The gut-brain axis – communication between the gut microbiome and the brain
When was the last time something gave you a “stomach ache” or did you have a “good gut feeling” instead? Or is a new partner giving you “butterflies in your stomach” at the moment?
All these idioms show that the vernacular has long suspected what science was only able to prove later: the complex connection between our intestines and our brain!
Many people view the gut solely as a digestive organ and often overlook its fascinating complexity and numerous other functions. A particularly interesting field in this context is the gut-brain axis.
The gut-brain axis
Our intestines contain around 100 million nerve cells, which together form the so-called enteric nervous system. This functions almost independently of our brain, the central nervous system, and is only modulated by it.
One of the most important communication channels between the gut and brain is the vagus nerve. This extends from the brain over a considerable part of the body and is largely responsible for the two-way exchange of information between the gut and brain. Surprisingly, only 10% of all information traveling along the vagus nerve travels from the brain to the gut, while an impressive 90% is sent in the opposite direction – from the gut to the brain. This fact alone gives us an idea of the huge impact our gut has on our brain. Research has confirmed this and deepened our knowledge of the gut-brain axis.
The forgotten factor
For several decades, intensive research has been carried out into the communication between the gut and the brain. However, for many years an important, even decisive factor was forgotten: our gut microbiome. However, this omission has been corrected by science, particularly in the last decade, through intensive research into our gut-brain axis.
With trillions of our little roommates sitting in our gut, compared to only around 100 million nerve cells, it’s no surprise that they have a big say. Not only in matters relating to our diet, such as what we have an appetite for, but also in relation to our mood. The occurrence of diseases such as Parkinson’s, Alzheimer’s and autism also appears to be linked to the composition of our microbiome.
However, this raises a crucial question: Since an average bacterium is only a few micrometers in size, how can the signals it transmits overcome the comparatively enormous distance between the intestine and the brain?
Communication pathways: From the gut to the brain
Our gut microbes can communicate with our brain in three different ways:
- about our nervous system.
- about our immune system.
- via messenger substances in our blood.
Our gut bacteria are able to independently produce certain neurotransmitters, chemical messengers that transmit information between nerve cells. This allows them to interact directly with our nerves. Some of this information can be transmitted to the brain via the nerve pathways in our body, particularly the vagus nerve.
Indirectly, our gut bacteria can also influence how many of these chemical messengers the body releases. For example, it has been shown in model systems that the production of the happiness hormone serotonin is influenced by our microbiome. Germ-free mice, i.e. mice that had never come into contact with bacteria and were therefore completely sterile, showed a lower level of happiness hormones compared to their normally colonized counterparts.
What does that mean for us?
What direct, tangible effects does this communication between our gut microbes and our brain have on our health and well-being? How does the microbiota-gut-brain axis affect us?
Although it is obvious, as they can influence the production of the happiness hormone, it is nevertheless astonishing: our intestinal co-inhabitants have a say in our mood. For example, it was shown that mice that were given a substance that is normally produced by intestinal bacteria showed less depressive behavior.
In addition, a change in the gut microbiome has been observed in many neurodegenerative diseases, including Parkinson’s and Alzheimer’s. These results provide promising evidence that our microbiome plays an important role in these diseases. However, it remains to be clarified whether these changes are the cause or the consequence of the disease. Despite this caution, the available data opens up a lot of room for the assumption that our microbiome plays a decisive role in these disease processes.
What does the future hold?
The research field of the gut-brain axis is growing rapidly. New discoveries are being made almost daily and it seems extremely promising that our microbiome will increasingly be the target of therapies for various diseases in the coming years.
A healthy microbiome is therefore not just a “nice-to-have”, but can have a positive influence on our attitude to life and even our lifespan. A lot will certainly happen in this field in the coming years, new insights will be gained and the importance of our microbiome will continue to increase.
It therefore already makes sense to actively take care of the health of your own microbiome in order to optimally support the body as a whole. (LS)
Center image: Polushin Alexander – Adobe Stock
Further reading:
Morais LH, Schreiber HL 4th, Mazmanian SK. The gut microbiota-brain axis in behavior and brain disorders. Nat Rev Microbiol. 2021 Apr;19(4):241-255. doi: 10.1038/s41579-020-00460-0.
The essentials – microbes, the body’s hidden helpers. – Thomas C.G. Bosh
