The gut-brain axis - how the digestive tract + intestinal bacteria influence our thinking

Die Darm-Hirn-Achse – So beeinflussen Verdauungstrakt + Darmbakterien unser Denken

Everyone knows this: when digestion works, we feel good. But a balanced intestine not only affects our physical well-being - the digestive system also has a decisive effect on a person's mental state. The connection is made up of the so-called intestinal-brain axis.


  1. The brain in the gut
  2. Digestion and emotions
  3. Abdominal brain and head brain
  4. Antidepressants for digestion?
  5. The importance of the intestinal flora
  6. The power of bacteria
  7. Psychobiotics

1. The brain in the gut

The intestine has its own nervous system: the so-called enteric nervous system (ENS) is a network of millions of nerve cells that runs through the intestinal wall. The ENS is independent of the central nervous system (CNS; brain and spinal cord) - this means that digestion takes place without us having to think about it.

However, the brain and intestines communicate with each other constantly: the mere thought of eating triggers the digestive process and makes our mouths water. Conversely, the digestive tract signals the brain when we have eaten enough and are full.

2. Digestion and emotions

Because of its huge number of nerve cells, the ENS is often referred to as the “second brain” or “gut brain”. The close connection between the ENS and the CNS is also reflected in our usage, for example when we speak of our “gut feeling”, “have butterflies in our stomach”, or “hit our stomach”.

Indeed, emotions affect our digestion: stress, reduces blood circulation and inhibits the production of digestive secretions. Accordingly, we lose our appetite when we are scared of exams.

3. Abdominal Brain and Head Brain

The ENS is not unlike the CNS: both systems have the same nerve cells and use the same neurotransmitters. While the "happiness hormone" serotonin in our brains affects how happy we feel, it regulates the rhythmic muscle contractions in the intestine that carry the food porridge through our intestines - the so-called peristalsis.

Communication between the intestine and the brain takes place via nerve pathways and messenger substances. The impulse can come from both the brain and the intestine. Mental problems can cause digestion to rebel and conversely, digestive problems can affect the psyche - this is becoming increasingly clear in research.

4. Antidepressants for digestion?

The close connection between abdominal brain and head-brain makes it possible to treat certain diseases of the digestive system with the same medication as psychological ailments. For example, irritable bowel patients can benefit from antidepressants that raise serotonin levels and thus not only boost mood, but also digestion.


5. The importance of the intestinal flora

The already complex interplay between intestine and brain is far more complicated. Our intestines are home to trillions of bacteria. The community of microorganisms - including viruses, fungi and yeasts - is called the intestinal flora or the microbiome.

Anyone who automatically thinks of harmful pathogens when talking about “bacteria” is wrong. The bacteria in our intestines are vital for us. They support our digestion, activate our immune system, extract macro and micronutrients, produce vitamins, fatty acids, hormones and neurotransmitters.

The microbiome consists of about 85% percent of “good” intestinal bacteria. Our environment, nutrition, medication (especially antibiotics) or stress influence which bacteria colonize our intestines. If the ratio of "good" and "bad" bacteria gets out of balance, indigestion or inflammation of the intestinal mucosa can occur, which often lead to further diseases.

6. The power of bacteria

Research is just beginning when it comes to the impact of our gut bacteria on our brain. In a large number of studies, there is an interplay between psychological problems such as depression or anxiety and improper colonization of the intestine.

For example, irritable bowel patients often suffer from psychological problems or depressed people have to struggle with digestion. The exact connection and interactions between the diseases has not yet been clarified.

Fascinating studies with mice, however, indicate the power of the microbiome: mice that showed signs of autism became more social and less anxious when given certain probiotic bacteria. Conversely, after the microbiome of depressed people was implanted, mice showed signs of depression.

7. Psychobiotics

While research on mice cannot be directly transferred to humans, studies with human subjects are also promising. Thus, the psyche of participants could be repeated by administering Probiotics  - especially of the genera lactobacteria and bifidobacteria - can be influenced positively.

For example, 64% of a group of irritable bowel sufferers suffering from anxiety disorders or depression reported improvement in their mental health problems after taking the probiotic Bifidobacterium longum for six weeks.Because of their effect on the human psyche, these types of Probiotics  referred to as psychobiotics.

The exact relationship between microbiome and mental health is still unclear. However, researchers agree that it is beneficial for us if as many different “good” bacteria as possible live in our intestines. We can control the diversity of bacteria by eating a healthy, varied diet, avoiding stress and taking Probiotics  support.

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  • Qinrui Li et al .: The Gut Microbiota and Autism Spectrum Disorders. Front Cell Neurosci. 2017; 11: 120.

  • Friedmann LS et al .: The Sensitive Gut. A Harvard Medical School Special Health Report, Harvard 2008.

  • Pinto-Sanchez MI et al .: Probiotic Bifidobacterium longum NCC3001 Reduces Depression Scores and Alters Brain Activity: A Pilot Study in Patients With Irritable Bowel Syndrome. Gastroenterology. 2017 Aug; 153 (2): 448-459.