Gut Microbiome May Hold Clues to Psychiatric Disorders

Investigators conducted a meta-analysis to assess perturbations in gut microbiota among patients with psychiatric disorders.

Depleted anti-inflammatory bacteria and elevated pro-inflammatory bacteria in the gut may be associated with certain psychiatric disorders, according to the results of a recent meta-analysis published in JAMA Psychiatry. These bacteria may therefore serve as biomarker targets for improved diagnosis, treatment, and monitoring of psychiatric disorders.

Researchers searched the Cochrane Library, PubMed, Embase, and PsycINFO for relevant studies published since 2005. Their search identified 16 reviews and 59 case-controlled studies that met their criteria. They evaluated microbiota among participants with major depressive disorder, bipolar disorder, psychosis and schizophrenia, anxiety disorders, obsessive compulsive disorder (OCD), eating disorders (anorexia nervosa and bulimia nervosa), autism spectrum disorder, attention-deficit/hyperactivity disorder (ADHD), and post-traumatic stress disorder (PTSD).

Of the studies reviewed, almost all (96.6%) identified significant differences between patients and controls at the genus, family, or phylum levels of the microbiota. For participants with major depressive disorder, 94 taxa were differentially abundant. In patients with psychosis and schizophrenia, the number climbed to 136; in those with bipolar disorder, 60; in those with anxiety, 36; in those with anorexia nervosa, 32; in those with OCD, 15; and in those with ADHD and PTSD, 9 and 3, respectively.

The researchers also found that findings among patients with major depressive disorder overlapped with those with bipolar disorder, psychosis, schizophrenia, and anxiety. In the microbiota, they observed notable changes in Faecalibacterium, Coprococcus, and Eggerthella. They found high levels of Lactobacillaceae, Clostridium, Klebsiella, and Megasphaera in participants taking psychiatric medication.

Overall, patients with psychosis and schizophrenia were found to have the highest microbe differences compared with control participants, while patients with anorexia nervosa were found to have the least.

Due to differences in microbiota, the researchers did not analyze children and older adults, which represents a potential limitation of the study. The study also did not allow for regional variations, such as differences between Eastern and Western cultures. Further, most studies had modest sample sizes.

The review “suggests a transdiagnostic commonality of microbial disturbances in [major depressive disorder], bipolar disorder, anxiety, and psychosis and schizophrenia, characterized by depleted anti-inflammatory butyrate-producing bacteria and enriched pro-inflammatory bacteria,” the researchers conclude. “The effect of key confounders such as psychiatric medication and diet should be carefully considered.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Nikolova VL, Smith MRB, Hall LJ, Cleare AJ, Stone JM, Young AH. Perturbations in gut microbiota composition in psychiatric disorders: a review and meta-analysisJAMA Psychiatry. Published online September 15, 2021. doi:10.1001/jamapsychiatry.2021.2573