Current findings on the gut-brain relationship challenge long-held beliefs about psychological wellbeing because they turn the focus away from psychological dysfunction as the source of illness.

Dr. Mayer's theories, instead, turn science toward the idea of a symbiotic relationship between the mind and body. Moreover, according to Dr. Mayer, what and how we eat, the nature of our digestive processes and the neuroses we regularly cope with may have a lot to do with one another.

One has to wonder then: is the proper balance of microbes in the gut a prerequisite for optimal mental health?

Depression - which affects over 25 million people in the US - is commonly described as a chemical imbalance in the brain caused by a deficiency of serotonin. Today, thousands of people receive medication such as Prozac and Paxil to treat their depression. But what if antidepressants treat the symptoms rather than the cause?

It is a common misconception that serotonin is only stored in the brain.

According to Dr. Mayer, 95% of this substance is located in 'specialized cells' in the gut and is mostly influenced by what we eat. These cells are connected to nerve-cells that communicate with the brain's limbic system — which is responsible for regulating emotions.

A team of researchers led by Professor Jeroen Raes from the Catholic University of Leuven has analyzed the fecal microbiome data of over 1,054 individuals enrolled in the Flemish Gut Flora Project (FGFP). "We identified several groups of bacteria that seem to correlate with depression and quality of life in a diverse group of people," claims Raes. The researchers demonstrated that Coprococcus and Dialister are two bacteria that are associated with a higher quality of life.

Raes' team found that a low count (or absence) of the bacteria mentioned above, impacts mental health negatively. Coprococcus and Dialister are responsible for producing an anti-inflammatory compound known as butyrate, a fatty acid produced by the gut flora while breaking down certain varieties of fiber. This substance reinforces the intestine's epithelial barrier and reduces inflammation. 

As a consequence, some individuals who are a victim of mental health disorders could, in reality, be experiencing symptoms of gut inflammation. Although scientific research cannot confidently affirm that depression can be cured by modifying the gut's microbiome, Raes' research is the first step towards finding out whether there is a correlation between the two.

The FGFP's team will continue to conduct experiments in 2020. Raes states that their "goal would be to isolate these specific bacteria and culture them in animal models to see if they elicit or change behavioral traits. If this is proven, then the next step would be to set up human trials to see if procuring these bacteria can improve symptoms in people with depression."

Ultimately, the primary challenge science faces in proving gut microbiota could help heal adverse mental conditions is determining what exactly constitutes a healthy gut microbiota.

While the aforementioned microbiota Coprococcus and Dialister were shown to be increased in those with more a positive relationship to life, they are only two microbes of many. The gut biome, which is highly specific to each individual like a fingerprint, may indicate that higher prevalence of certain microbes proven beneficial for some are not beneficial for all.

The need for further research on the gut-brain relationship has never been more apparent.


Mayer, E. (2018). The Mind-Gut Connection: How the Hidden Conversation within our bodies impacts our mood, our choices, and our overall health. 

Valles-Colomer, M. et al. (2019). The neuroactive potential of the human gut microbiota in the quality of life and depression. Nature Microbiology.