Intestinal bacteria influence people’s mood in many ways. The tiny microbes in your intestines take care of your metabolism, your digestion and even affect your mood and mood.

Your gut is inhabited by billions of bacteria. They sit in the mucous membranes of your intestinal walls and need an acidic environment in order to be able to carry out their tasks there. Researchers also call this construct the microbiome. More and more scientists recognize the importance of intestinal bacteria and an intact intestinal flora. The intestinal flora is understood to mean the entirety of all bacteria and microorganisms contained in your intestine.

The gut-brain axis

There is now overwhelming evidence of how important the microbiome actually is in our intestines and how far-reaching its influence on human health as a whole: The microbes are not only digestive aids that process the food they eat, they also support the body’s defenses and are in closely related to one’s own mood and the production of neurotransmitters in the brain.

The composition of the microbiome differs from person to person. Not everyone has the same number of intestinal bacteria, which is due to a wide variety of factors. Exposure to pathogenic agents, origin, birth, nutrition, sleep, stress, hygiene, environmental conditions and much more is relevant here. Half of all intestinal bacteria in everyone is the same, but the rest is individual.

Good and bad bacteria

Basically, there are both “good” and “bad” intestinal bacteria. The bad intestinal bacteria are called E. coli or putrefactive bacteria and can cause diarrhea and intestinal discomfort.
The good bacteria, on the other hand, are called pro-cultures. B. Lactobacteria and Bifidobacteria. They ensure that the intestinal flora and digestion function as desired and are responsible for ensuring that humans can absorb valuable nutrients and vitamins from food.

Both types of intestinal bacteria should always be in an appropriate ratio to one another, whereby the proportion of the pro-cultures should clearly predominate. If this is not the case and E. coli bacteria have colonized large parts of the intestine, then, in addition to digestive complaints, other complaints can occur which at first glance are hardly associated with the intestine. These include poor concentration, loss of performance and fatigue. A balanced intestinal flora is important if you want to stay fit and productive.

Scientific evidence

A team from the Gujarat Medical Council in India has shown that bacterial build-up or the condition of your intestinal flora is related to your mood.

The chairman of the research group Dr. Ketan Yogeshbai Pandya (MD) says:

Whether it is good or bad for you is the intestinal bacteria. If you want yourself to be fine, avoid stress and gluten. And get rid of parasites. Worms in the intestines eat good bacteria.

To understand how this works, you first have to know how the gut and brain “communicate” with one another. The intestinal-brain-intestinal communication takes place via the intestinal-brain axis and in both directions.

Biochemical explanation

The main route is via nerve connections in the spinal cord, another route is via the vagus nerve, which runs from the brain stem to the digestive system and is involved in many regulatory processes in the intestinal tract.

Experiments with mice have shown that the vagus nerve also functions as a direct connection between the microorganisms in the intestine and the central nervous system (CNS). The term “microbiome-gut-brain axis” is currently being established here.

Enteric nervous system

The enteric nervous system (ENS), a network of nerve cells that runs through the intestinal wall, is also essential to microbiome communication.

In the ENS and elsewhere in the body, neurotransmitters synthesized by intestinal microorganisms are transmitted by e.g. B. perceived chemosensors and can so z. B. communicate with the vagus nerve and downstream structures such as the brain and pass on information.
Another possibility of communication between the intestine and the brain is through hormones, such as B. GABA, neuropeptides and dopamine, as well as products that are produced by intestinal bacteria and are therefore at least partially to be regarded as messenger substances.

These include short-chain fatty acids (SCFA) and tryptophan, for example. With the expansion of the gut-brain axis to include the microbiome, the microorganisms that communicate with the CNS are now also called the “psychobiome”.

Intestinal bacteria and neurotransmitters

Researchers at Cork University in Ireland agree that the microbes in the intestinal flora influence the brain and your mood through various mechanisms.

So they found that gut bacteria are important building blocks for neurotransmitters like serotonin, dopamine and GABA, all of which play an important role in mood.

If your intestinal flora is now out of balance, this can negatively affect the production or conversion into the important neurotransmitters.

In the case of the neurotransmitter GABA, this is especially important against the symptoms of stress and for a restful sleep. GABA is only properly synthesized by the bacteria in the intestine and ensures that you come down and sleep well in the evening.

It becomes particularly interesting when you look at the connection between serotonin and the intestine. The intestinal bacterium Bifidobacterium infantis is involved in tryptophan synthesis, the basic building block for the hormone serotonin.
Over 95% of this building block is produced in your intestines and not, as is often wrongly assumed, in your brain. Based on this knowledge, research has begun on how to positively influence the intestinal flora. Perhaps the best-known human study, conducted at the University of California at Los Angeles, suggests that proculture capsules may be helpful.

The study situation

25 test subjects, all healthy women, were subjected to a test. For four weeks, 12 of them ate a cup of yogurt twice a day while the rest did not. Yogurt contains pro-cultures, live strains of bacteria, specifically Bifidobacterium, Streptococcus, Lactococcus and Lactobacilli.

Before and after the study, brain scans were performed on the subjects to measure emotions such as happiness, sadness, and anger. The results were very surprising because they showed significant differences between the two groups, with the yogurt test group showing consistently more positive emotions.

Stress and gut health
There are mutual relationships between the gut and stress. On the one hand, our psyche influences our intestines. In times of stress, many people react with indigestion, cravings or even loss of appetite. The reason for this is that more adrenaline and the stress hormone cortisol are released in stressful situations. The consequences are, for example, increased breathing and heart rates.

For these functions the body needs an enormous amount of energy reserves, which in this case are withdrawn from the gastrointestinal tract. As a result, normal activities in the gastrointestinal area are only performed to a reduced extent.
This results in z. B. Nausea and abdominal pain or diarrhea. Why every intestine reacts differently to stressful situations has not been fully scientifically clarified, but it is part of research in psychosomatics.

Hormonal impact

Another consequence of the increased release of stress hormones could be a change in the composition of the intestinal bacteria. For example, norepinephrine could affect the gene expression of the bacteria or the communication between the different bacteria, which can change the activity of the bacteria.

On the other hand, the evidence is becoming increasingly clear, or there have already been indications in animal experiments that our intestinal bacteria can also influence our psyche in a certain way.


A changed composition of the gut microbiome can have various causes. You can shift the balance of the good and bad intestinal bacteria so that the good intestinal bacteria die, which in turn can lead to digestive problems (e.g. diarrhea).

The result: there is no longer complete and sufficient absorption of important nutrients such as vitamins, minerals, etc.

[1] Pandya MD (2020) Plos I Pathogens. Neurochemical influence of intestinal bacteria on human behavior. Vol. 14. Issue 21
[2] Criaan MD; Dynan (2017) Nature Reviews Neuroscience. Microbiota and brain behaviour. Vol. 12
[3] Dillisch MD.; Labus MD (2019) Gastroenterology. Probiotic Products and their influence on the human Brain. Vol. 223. Issue 5.
[4] Quang; Park (2016) Journal of Neurogastroenterology and Motility. Probiotics for Brain Functions in Humans. Vol. 23. Issue 3


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