Part 1: General Information
1. What is the microbiota?
The microbiota defines a community of microorganisms colonizing the human body. Humans have co-evolved with microbes in the environment, and each bodily habitat has a unique set of microorganisms in its microbiota. The total microbiota present in the human body is composed of more than 38 trillion cells, or 0.3% of the total body weight 1. The largest concentrations of microbes occupy the gut, skin, and oral cavity, and among the different microbiotas, the gastrointestinal tract contains the most microorganisms in terms of both number and species 1. Indeed, the gut microbiota is composed of more than a thousand species of microorganisms, such as viruses, bacteria, and fungi 3. First identified as disease vectors during the 20th century ⁷⁻⁸, it is now established that certain microorganisms are not only commensal, that is to say they colonize the organism without causing harm, but above all symbiotic with their host: they are beneficial to the proper functioning of the body ⁹.
2. What is the role of the microbiota?
At the intestinal level, the microbiota is involved in a large number of functions essential to the proper functioning of the body. It is thus involved in major essential functions such as nutrition, development, immunity and well-being ¹⁰ ⁻¹² . The intestinal microbiota is essential for the breakdown of food, the synthesis of vitamins and biomolecules useful to the body, the absorption of fatty acids, calcium and magnesium ⁶ ¹³ , but also for the proper functioning of the immune defenses, the major systems that govern the human body, etc.
3. How does the microbiota evolve over the course of a lifetime?
Each individual has a distinct and unique population of microorganisms in their environment 1⁴ , even if we have strains in common between individuals. Furthermore, the microbiota is not constant over the course of a lifetime; its composition actually fluctuates significantly with age and in response to certain changes (dietary, health, behavioral, etc.). The intestinal flora is constantly exposed to different elements that can change its composition, whether it be diet, ingested medications such as antibiotics, or disease-carrying pathogens, for example. A change in our lifestyle can lead to changes in the intestinal microbiota, as has been established in the case of physical activity 1⁵ . The influence of lifestyle on the intestinal microbiota is therefore well established and important. Comparing the microbiota of populations in industrialized countries with that of contemporary populations still living traditionally highlights a different functional role of the microbiota between these two types of population. For example, the microbiota will no longer degrade the same ingested elements, the functional modification of the activity of the microbiota appearing to be linked to a loss of diversity of bacterial species ¹⁶ ¹⁷.
4. What are the risk factors for an unbalanced microbiota?
The reason we focus so much on the importance of a healthy microbiota is that its composition can be impaired, and we observe an imbalance in its composition of microorganisms: an increase in pathogenic strains and/or a decrease in beneficial strains. When this imbalance is too significant, we speak of dysbiosis. This alteration of the intestinal flora can have minimal consequences, such as mild intestinal problems, but also much more significant health concerns: in fact, research is finding more and more compromising links between dysbiosis and obesity ¹⁸ , hypertension ¹⁹ , depression ²⁰ , etc.
The underlying mechanisms and manifestations of dysbiosis remain unclear: the risk factors and consequences of this condition are numerous. Among the main risk factors are stress, certain inflammatory diseases, certain metabolic disorders and certain drug treatments ² ¹ .
A genetic factor is also to be taken into account in the etiology of dysbiosis. But one of the most important factors remains diet, and sudden changes in diet. Indeed, the largely industrialized diet that we know today has a large part of responsibility in the appearance of dysbiosis: preservatives, additives, endocrine disruptors, pesticides, unreasonable macronutrient intakes... All these factors have an influence on the constitution of our intestinal microbiota. Finally, alcohol and tobacco are once again significant risk factors ²² ,²³ .
But one of the reasons that can jeopardize the composition of a child's gut microbiota throughout their life is poor development during childhood. Indeed, good habits must be adopted if you want your child to benefit from an optimal microbiota in the future.
Part 2: The importance of childhood in the formation of the microbiota
1. How do humans build their microbiota?
From the first seconds of life, we shape our different microbiotas. Indeed, we come into contact with surrounding microorganisms from birth. In vaginal delivery, for example, newborns encounter all types of microorganisms in their mother's vagina, and in contact with the hospital environment: this is the first stage in the formation of the microbiota. Studies have also highlighted a link between the composition of the intestinal flora and the method/place of delivery, which subsequently impacts the risk of atopic manifestations ²⁴ . Other factors come into play during birth to facilitate the proper constitution of the child's microbiota, in particular contact with the parents' skin and breastfeeding, which allows the transmission of some probiotic bacteria. Breast milk also contains some fibers with prebiotic effects. But it is important to ensure that good habits are multiplied throughout childhood. These include, for example, exposure to pets, which allow the child to come into contact with a multitude of new microorganisms and strengthen their intestinal flora. Research has also highlighted the importance of limiting the administration of antibiotics, that is, limiting their use to when it is really necessary ²⁵ .
Once again, diet plays a key role. From birth, the way a child is fed will have an impact on the composition of their gut flora. Researchers agree that breastfeeding will have a beneficial impact on their microbiota, compared to formula feeding ²⁶ .
A good, controlled and varied dietary diversification during childhood will allow each individual to build a solid intestinal microbiota.
Some studies tend to demonstrate that alterations in the child's intestinal microbiota could be linked to previous alterations in the maternal microbiota during, or even before, childbirth ²⁵ .
The major problem regarding children's microbiota remains the risk factors to which they are exposed. This greatly endangers the proper development of their microbiota, and weakens their resistance to future pathologies. One of the best indicators of this situation remains the increasing prevalence of certain pathologies. Indeed, allergies (cutaneous, respiratory, and generalized) affect 25-30% of the world's population. While this figure did not exceed 3% in 1970, it should be around 50% in 2050 according to the World Health Organization ³⁵ . Another telling figure concerns viral intestinal infections. In France, acute viral gastroenteritis is increasingly frequent and 90% of children under 2 years old have already been subject to it . The proper development of children's microbiota is slowed down these days and it is therefore wise to turn to solutions.
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