Each of these groups works together to maintain a symbiotic environment. If there's a problem in one group, the whole machine is affected. In microbiology, this is known as the Red Queen paradox.

So, briefly, how does it work?

When we ingest food, as it makes its way through the digestive tract, each group of bacteria recovers the nutrients it needs (such as fiber for certain groups) and passes on the rest to another group - a bit like in the film “The Platform”. From the recovered nutrients, each group will generate new molecules to feed other groups of bacteria. This is the cycle of feeding, development and growth of a balanced microbiota.

For example, the fiber we eat feeds certain types of intestinal bacteria, which in turn feed other bacteria with the new molecules generated. With a low-fiber diet, these first bacteria disappear, leaving the rest of the chain un nourished.

In this way, a natural food will travel through the entire digestive tract, feeding the entire chain, with the rest being expelled in the stool.

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There are nutrients essential to our health that our body produces little or none of, such as the 9 essential amino acids, which we obtain only through our diet and which the body uses for various needs.

These essential amino acids are found in natural foods: legumes, cereals (wheat, rice, corn), dried fruit, soya, eggs, fish, cheese, fruit and vegetables.

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I insist on the term “natural food” because ultra-processed industrial products are different.

Ultra-processed industrial products are not raw, solid foods full of nutrients. They are shaped, recomposed foods into which a whole set of chemicals is injected. Barely past the first stage of digestion, which is gastric acid (which normally helps the rest of the digestion process to hull the raw food), the processed food disintegrates and feeds only the first few intestinal bacteria with the few nutrients available. The majority of the digestive system is then not nourished.

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The brain is fooled because it sees that its body has been nourished and that it has felt its shot of energy and satiety, but the bacteria quickly die of hunger, so very quickly ask for more.

At each stage of its decline, the intestinal microbiota sends signals to the brain, with which it is in constant communication via the vagus nerve.

Beyond the impact on weight and deficiencies, this triggers a vicious circle in which the brain and the gut no longer understand each other, enter into conflict and then, in a state of emergency, survive - generating more serious pathologies.

And, as we have seen, when we feel unwell, the brain also sends biased signals to various cells, including those in the gut microbiota.