The majority believes that the gut is merely a digesting machine - something that digests food and transfers it. Science is telling us a far more important story. The gut is now being referred as the second brain, and it is a good reason. Huge numbers of millions of microorganisms, bacteria, viruses, fungi and other small living organisms live deep within your digestive system, in a collective known as the gut microbiome.
What scientists have discovered over the past several decades is that these microorganisms do much more than aid in digestion of food. They talk to your brain. And when that discussion backfires, the state of mind may be damaged.
The gut and the brain are interconnected by a two way communication highway known as the gut-brain axis. The system consists of the vaguus nerve, the immune system, hormones and chemical messengers known as neurotransmitters.
The most remarkable thing about this connection is that most of the serotonin, which is one of the primary chemicals that regulate the mood, is actually generated in the gut rather than in the brain (approximately 90 percent). This is in itself sufficient to inform us that something that is occurring in our intestines directly affects our emotional and mental well-being.
Studies have found that individuals with various mental health conditions such as depression, anxiety, and schizophrenia usually possess a significantly different gut microbiome make up than healthy counterparts.
In a landmark study, recently published in the journal, Nature Microbiology, in 2019, two sets of gut bacteria, namely, Coprococcus and Dialister were repeatedly low in individuals diagnosed with depression, even after adjusting the antidepressant use. This was among the best pieces of evidence indicating that certain bacteria are related to depression among human beings.
I believe it is incredible that even a small little bacteria that resides in your intestine can make you feel sad, anxious or even how well you think. But the science continues to point towards that. In case of the imbalance of the gut microbiome, so-called dysbiosis, the body falls into the state of low-grade inflammation.
This inflammation may enter the brain by a mechanism which destroys the blood-brain barrier causing neuroinflammation. The emergence of depression and anxiety disorders have been directly related to neuroinflammation.
Another activity of the gut microbiome is regulating the synthesis of short-chain fatty acids (SCFA), which are synthesized by the degradation of dietary fiber by gut bacteria. Butyrate (SCFAs) have a highly significant role in safeguarding the brain health. They decrease inflammation, encourage the health of the gut lining and even affect the expression of the genes that impact the brain activity.
Persons with such conditions as an autism spectrum disorder (ASD) and bipolar disorder have been identified to have low levels of SCFAs. A 2021 study in Cell has shown that gut bacteria directly control the synthesis of these acids and that the lack of these acids may cause abnormal brain development in animal models.
Studies in animal studies have also proved to be very educative. When germ-free mice that is mice raised in the absence of any gut bacteria whatsoever were observed, the researchers noted increased stress responses, anxiety-like behavior, and brain chemistry alterations.
After scientists had grafted the intestinal flora of anxious mice into the calm mice, the latter started to act like they were frightened. Such experiment is called fecal microbiota transplant (FMT) research, and is actively being investigated in humans as a possible treatment of some mental illnesses.
The other significant field to consider is the microbiome in the production of the principal calming neurotransmitter in the brain, gamma-aminobutyric acid (GABA). Some species of Lactobacillus and Bifidobacterium bacteria have been known to produce or induce GABA. There is a close relationship between anxiety disorders and depression with low GABA activity.
This informs us that probiotic treatment, which is the deliberate insertion of useful bacteria in the intestines, may emerge as a valid means of treating mental disorder in the future. More clinical trials are currently underway to test this concept, with some early findings suggesting it is an effective one.
Among the most influential means of influencing the gut microbiome is diet. The diet with high content of processed food, sugar, and artificial additives is more likely to minimize the diversity of microbes and cultivate dysbiosis. Conversely, a Mediterranean nutrition plan replete in fruits, vegetables, whole grains, legumes, and fermented foods have been identified to contribute to a healthier and more diverse microbiome.
In the SMILES trial, which was published in the journal of BMC Medicine in 2017, it was established that a dietary intervention could reduce symptoms of depression significantly in subjects receiving it as compared to social support as an intervention alone. This marked the beginning of demonstrating the fact that food is not merely fuel, it is medicine to the mind.
I think we have not yet read the first chapters of finding out the extent to which this gut-brain connection goes. However, the already existing evidence is sufficient to consider. It is not brain chemistry or life experiences that only matter when it comes to mental health, but rather, mental health is much related to the ecosystem living in your gut.
Maintaining that ecosystem via diet, stress reduction, proper sleep, and perhaps specific probiotics can be among the most underestimated actions an individual can take to improve his/her mental health.
It can be expected that the future of mental health treatment will look quite different than it does today. In the future, psychiatrists can prescribe customized microbiome treatment options in conjunction or even substituting standard drugs. To conclude, the most critical lesson, as of today, is the following: gut health is more important than most people think it is, and taking care of it is taking care of your mind.