"All disease starts with the nerves" — a phrase many of us grew up with. And it has a solid scientific basis: there is a constant two-way connection between the gut and the brain. They exchange signals and affect each other's work — from mood to immunity.
How the gut–brain axis works
It is a two-way connection between the gut and the central nervous system. Signals travel along nerve pathways, including the vagus nerve, as well as through hormones, immune mediators and metabolites of the gut microbiota.
The microbiota is an essential participant in this axis. It takes part in metabolism, the regulation of immune responses and the maintenance of the intestinal barrier. When the bacterial balance is healthy, signals flow smoothly in both directions; when it is not, both digestion and mood suffer.
A little history: from "nervous sympathy" to the "second brain"
- 18th century. The Scottish physician Robert Whytt proposed the concept of "nervous sympathy". He suggested that the internal organs are connected by a shared system of nervous interactions.
- 1833. The physician William Beaumont studied a patient who was left with an opening in the stomach after a gunshot wound. Beaumont noticed that the patient's emotional state — including irritation and anger — was accompanied by changes in gastric secretion and digestion.
- 1998. The gut received the popular name "the second brain" after the publication of "The Second Brain" by the neurogastroenterologist Michael Gershon.
Serotonin and kynurenine: the "happiness hormone" and its dark twin
In chronic dysbiosis, the absorption of serotonin in the gut is impaired. Instead, the "unhappiness hormone" — kynurenine — begins to form. It can cause long-lasting depression.
Kynurenine affects the mitochondria of neuronal tissue and triggers the development of mitochondrial dysfunction. Kynurenine derivatives — for example, kynurenic and quinolinic acids — are neuroactive substances. Their imbalance is linked to the pathogenesis of depressive disorders and neurodegenerative diseases.
What this means in practice
Gut health is not only about digestion. It is about energy, resilience to stress and mood. Here are a few gentle steps to start caring for the gut–brain axis:
- Fibre and variety. Vegetables, greens, berries and legumes are food for beneficial bacteria. The more varied the diet, the more resilient the microbiota.
- Fermented foods. Sauerkraut, kefir, kombucha — in small amounts and without fanaticism.
- Routine. Regular meals and good sleep support both the gut and the nervous system.
- Movement and breathing. Walks and gentle breathing practices lower stress levels — and stress directly affects gut motility.
This material is educational and is not a medical recommendation. If you experience persistent digestive problems, anxiety or depressive states, please consult a doctor — the causes should be explored together with a specialist.
