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Brain – Gut Axis


The impact of the gut microbiota on our physical and mental health


The microbiota is the set of microorganisms (bacteria, fungi, archaea, viruses, and parasites) present in the mucous membranes, respiratory tract, digestive tract, vagina, and skin. Of all of them, the most complex, diverse, and numerous is the one associated with the digestive system, particularly a part called blind, where the density of microorganisms is the largest in our body.

The microbiome refers to the entire habitat, including microorganisms, their genes, and environmental conditions. It is generally referred to as the genomic content of a microbiota.



It is the set of microorganisms that inhabit the intestinal tract and that can interact as diners (beneficial), mutualists, and also as pathogens (i.e. they cause some disease). Our gut is home to more than one hundred billion microorganisms, between 400 and 1500 species that are involved in digestion and defense functions of the gastrointestinal tract and may also be involved in mental health.

The composition of our gut microbiota is unique, in the image of our fingerprints. It defines and differentiates us by giving rise to a complex ecosystem, our organism.

The composition of the microbiota is greatly influenced by external factors, including birth conditions, diet, environment, individual habits, drugs (especially the use of antibiotics).

A healthy microbiota has great wealth and diversity of species, with stability over time, and is resistant, for example, to antibiotic treatments or unbalanced diets.

Certain external factors can have an impact on our gut microbiota. While some are difficult to control (genetics. mode of birth, geography, age, etc.), we can adapt others such as our diet and lifestyle to improve the functioning of our gut microbiota.

Digestive conditions, obesity, diabetes, allergies, cancer, and even neurodegenerative diseases can be associated with an imbalance in the composition or function of the gut microbiota (intestinal dysbiosis).

The functions of the gut microbiota are multiple and, therefore, researchers currently regard it as an “organ”:

  • Defense. It regulates the immune response of the organism, defending us from harmful microorganisms It teaches the immune system to distinguish between friends and enemies. It degrades toxins. It is estimated that 80% of immune cells are in the intestinal mucosa. A healthy and balanced microbiota reinforces the intestinal barrier by regulating the entry of molecules and organisms into our body.
  • Nutrition It allows the digestion of certain foods (such as food fibers) that man cannot digest. It breaks down food fibers by producing short-chain fatty acids that help regulate intestinal inflammation and the body’s exacerbated response. Facilitates the absorption of minerals (magnesium, calcium and iron). Synthesizes certain essential vitamins (vitamin K and folate [[B9]]) and amino acids (i.e. the foods that makeup proteins). A balanced microbiota facilitates the digestion of food, its transformation into energy and the elimination of excesses. Its imbalance is a marker in the source of discomfort and different diseases.
  • Behavior It can influence mood and behavior Our gut microbiota is known as our “second brain” because it houses the enteric nervous system (SNE) charged with “controlling” directly to the digestive system. The intestine is made up of one hundred million neurons, one-thousand of the neurons the brain has and as many as the spinal cord has. 50% of the dopamine and 95% of the Serotonin we produce originates in the gut; the microbiota is also involved in the release of GABA. These substances act directly and indirectly in behavior modulation, are related to well-being and good mood and are indicators of improvement in depression and anxiety.



This existence of the brain-intestinal axis connecting the central nervous system (brain and spinal cord), the autonomous nervous system (SNA) and the enteric nervous system (SNE) with the gut microbiota through the vagus nerve, the systemic pathway (by releasing hormones, metabolites and neurotransmitters) and the immune system (by the action of cytokines) has recently been described. Thus, in addition to diseases that have been classically linked to alterations in the microbiota such as obesity, type 2 diabetes, inflammatory bowel diseases and allergies, other central nervous system pathologies such as Parkinson’s disease, Alzheimer’s disease, ADHD, ADHD (anorexia nervosa) autism, anxiety and depression have also been linked lately.

The gut microbiota is decisive for maintaining the intestinal health and health of the body in general. Hippocrates (460-360 bc) noted that “all diseases begin in the intestine” A quantitative and qualitative study allows individual diagnosis of the patient’s dysbiosis. To do this, functional marker tests are requested, which together with the patient’s examination and medical history will be made the assessment to be able to propose the most appropriate and personalized therapy.

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