The Unlikely Relation Between Gut and Brain

By Allan Mai ‘20

Figure 1. The recent discovery of a gut-brain relation has generated enormous research interest in the topic.

With the high selectivity of the blood-brain barrier, it appears unlikely that microorganisms in the stomach could ever be able to reach the brain. However, past studies that have suggested major correlation between depression and specific gut bacteria and even correlation between social behavior and the activities of certain gut bacteria have sparked intense research regarding the “gut-brain” axis. Among these studies is the Belgium Flemish Gut Flora Project, which was conducted under the direction of principal author Mireia Valles-Colomer at the Rega Institute for Medical Research of the Katholieke Universiteit Leuven.

Researchers working on the Belgium’s Flemish Gut Flora Project used DNA sequencing to analyze the microbiota of the feces of over 1,000 human participants. Next, researchers correlated different microbial taxa with each participant’s quality of life based on self-reported and physician-supplied diagnoses. Their results demonstrated that levels of the bacteria Coprococcus and Dialister were reduced in those with depression while the butyrate-producing Faecalibacterium was consistently associated with higher quality of life indicators. The study also pointed to a positive correlation between quality of life and the potential ability of the gut bacteria to synthesize a breakdown product of dopamine. This breakdown product, known as 3,4-dihydroxyphenylacetic acid, serves as a one of the strongest pieces of evidence of the gut-brain relation.

Despite the implications of this study, the researchers stressed that these preliminary studies are only correlations; their present research methods are unable to demonstrate that microbiota in the gut directly trigger certain activity within the brain. Given that most current studies on the gut-brain relation utilize animal models, which are not very representative of the human “gut-brain” relation, there still remains extensive research to be done on the topic.



  1. M. Valles-Colomer, et. al., The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, (2019). doi: 10.1038/s41564-018-0337-x.  
  2. Image retrieved from:

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