The intestinal microbiota it is the set of microorganisms (bacteria, fungi, viruses) that are symbionts that coexist with us, living in our intestines. This massive presence (we are even talking about 1.5 kg!) is not harmful to us, on the contrary: it is an example of mutualismwhere both parties benefit from mutual interdependence. In fact, these microorganisms perform essential functions for our health, from digestion to our mood. This complex balance begins to form at birth and develops through interactions with the environment such as diet, reminding us that, ecologically, we are not isolated individuals but part of a system that is both microscopic and immense.
The intestinal microbiota is the set of microorganisms present in our intestine
Let’s start with a little clarity: microbiota and microbiome are not synonymous. When we use the term microbiota we are referring to the set of living microorganisms, whereas when we talk about the microbiome we are referring to the set of genetic material contained in these organisms. The intestinal microbiota is made up not only of a bacteriotathat is, the set of actual bacteria that reside in our intestine, but also by a virota and a mycota, respectively made up of viruses and fungi residing in the intestine. The term bacterial flora instead, although not entirely incorrect, it refers to a dated classification of bacteria, which still included them among plants and in general it would be better to use the term microbiota.
In adulthood and for most of life, it weighs up to one and a half kilos of our body weight and is made up of two parts: a stable onewhich represents approximately 40% of the species and plays fundamental and difficult to replace roles, e a variablewhich makes up the remaining 60%, performs secondary functions and is more influenced by diet and habits. The delicate balance that balances the functions and abundance of microbial species will be changed again towards late ageleading in fact to greater risks of intestinal pathologies.
How the microbiota is born and how it arrives in our intestine
Having established the importance of terminology, let’s get to the heart of the matter by addressing a fundamental question: how do these bacteria get into our digestive tract? Initially it was believed that in the neonatal phase the human being was essentially sterile and that, therefore, the contamination necessary to obtain an intestinal microbiota occurred at the moment of birth and in the first subsequent moments, such as breastfeeding. Today neonatal sterility is taken less for granted, thanks to new studies that would suggest the presence of maternal bacteria in fetuses: at the moment there is no broad scientific consensus regarding pre-natal sterility.
However, it remains certain that the passage from the maternal vaginal canal and breastfeeding are crucial moments for the formation of the microbiota of the unborn child. Even i born by cesarean sectionand therefore not exposed to maternal contamination via the vagina, it would seem exposed to greater risk to contract intestinal diseases and allergies. Immediately after birth, our intestinal microbiota is still in a phase of great change and maturation, and is therefore particularly susceptible to diet and environmental exposure.
Its functions and impact on health
Thanks to genetic sequencingthe study of the microbiome allows us to identify the species present in the microbiota and to analyze fundamental aspects, such as the diversity of species, their relative abundance and the relationship between beneficial and potentially harmful species. However, it is important to understand that the microbiota does not act independently of our organism: its properties derive frominteraction between bacterial products and human metabolism. As a result, it is not possible to determine whether a species is beneficial or not without considering factors such as its abundance, its location and the state of health of the host.
The analysis of the microbial population of our intestine has revealed that the most common and most important intestinal bacteria in the entire world population belong to the genera of Bacteroides, Prevotella and Ruminococcus. The species diversity of our intestinal microbiota performs a number of functions, of which some are essential for our survival.
Among the most important we find the production of vitamins such as K and B12, the synthesis of amino acids and short-chain fatty acids, and the control of cell proliferation. Furthermore, some bacteria seem to keep the body trained immune system to identify abnormal or foreign cells and eliminate them. The microbiota then carries out protective functions, thanks to the ability to fight infections from microorganisms that are harmful to themselves and to us who host them.
However, the effects of the intestinal microbiota extend beyond the intestine, influencing organs and systems such as the liver, the nervous system, the cardiovascular system e the endocrine-metabolic system. The microbiota can influence the liver through substances absorbed from the intestine, which in case of imbalances can cause steatosis or inflammation. We are recently investigating the relationship between intestinal microbiota and the central nervous system. We are discovering that the microbiota is able to influence the tone ofhumor and some behaviors: not surprisingly, we often hear about the intestine as the “second brain”.
Finally, the microbiota can contribute to the control of cardiovascular risk factors such as hyperlipidemia, type 2 diabetes and atherosclerosis, it is also able to alter the outcome of therapies for pathologies such as depression and cancer, thus confirming itself as an element of primary interest in medicine, even in apparently distant fields of human health.
