Our bodies are home to over a thousand microscopic species which live together with our cells and, more often than not, enable them to function properly. We have twice as many bacteria as we do cells and the genes that they contain are a hundred times greater than our own genome. The organ with the greatest population is the intestine, followed by the skin.
This set of non-pathogenic* bacteria, viruses, parasites and fungi constitute our intestinal microbiota (or intestinal flora).
Following millions of years of joint evolution, our cells and bacteria have learnt how to help each other and secrete common molecules.Along with our epithelial cells**, all our bacteria secrete anti-microbial peptides*** which fight against the installation of pathogenic bacteria and the diseases associated with them.
On the other hand, our microbiota has learnt how to copy our own human molecules and is able to release growth factors for our cells into the intestine, but also neurotransmitters**** and cytokines***** which will enable them to influence our immune system and even our nervous system.
In a state of equilibrium, our microbiota promote digestion and immunity, and give advance warning of some diseases. They participate in the construction of the intestinal wall. But also influence our state of mind (their influence on depressive states is being studied in greater depth). Their influence on the condition of our skin through our nervous state, but also their control of the low-grade inflammatory state often at the origin of inflammatory component skin conditions (atopic dermatitis, acne, rosacea) is also being proven to a greater extent by scientists.
Each one of us has a different intestinal flora. Our intestine is sterile at birth and goes on to be colonised during our early childhood. As such, right from early childhood, food is primordial in creating diversified, balanced microbiota. Their composition is dependent on numerous factors such as dietary diversification, genetics, gender, standard of hygiene, medical treatments received (particularly antibiotics) and the environment. Their composition evolves both qualitatively and quantitatively during the first years of life and goes on to remain relatively stable in adulthood. With age, however, they become depleted and unbalanced.
The depletion of trace elements from the intensive cultivation of fruit and vegetables, the use of preservatives in processed foods, and hygiene measures that have drastically reduced the number of bacteria in our environment have all, little by little, contributed to the depletion of our intestinal microbiota. Microbial biodiversity is greatly reduced and enables colonisation by pathogenic bacteria (dysbiosis) and the onset of associated diseases.
* Pathogen: microbial organism that may lead to a disease
** Epithelial cells: cells comprising the intestinal wall, among others
*** Peptides: short molecules composed of several amino acids
**** Neurotransmitters: molecules released by the nervous system in order to transmit information between the nerves or between a nerve and a cell. Neurotransmitters also enable cells to communicate with each other.
***** Cytokines: molecules secreted by cells in order to regulate inflammation