Depression: This is how intestinal bacteria are related to mental disorders

Depression: This is how intestinal bacteria are related to mental disorders

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New insights: How gut bacteria make you depressed

Years ago, scientific studies provided evidence that intestinal bacteria can cause depression. Austrian researchers have now gained new insights into how gut bacteria, the immune system and obesity can lead to mental illnesses.

German scientists recently reported on their study, which demonstrated the influence of intestinal bacteria on losing weight and gaining weight. In any case, it has long been known that the intestinal flora affects physical health. There are also indications that these bacteria also have an impact on the psyche. A research group from Austria has now been able to gain new insights into how gut bacteria cause depression.

Changes in the brain

It has long been known that there is a real medical background for the proverbial “gut feeling”. As explained in a contribution by "scilog", the magazine of the Austrian Science Fund FWF (Fund for the Promotion of Scientific Research), the intestine has its own nervous system, which due to its size and complexity is also called "abdominal brain", and closely with it Brain is networked.

According to the experts, processes in the intestine cause changes in the brain and vice versa, psychological factors affect the intestine. However, it has not yet been fully clarified how far this interaction goes and how exactly it works. For example, there are indications that the intestine could be involved in the development of psychiatric diseases.

A research group led by Peter Holzer, Professor of Experimental Neurogastroenterology at the Medical University of Graz, is researching the complex interplay between the gut and brain. In a project funded by the Science Fund FWF, the team was able to identify some specific factors that can trigger psychological changes in mice.

Strong connection between brain and intestine

"The relationship between the intestinal nervous system and the brain has been known for a long time, but the situation has become more complex when you look at the most recently published work," says project manager Peter Holzer.

“In addition to the direct nerve conduction between the intestine and the brain, which has been known for a long time, there are many intestinal hormones that carry messages into the brain, as well as a huge immune system that releases messenger substances when stimulated. In recent years, the gut microbiome has also been added as a factor. This is a huge number of unicellular organisms that also release substances and probably play an important role in the information system. "

According to Holzer, many people know that there is a strong connection between the brain and the gut. “But we are generally not aware that so much information comes from the gut to the brain. This information is fed into brain areas that are important for our mood and emotions. ”

Illness is triggered

The Graz researchers examined different signaling pathways over which the processes in the intestine can influence the brain. According to the information, part of the project should clarify how certain bacteria in the intestine alarm the immune system and thus trigger a feeling of illness.

“The immune system learns early on to tolerate the microorganisms in the intestine. It starts with infancy, ”explains Holzer. "However, if some bacteria-generated substances penetrate the intestinal wall, this creates an immune response and goes hand in hand with the feeling that we are sick."

Specifically, the research group examined the so-called "endotoxin lipopolysaccharide" (LPS), which is released by certain intestinal bacteria and stimulates the immune system, so that we have the feeling that we are sick.

“Anyone who suffers from an infection with bacteria feels tired, has muscle pain, loses their appetite and withdraws. This is a sensible response from the body to deal with the infection quickly, ”said the scientist. "However, there is evidence that this reaction could be triggered by intestinal bacteria in humans if there is no infection at all."

The team was able to show that other substances produced by bacteria, so-called “peptidoglycans”, increase the effects of LPS. "Based on these findings, we believe that lipopolysaccharide is only one of several factors in the development of mental illnesses."

Being overweight increases your risk of depression

The neurogastroenterologist sees this physical reaction of "feeling sick" in the larger context of intestinal influences on psychological factors, in particular as a possible trigger for psychiatric illnesses.

"It is known from psychiatry and nutritional science that being overweight increases the risk of depression and depressive moods. And it has also been known for around 15 years that the gut microbiome is very different from healthy and very overweight people, ”said Holzer. One result of the project now gives concrete information about how processes in the intestine can trigger depressive behavior.

To arrive at the new findings, the scientists exposed mice to a high-fat diet and then analyzed their behavior. According to the information, it was not only the chemical change that was suitable for depression that was found in the brain, but also behavioral changes that were associated with depression.

According to Holzer, this is not easy to determine in mice, but it is possible. “Depressed people lose the joy of certain things. We were able to demonstrate this anhedonian, therefore listless behavior in the mice fed with high fat. ”For this purpose, the animals were offered normal water and, alternatively, sugar water. Healthy mice prefer sugar water, but the mice in Holzer's experimental set-up did so to a much lesser extent.

In order to find out whether intestinal microbes contribute to depressive behavior after a high-fat diet, the next step was to severely limit the intestinal microbiome using antibiotics. These results will be published shortly.

Possible signal path identified

The Graz team has also identified a possible signal pathway for how a high-fat diet leads to depressive behavior. The hormone "leptin", which is released by fat cells, seems to play a role in this. Mice that are unable to produce this hormone gain weight to the same extent as other mice when given high-fat food, but are not prone to the behavior associated with depression.

“The role of leptin has not yet been clearly clarified in the literature. In any case, we were able to show that leptin is important here, ”says Holzer, who suspects that the release of leptin is linked to short-chain fatty acids, which are produced by microorganisms in the intestine from fiber-rich food. As a result, the gut microbiome appears to play an important role in depression related to obesity. (ad)

Author and source information

This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.


  • scilog: How gut bacteria make you depressed, (access: August 25, 2019), scilog

Video: Anxiety and gut bacteria (July 2022).


  1. Galantyne

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  2. Arakora

    I congratulate, what words ..., remarkable thought

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