21 May 2025
Lina Sailer
One direction, from the brain to the gut, has already been well researched and has led to valid findings - such as the fact that chronic stress can severely affect the gut microcosm and lead to various diseases. The “opposite lane” is less well understood. However, there are many indications that a disturbed gut flora also has a strong impact on mental health.
The human digestive system can process much more than just food, and this is no wonder when you take a closer look at the composition of this “super organ”. With more than 100 million nerve cells, the “enteric nervous system” in the intestine is the largest outside the brain and has four to five times as many neurons as the spinal cord. Trillions of bacteria in this small bodily universe perform vital tasks that are essential for health - they regulate the immune system, produce vitamins and messenger substances and convert indigestible carbohydrates into short-chain fatty acids, which keep the pH value in the large intestine low and thus ward off pathogens.
This sensitive ecosystem in the body only functions smoothly if the composition of the different types of bacteria is right. Many factors play a role in this - from genetic predisposition to diet and lifestyle. In 2015, researchers at Ohio State University discovered that even the temperament of babies is linked to the number and diversity of gut bacteria. The greater the diversity of bacteria, the calmer and more peaceful the babies studied were.
This study from the USA, for which 77 infants were tested, is a strong indication that the communication channel of the gut-brain axis works strongly in both directions, i.e. that the “gut brain” can very well influence what goes on in the actual brain. The microorganisms in the gut can apparently produce substances that affect mood, stress perception and cognitive functions, although the exact mechanisms in this complex system have not yet been conclusively researched.
In any case, previous studies have shown that patients suffering from depression or anxiety disorders also have an above-average incidence of bowel and digestive problems. Patients with Crohn's disease, on the other hand, have been found to have psychological side effects such as chronic fatigue or psychological complaints. There are also indications that the gut microbiome may be involved in autism, ADHD and schizophrenia. In many respects, however, research here resembles a circumstantial process in which conclusive evidence exists, but which still lacks incontrovertible proof. Even though it has been proven, for example, that the microbiome of children born naturally differs from that of newborns born by caesarean section, this does not resolve the neuronal, hormonal and immunological signaling pathways on the gut-brain axis in a way that leaves no more questions unanswered.
In short, the fact that there are interactions between the gut and brain from birth to dementia, in other words from the cradle to the grave, has been solidly researched. But what is the cause and what is the consequence remains unclear in many respects.
When it comes to the composition of the microbiome, there are factors that cannot be influenced, such as the type of birth, gender and age, as well as genetic disposition. But there are also factors that can be influenced, such as diet, smoking, alcohol and weight, and everyone can do something good for themselves.
Researchers at the University of Jena used probiotics, which are contained in natural yoghurt or sauerkraut, for example, in a study with test subjects suffering from depression. In the probiotics group, the symptoms of depression were reduced compared to the placebo group - but not sustainably, as the test period may have been too short. The BDNF level also increased in this group. In simple terms, this is a growth hormone that protects the nervous system, among other things, and whose levels fall in cases of depression or chronic stress.
What can be learned from this is that a healthy diet rich in vitamins and fiber, abstaining from nicotine, drinking little alcohol and not being overweight on the scales are certainly not wrong if you want to do your “super organ” gut some good.
Research into the gut-brain axis promises to be one of the most interesting scientific projects, but despite some promising results, it is still in its infancy. Nevertheless, there is much to suggest that disturbances in the gut microbiome have an impact on the brain - from autism and ADHD to depression and dementia, there appear to be links. A number of studies give hope that new approaches in the prevention and possibly also in the treatment of mental illnesses could emerge if this highly complex communication channel between the gut and brain can be decoded in a sustainable way.
Sources:
Die Verbindung zwischen Mikrobiom und mentaler Gesundheit sowie der mögliche Einsatz von Probiotika, Burgerstein Foundation, Micronutrients for Health, 26. September 2024.
Empfindliches Ökosystem – unser Mikrobiom, Universitätsklinikum Jena. Toddler temperament could be influenced by different types of gut bacteria, Science Daily, Mai 2015.
Wie die Darmflora die Psyche beeinflusst, Studie von Universitätsmedizin Mannheim und European Molecular Biology Laboratory Heidelberg, Oktober 2022.
Gute Bakterien gegen Depressionen, Universität Basel, 9. Juni 2022.
