastic: its composition can change significantly in a few days with dietary changes. It's never too late to do the right thing.