Gut microbiome, sometimes known as gut flora, refer to the microorganisms that live in our digestive tracts. Over the years, they have become one of the most popular topics in medical research. 

Every person has a different mix of bacteria in their system which may be associated with many types of diseases. For instance, having too much or too little of some kinds of bacteria might contribute to inflammatory bowel diseases. Studies have also examined if they could be linked to other diseases like multiple sclerosis and childhood leukemia.

While all of this covers physical health, how much of an influence does microbiome have over our mental health?

The answer has been unclear for the most since a majority of the studies on this link have only involved animals. But a recent study published in Nature Microbiology has been able to shed some light. 

Researchers from Belgium recruited more than 1,000 people in order to examine their gut microbiome. Of them, 173 participants were diagnosed with depression or fared poorly in a survey assessing their quality of life.

It was found that this subset of participants had lower than average levels of two kinds of microbes — Coprococcus and Dialister — compared to the other healthy participants. Furthermore, the levels were low regardless of whether the patients took antidepressants or not.

Exactly how these microorganisms influence the brain is yet to be understood. According to Science Mag, "one possible channel is the vagus nerve," which serves as a link between the gastrointestinal tract and the brain.

"This is the first time this kind of work has been done in such a large scale in humans. Most previous work has been done in animal models," Jeroen Raes, the lead author of the study, told Forbes.

Though the association is very strong, more research is needed to confirm that gut microbes alone can have an impact on mental health. The findings will also need to hold up in a more diverse group of participants as the new study focused strictly on Belgians.

And what happens next if future studies are able to establish causality? Raes, a microbiologist at the Catholic University of Leuven, told Mind Body Green that this could potentially pave the way for treatments in depression.

"One option is novel, next-generation probiotics. I really think there is a future in this: using cocktails of human-derived bacteria as treatment — bugs as drugs, as they say," he explained.

If there is one takeaway, it is a message for the public to avoid underestimating the impact on gut health. This would mean including more of plant-based foods in your diet and consuming enough fiber among other recommendations.