How our digestive tract and gut bacteria influence our thinking and mood

By Roxana Voicu
September 5, 2022

The human intestine has its own nervous system, the enteric nervous system, a network of millions of neurons, which surrounds the entire intestine. Our digestion takes place without us thinking about it, the enteric nervous system functioning without conscious control. But the brain and the gut are in constant communication: the thought of food causes digestive enzymes to be secreted and leaves our mouths watering, for example. The gut also signals to the brain when we have eaten enough.

Because of the huge number of neurons, the enteric nervous system is also called the ‘second brain’ or the ‘emotional brain’. We have expressions such as ‘butterflies in the stomach’, ‘clenching the stomach (from a strong emotion)’ or ‘nervous eating’, all of which show the influence of emotions on digestion. Stress decreases blood flow to the gut and inhibits the production of digestive secretions. In the case of an exam we lose our appetite or, on the contrary, we eat „nervously” to compensate for stress.

Like the central nervous system, the enteric nervous system is made up of neurons and uses the same neurotransmitters. The happiness hormone, serotonin, regulates well-being, satisfaction and fulfilment in the brain, but it also plays a role in the gut, regulating contractions of the intestinal wall muscles and intestinal peristalsis. Communication between the gut and the brain is bidirectional. Mental problems can disrupt food processing and absorption, but the reverse is also true: digestive problems can influence mental state, which is increasingly evident in recent research. The similarities and communication between the two nervous systems, central and enteric, make it possible to treat certain functional digestive problems with drugs or therapies that address the psyche.

But the complex link between the gut and the brain is even more complicated and goes beyond neural networks and neurotransmitters. Our gut is colonised by billions of micro-organisms, including bacteria, viruses and fungi, known as the gut flora or gut microbiome. The bacteria present in the human gut are essential for our survival, supporting digestive functions, activating the immune system, extracting micro- and macronutrients, synthesising vitamins, fatty acids, hormones and neurotransmitters.

The gut microbiome is made up of about 85% ‘good’ bacteria. Environmental factors, diet, drugs (especially antibiotics) and stress all influence the type of bacteria that colonise us. When the balance between helpful and harmful bacteria is disturbed, it can lead to inflammation of the intestinal lining or digestive disorders, which in turn lead to other diseases (autoimmune, cardiovascular, inflammatory and degenerative joint, mental, cancer and others).

Research into the specific role of certain groups of bacteria on the brain is just beginning. Many studies link mental problems such as depression or anxiety to intestinal dysbacteriosis. Patients with an irritable bowel are known to suffer from depression or other mental disorders.

The exact causal correlations are not fully elucidated. The results of mouse studies are fascinating: autistic mice became more sociable and less fearful after taking certain probiotics. Also, a group of mice transplanted with microbiome from depressed patients showed signs of depression. While these correlations from mouse research cannot be extrapolated directly to humans, studies with human subjects are also promising. It has been shown in several studies that the mental state of depressed patients improves considerably after taking probiotics with lacto- and bifidobacteria. 64% of patients with irritable bowel, anxiety and depression included in one study improved their mental state after taking a probiotic preparation for 6 weeks.

Researchers agree that a wide variety of saprophytic (‘good’) gut bacteria is essential for the wellness that defines health. This can be achieved through a varied diet (rich in vegetables, fruit, whole grains containing fermentable fibre), reducing stress and supplementing with probiotics where appropriate.
Retrieved from: Die Darm Hirn_ Achse- So beeinflussen Verdauungstrakt+ Darmbakterien unser Denken 29.11.2019 (
Schlagen mir meine Darmprobleme auf die Psyche? 13.07.2018 Institut fuer Mikrooekologie in Herborn


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