In the recent years, many scientific discoveries have shown the importance of our intestinal flora and its impact on our health. The gut has been called the second brain, as it has many interactions with our different organs and is essential to our health.
What is the intestinal flora?
Bacteria are living microorganisms found everywhere in nature. We know well the pathogenic bacteria which are the ones leading to infections. We know less about those we call "commensal" that inhabit our skin and our mucous membranes, living in symbiosis with our body.
These groups of bacteria are not pathogenic, they are not leading to infections. They are beneficial, helping our bodies to function better in many ways. Associated with other microorganisms, they form colonies called microbiota. There are different microbiota in the body : oral-dental - cutaneous - vaginal, and intestinal. The intestinal microbiota lives in the small intestine and colon. (1)
What are the microorganisms that compose the intestinal microbiota?
The intestinal microbiota included more than 10,000 billion microorganisms (It is more than the number of cells in the human body), mostly bacteria, but also yeasts and parasites. The population of bacteria in the microbiota is very diverse. There are 800 to 1,000 different species of bacteria that can potentially live in our intestines, with at least 160 different species that can live within an individual.
Bacteria corresponds to 90% of this intestinal flora. So far, we have only been able to identify bacteria that can be cultivated in laboratory. These bacteria are divided into 4 major groups : Bacteroides, Eubacterium, Ruminococcus, Clostridium and Bifidobacterium. These bacteria interact directly with our bodies and are extremely beneficial to our health.
Yeast, virus and parasites such as candida, cryptococcus or Saccharomyces are also present in the intestinal flora. These organisms are significantly less than bacteria in number, and do not seem to have the same beneficial interaction with our body. However, if their number increases, they can be responsible for various symptoms and even infections, especially for immune-depressed patients. (2)
There is a great diversity in the makeup of these species from one person microbiota to another. While comparing microbiota from different persons from the same family, researchers found that only half of the species of bacteria from one family member’s microbiota was found in another family member’s microbiota. (1, 3) This diversity is even greater within populations, and between different populations worldwide. Our microbiome is unique for each of us, like our fingerprints. This diversity in microbiota explain why people can have a different relationship with diet and foods, why some are less sensitive to food than others and why we all have our unique way of eating healthy.
How is our microbiome formed?
The microbiome is unique to everyone and is defined at birth and in the first 3 years of life. The first contact we have with bacteria is around the time of birth, either with the mother's vagina bacteria or with the environment during C- section. This first contact greatly defines the type of microbiome we will have. After birth, bacterial colonization gradually increases, influenced by genetics, food diversification, and medications.
After the age of 3, the intestinal flora is relatively stable, but it can be altered by antibiotics, diseases, hormonal fluctuations, stress or changes in diet. When the harmful environmental factors stop, e.g. the end of an antibiotic treatment, the intestinal flora has the capacity to repair itself and regain its initial composition.
But sometimes, some alterations persist, and in the long term, lead to a permanent microbiota imbalance, called dysbiosis. This dysbiosis increases the risk of occurrence of some medical conditions. Everyone is not equal in front of dysbiosis, some intestinal floras are more stable than others and less prone to alteration. (4)
Why are these bacteria so beneficial?
The microbiota feeds on what we eat, and by doing so, it ferments and eliminates all the undigested residues that come in our intestines. These bacteria are also essential for the proper absorption of nutrients and essential fatty acids. Finally, they participate in the synthesis of certain vitamins and hormones. (5)
There are two kinds of bacteria in the intestinal flora, beneficial and harmful. In healthy subjects, the gut is well balanced and beneficial bacteria dominate.
Beneficial bacteria are producing molecules. Some of these molecules are absorbed by the intestine and are responsible for interacting with various organs. Other molecules interact with membranes to form an intestinal barrier, preventing toxins and outside organisms from entering the blood. (6)
Harmful bacteria, on the other hand, produce toxins and carcinogens. When the microbiota is balanced, these substances are easily eliminated by healthy bacteria. But when there is an imbalance between the 2 populations, these substances are in excess, creating inflammation and increasing the risks of different pathologies. An imbalanced intestinal flora has been associated with an increased risk of cancer, liver and kidney disease, high blood pressure, arteriosclerosis, and reduced immunity.
How to strengthen our intestinal flora?
A healthy, balanced diet rich in fibre is essential to strengthen our intestinal flora. Gut bacteria feed primarily on soluble fibre, mainly found in fruits and vegetables, and insoluble fibre, found in legumes and seeds.
When the imbalance is too important, a healthy and balanced diet might not be enough to correct this imbalance. Probiotics and prebiotics can be added then to help regrow a healthy intestinal flora. We can now test the intestinal flora and give probiotics adapted to the deficiencies found.
While dealing with an unhealthy gut, it is necessary to approach things holistically, taking into account the physical, emotional, and psychosomatic aspects that influence our microbiota's health. Stress management, exercise and improving our lifestyle also have very beneficial effects on the microbiota in the long term.
A healthy intestinal flora is essential for good long-term health. There are still many unknowns around this flora, its composition, and its interaction with our body, which seems very complex. Many studies are underway to understand better what affects this flora and how it affects and helps us.
2. The emerging world of the fungal microbiome Gary B. Huffnagle1 and Mairi C. Noverr2
1Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA, 2Department of Prosthodontics, Center of Excellence in Oral Biology, Louisiana State University Health Science Center School of Dentistry, New Orleans, LA, USA
Trends Microbiol. 2013 July ; 21(7): 334–341. doi:10.1016/j.tim.2013.04.002.
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5. Mitsuoka T. Intestinal flora and human health. Asia Pac J Clin Nutr. 1996 Mar;5(1):2-9. PMID: 24394457.
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