How your gut microbiome shapes anxiety

By Dr. Liji Thomas, MDReviewed by Benedette Cuffari, M.Sc.Mar 12 2025

A recent study explores the intricate connection between gut bacteria and mental health, revealing how microbiome imbalances may contribute to anxiety disorders—and how probiotics might help.

Study: The Impact of Gut Microbiota on the Development of Anxiety Symptoms—A Narrative Review. Image Credit: Shutterstock AI Generator / Shutterstock.com

In a recent study published in Nutrients, researchers examine the role of the gut microbiome in the development of anxiety disorders.

How does the gut microbiome affect mental health?

Bacteria, viruses, bacteria, fungi, and archaea within the gastrointestinal microbiome interact with each other to support digestion and nutrient absorption, as well as immune function, metabolism, and neurotransmission.

In addition to genetics, environmental factors like age, diet, and geographical location can alter the composition of the gut microbiome. For example, the consumption of fiber-rich and fermented foods can support the proliferation of beneficial bacteria, whereas highly processed diets can lead to gut dysbiosis.

Dysbiosis refers to an imbalance of microorganisms in the gut microbiota, which can lead to a wide range of health problems. Several studies have reported that gut dysbiosis can induce dysfunction in the gut-brain axis, which increase the risk of mental health disorders like anxiety and depression.

Brain function can also be impacted by gut dysbiosis through its effects on the hypothalamic-pituitary-adrenal (HPA) axis, which subsequently alters the synthesis and secretion of neurotransmitters. The levels of dopamine, gamma-aminobutyric acid (GABA), and acetylcholine, all of which are neurotransmitters that have been implicated in mental health disorders, can be affected by gut dysbiosis.

The gut microbiome and anxiety

Previous studies have reported that the microbiome is less diverse and numerically abundant in patients with generalized anxiety disorder (GAD) as compared to controls. These abnormalities persisted even during remission in one study, thus suggesting the role of the gut dysbiosis the in GAD development.

The presence of certain bacteria species like Eubacterium and Coprococcus, while Blautia and Butyricicoccus may reduce the risk of anxiety. Likewise, probiotic supplementation with Lactobacillus and Bifidobacterium may protect against mental illnesses by promoting the growth of beneficial microorganisms.

Simultaneously, probiotics may also suppress the proliferation of pathogenic species such as Eschirichia-Shigella, Fusobacterium, and Ruminococcus gnavus. These pathogenic bacteria can increase gut permeability and systemic inflammation, both of which are implicated in anxiety symptoms.

Mechanisms underlying GAD-gut dysbiosis associations

Beneficial bacteria produce GABA and other metabolites that affect vagal nerve signaling from the gut to the brain. GABA is an inhibitory neurotransmitter that reduces the intensity of anxiety and stress responses. Therefore, low levels of these beneficial bacteria can amplify the intensity and frequency of these responses.  

Gut dysbiosis is associated with reduced epithelial integrity, which allows inflammatory molecules to enter the bloodstream. Chronic inflammation has been attributed to increased anxiety and altered brain functioning.

Short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate exert anti-inflammatory properties within the brain and participate in neurotransmitter activity. Faecalibacterium prausnitzii and Blautia are SCFA-producing bacteria in the gut microbiome. Thus, gut dysbiosis can interfere with SCFA metabolism to increase the risk of mental health disorders.

The effect of probiotics

Numerous probiotic formulations have been developed and investigated for their potential to alleviate symptoms of anxiety and depression with varying levels of success.

Supplementation with Lactobacillus plantarum P8, for example, was found to reduce stress and anxiety symptoms while also reducing inflammatory cytokine levels. Similarly, a probiotic intervention containing Bifidobacterium longum led to reduced perceived stress and improved sleep quality as compared to placebo recipients.  

Multi-component probiotic formulations have also been shown to reduce anxiety, depression, and stress levels. For example, one study found that patients who took both 25 mg of sertraline and a probiotic consisting of Bifidobacteirum bifidum, Bifidobacterium lactus, Bifidobacterium longum, and Lactobacillus acidophilus led to a significant reduction in anxiety levels than the placebo group.

The use of these substances and products can be applied both in the prevention and alleviation of existing emotional disorder symptoms by promoting appropriate dietary habits.”

Conclusions

Gut dysbiosis is often observed in patients diagnosed with various forms of anxiety disorders. The presence of gut dysbiosis is related to anxiety disorders, which indicates a possible therapeutic role for probiotics in treating these conditions.

Although probiotics may improve anxiety symptoms, additional studies are needed to validate these findings and determine the appropriate strains, dosage, and duration of therapy for this indication. Future research must also elucidate the pathophysiological pathways through which the gut microbiota affects the brain.