How is gut health related to mental health?

The idea that our gastrointestinal system is related to our thoughts and actions lies deep within us, which word like "gut feeling" or the term "butterflies in the stomach" emphasizes so nicely. Therefore, an understanding of how our gut health can affect our thoughts and behaviors - and vice versa - is also an important part of the future prevention and treatment of a wide range of diseases - both mental and somatic..

How are the brain and gut connected?

You have probably heard the term "brain-gut-axis", which describes the biochemical signaling that takes place between the gastrointestinal tract and the central nervous system. The relationship between brain and gut is quite complex and their mutual communication can include many of the body's systems. For example, the brain is thought to communicate with the gut through the vagus nerve, which is a nerve located in your neck just below the brain. As the nerve is one of the longest and most branched nerves in the body, it affects almost all internal organs and provides, among other things, for the rhythmic movements in the intestines. In addition to being connected via nerve pathways, the communication between the brain and the gut is thought to go via intestinal hormones, the immune system and microbial metabolites such as short-chain fatty acids. (1). In summary, there is a good indication of a "communication pathway" between the brain and the gut that uses neural, hormonal and immunological "routes". If there is curling on the thread, ie dysfunction of this axis, it can have pathophysiological consequences for the host - or in good Danish, your intestinal flora will thus be able to create a lot of trouble for your state of health both physically and mentally.

The relationship between brain and gut is quite complex and their mutual communication can include many of the body's systems.

What do the brain and gut communicate about?

Although the mechanisms behind the communication between brain and gut are still not completely clarified, there is no doubt that the signals sent back and forth are quite clear. It is certainly not just cozy talk that is communicated between the brain and the gut, but their mutual communication consists of i.a. in maintaining and coordinating your gastrointestinal function and the feedback the brain receives from the gut can have an effect on your mood, your behavior and your cognitive function. Simplified, it can mean that there can be a great connection between how the environment is in your gut and what thoughts and feelings you have (1). The idea that microorganisms can be beneficial to our health is certainly not new either. As early as 1910, the British Journal of Psychiatry wrote about the successful treatment of melancholy with lactic acid bacteria. Another early proponent was the Russian Ilya Metchnikoff, who won the Nobel Prize in Physiology and Medicine in 1908. He was a great proponent of fermented milk, which he believed could remedy, among other things. fatigue and melancholy (2).

So far, the brain-gut relationship has been best elucidated in animal studies, where it has been shown that stress in animals drastically changes the composition of their microbiome, which is a term for all the microorganisms including bacteria found on and in your body, and which interact with your body in a positive way. It has also been shown that the administration of live bacteria (probiotics) to mice in sterile environments can attenuate the mice's response to stress. (2). Another study has shown an antidepressant effect in mice by giving them prebiotics, which in short are food components that can not be digested by human or animal digestive enzymes, but which stimulate the growth of beneficial bacteria in the digestive system. (3). The examples just mentioned show primarily that if there are changes in the bacterial composition in the intestine, then you also see a change in behavior. If you have to find a link the opposite way - that is, where a change in the brain leads to a change in the intestinal bacteria, then there is a Chinese study where the intestinal flora of Chinese patients was examined after a stroke (blood clot in the brain). Here it was seen that the composition of bacteria differed significantly from the healthy control group, which indicates that the changes in the brain could also be read in the intestinal bacteria (4).

Psychobiotics as a term, are used to describe specific probiotics that, when ingested in appropriate amounts, can provide a mental health benefit by affecting the microbiota of the host organism.

Let the revolution begin!

Understanding the interplay between brain and gut opens up completely new non-invasive treatment options for various disorders. Influencing the intestinal bacterial composition with probiotics, prebiotics or specially designed diets is virtually side-effect-free. As research into the relief of stress and depression has emerged, a new term called "psychobiotics" has emerged. Psychobiotics as a term, are used to describe specific probiotics that, when ingested in appropriate amounts, can provide a mental health benefit by affecting the microbiota of the host organism. So knowledgeable that research is done into the use of probiotics for many purposes, the type that is used targeted at psychiatric diagnoses is called psychobiotics or "psychobiotics". An entire book has been written about it, namely "The psychobiotic revolution" (5), so if you want to dive deeper into the world of psychobiotics, it's definitely worth reading.

They are what you eat!

Although the future of using regular food and supplements (pro- and prebiotics) as valid and safe treatment, there are still many factors that can affect the outcome of treatment. The biggest challenge is that our bacteria are constantly changing depending on your lifestyle. Your bacteria grow and multiply according to what you feed them. Therefore, a large part of the basis for a beneficial or perhaps even harmful intestinal flora must be found in your diet. If you primarily eat a lot of processed foods that contain little fiber, a lot of fat and a lot of sugar (ie a typical western diet), then you will not be able to make a revolutionary difference to your health no matter how many good supplements you consume. In short, a stable foundation must be formed with a healthy diet with lots of fiber from whole grains, fruits and vegetables as well as good plant-based fats and quality protein sources together with a possible supplement of pre- or probiotics before you see the full effect.

Your bacteria grow and multiply according to what you feed them. Therefore, a large part of the basis for a beneficial or perhaps even harmful intestinal flora must be found in your diet.

Despite the challenges of being able to completely control the process and the result by using diet, pre- and probiotics as treatment, it will in future be very advantageous to consider the role of the brain and intestine in a given disorder. After all, "just a gut feeling" seems to be more comprehensive than the proverb immediately suggests.

References

1. Foster et al. (2017) Stress & the gut-brain axis: Regulation by the microbiome. Neurobiology of Stress 7; 124-136
2. Bastiaanssen et al. (2018) Making sense of… the microbiome in psychiatry. International Journal of Neuropsychopharmacology 22; 37-52.
3. Burokas et al. (2017) Targeting the microbiota-gut-brain axis: Prebiotics have anxiolytic and antidepressant-like effects and reverse the impact of chronic stress in mice. Biol Psychiatry 82; 472-487
4. Yin et al. (2015) Dysbiosis of gut microbiota with reduced tri-methylamine‐N‐oxide level in patients with large‐artery ath-erosclerotic stroke  or  transient  ischemic    J  Am  Heart  Assoc 4:e002699.
5. Anderson, Scott C., Cryan, John F. & Dinan, Ted (2017): The psychobiotic revolution: Mood, food, and the new science of the gut-brain connection. Washington: National Geographic.