The term “gut-brain axis” refers to the interrelationship that exists between the gut microbiota and the brain. The gut microbiota is formed by the microorganisms that inhabit our gut, and includes billions of microbial cells including bacteria, viruses, fungi and other microorganisms. These microorganisms are capable of influencing not only the overall health of the host, but also behavior and cognitive function.
The composition of the diet modulates the composition of the microbiota and the production of its metabolites in the gut, most likely due to the prebiotic effect of fiber contained exclusively in plant foods. A diet rich in unprocessed plant foods has been shown to promote a greater variety and abundance of beneficial species due to its fiber and phytocompound content. In fact, compared to omnivores, vegetarians have a higher Prevotella / Bacteroides ratio and a lower Firmicutes / Bacteroidetes ratio.
In turn, the microbiota produces indispensable molecules such as vitamin K, short-chain fatty acids (SCFs) and other metabolites, including neuroactive molecules (such as serotonin, dopamine, butyric acid), which act as neurotransmitters. Since some of these molecules are able to influence the functioning of our brain, regulating cognitive function, behavior, and mood, the term gut-brain axis has been coined.
Alteration of the microbiota has been associated with the development of psychiatric disorders (major depression and bipolar disorder, schizophrenia, autism spectrum disorders, and attention deficit hyperactivity disorder), as well as neurodegenerative diseases: increased permeability of the gut barrier, with activation of the immune system and subsequent chronic inflammation, would in fact be responsible for neuroinflammation and neurodegeneration.
Therefore, a healthy microbiota represents an element that promotes optimal health, both physical and mental. The composition of the microbiota depends primarily-though not exclusively-on diet: therefore, deciding what to put on your plate can help prevent psychiatric and neurodegenerative diseases, which are increasingly common in Western civilizations.
