Evidence-Based Reviews

Gut microbiota and its implications for psychiatry: A review of 3 studies

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Study design

  • A cross-sectional study of 76 patients in Zhejiang, China. Forty patients with GAD in the active state and 36 healthy controls were compared in terms of composition of GI microbacterial flora.
  • Researchers also examined a subgroup of 12 patients who were treatment-naïve and 17 controls. Stool samples were collected from the 12 patients who were treatment-naïve before initiating medication.
  • Researchers also conducted a prospective study in a subgroup of 9 patients with GAD in both the active state and remissive state. Two stool samples were collected from each patient—one during the active state of GAD and one during the remissive state—for a total of 18 samples. Stool samples analyzed with the use of polymerase chain reaction and microbial analysis.
  • Patients completed the Hamilton Anxiety Rating (HAM-A) scale and were classified into groups. Those with HAM-A scores >14 were classified as being in the active state of GAD, and those with scores <7 were classified as being in the remissive state.


  • Among the samples collected, 8 bacterial taxa were found in different amounts in patients with GAD and healthy controls. Bacteroidetes, Ruminococcus gnavus, and Fusobacterium were increased in patients with GAD compared with controls, while Faecalibacterium, Eubacterium rectale, Sutterella, Lachnospira, and Butyricicoccus were increased in healthy controls.
  • Bacterial variety was notably lower in the 12 patients who were treatment-naïve compared with the control group.
  • There was no notable difference in microbial composition between patients in the active vs remissive state.


  • Patients with GAD had less short chain fatty acid–producing bacteria (Faecalibacterium, Eubacterium rectale, Sutterella, Lachnospira, and Butyricicoccus) compared with controls. Decreased formation of short chain fatty acids could lead to GI barrier disruption. Fusobacterium and Ruminococcus were increased in patients with GAD. Fusobacterium can cause disease and be invasive when it disseminates within the body. The inflammatory characteristics of Fusobacterium contribute to the immunologic activation in GAD. Ruminococcus breaks down mucin, which could then increase GI permeability by mucous degradation of the GI lumen.

Changes in food processing and manufacturing have led to changes in our diets. Changes in our normal GI microbacterial flora could lead to increased gut permeability, bacterial dissemination, and subsequent systemic inflammation. Research has shown that the composition of the microbiota changes across the life span.9 A balanced intake of nutrients is important for both our physical and mental health and safeguards the basis of gut microbiome regulation. A well-regulated gut microbiome ensures low levels of inflammation in the brain and body. Lifestyle modifications and dietary coaching could be practical interventions for patients with psychiatric conditions.5 Current advances in technology now offer precise analyses of thousands of metabolites, enabling metabolomics to offer the promise of discovering new drug targets and biomarkers that may help pave a way to precision medicine.


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