It is estimated that 7.3% of the global population experiences an anxiety disorder of some kind, translating to over 600 million people1. With the recent interest in gut health and our evolving understanding of how the gut microbiome influences normal bodily function, the gut-brain connection is also gaining attention within the scientific community. From this interest, a fundamental question is emerging: can gut health affect anxiety?
This article explores the gut-brain connection, how gut health may contribute to anxiety and mental health, and the evidence-based strategies, such as lifestyle interventions and probiotic strategies, that may support those experiencing anxiety.
The gut-brain axis, or gut-brain connection, describes the bidirectional communication between the gut and the central nervous system, including the brain and spinal cord.
This communication happens naturally through the vagus nerve, which runs from the brain to the intestine and acts as the main channel where information is transmitted from the abdomen through to the brain2.
Several types of molecules can activate the vagus nerve. The gut contains the largest concentration of the body’s primary defence system: immune cells. It is also the site where neurotransmitters, the body’s chemical messengers, are made. Together, these molecules can activate vagus nerve fibres, travel through the bloodstream, or deliver signals to the nervous system to send key messages to the brain3.
When individuals experience stress, the impact is not just external; it can be internal as well. Stress directly impacts the brain, which can relay signals to the gut that promote microbiome alterations. These changes can upset digestive function and may contribute to conditions such as irritable bowel syndrome (IBS)4.
Anxiety is one of the most common reactions to stress. A gut under stress and anxiety often does not function quite as it should, and a variety of symptoms can appear:
These are reactions to the brain’s stress response, which activates the nervous system and shifts the body’s focus away from digestion and towards survival. The release of stress hormones, such as cortisol and adrenaline, and the resulting inflammation, drive these effects4.
Many of these symptoms overlap with IBS and other gut disorders. For example, slow gut motility is linked to small intestinal bacterial overgrowth, and increased intestinal permeability is sometimes described as “leaky gut”5. In a study of more than 2,000 patients, severe anxiety was four times more prevalent in patients with gastrointestinal symptoms6, highlighting the key connection between gut health and anxiety.
The impact of stress on the gut goes beyond functional changes. There is also a key connection between anxiety and the gut microbiome.
A study examining the gut microbiome of 117 people with depression and anxiety found that these disorders are linked to changes in the abundance of some gut microorganisms7. This link can be traced back to the production of neurotransmitters and short-chain fatty acids (SCFAs)8. Both act as chemical messengers to the brain and are produced by the gut microbiome. Changes to the gut microbiome can therefore affect the signals communicated across the gut-brain axis. These signals do not just regulate digestion; they also regulate mood, emotional processing and brain function9.
Observational and animal studies consistently link low gut microbial diversity and dysbiosis, an imbalance in microbial abundance, to poorer psychological outcomes10,11,12. For example, adolescents with major depressive disorder have been found to have a lower Firmicutes to Bacteroidetes ratio, higher abundances of Intestinimonas and Barnesiella, and reduced levels of Dialister and Collinsella bacteria11. This highlights how dysbiosis is associated with mental health and anxiety-related symptoms.
Several lifestyle habits can create powerful feedback loops between stress and digestive health. For example, sleep disruption elevates cortisol and activates the stress response system. Research shows this can impair the gut lining’s self-repair and reduce beneficial gut bacteria, while dysbiosis can, in turn, worsen sleep quality14.
Similarly, diets high in ultra-processed foods may damage the gut microbiome by depleting Bifidobacterium and Lactobacillus populations, weakening the intestinal barrier and dysregulating the gut-brain axis in ways that may heighten anxiety and depression15,16. For those under stress, psychological issues can further drive cravings for these same foods, perpetuating the cycle17.
Medication choices also matter. Even a single course of antibiotics can reduce microbial diversity for years, depleting SCFA-producing bacteria that are important in the stress response and brain function18,19.
To counteract these gut-unfriendly habits, healthier lifestyle choices can be made. Physical activity and regular exercise have consistently been shown to lower resting cortisol levels, improve sleep quality20, and encourage a healthier gut microbiome balance, actions that may strengthen stress resilience21.
There is a complex and highly evolved link between gut health and anxiety. Probiotics are a strategy used to promote a healthy gut microbiome, and there is emerging interest in the use of probiotics for anxiety. Known as psychobiotics, these probiotics consist of specifically selected strains that are believed to positively influence mental health.
Several clinical studies show promising evidence for the use of psychobiotics in anxiety.
In an exploratory study of 40 patients with IBS and mild to moderate anxiety and/or depression, supplementation with Bifidobacterium longum strains 1714 and 35642 for eight weeks not only improved IBS symptoms but also reduced feelings of anxiety and improved sleep quality22. Similarly, in a randomised controlled trial of 125 healthy adults, intake of Bifidobacterium longum R0175 alongside Lactobacillus helveticus R0052 for four weeks promoted positive effects on anxiety, emotional regulation and mindfulness23.
Across two randomised controlled trials using Lacticaseibacillus paracasei PS23, also known as HK-PS23, in highly stressed nurses and office workers, supplementation significantly improved anxiety and cortisol levels in nurses receiving the probiotic for eight weeks24. It also significantly improved sleep quality and anxiety levels in office workers while contributing to reduced gastrointestinal discomfort25.
Lactobacillus rhamnosus has also shown potential as a probiotic for anxiety. In the treatment of 30 IBS patients, Lactobacillus rhamnosus IDCC 3201 reduced symptom severity while improving perceptions of quality of life compared with placebo26. Evidence from a randomised controlled trial also shows that Lactobacillus rhamnosus HN001 CNCM I-3690, administered to students under exam stress, can promote a higher abundance of the beneficial gut bacteria Faecalibacterium prausnitzii, a change associated with lower self-reported anxiety levels before exams27.
While this evidence is promising, research is still in the early stages, and there is no single best probiotic for anxiety. Most studies use healthy populations that do not have a history of anxiety, so the evidence for psychobiotics as an intervention for clinically diagnosed mood disorders is limited28,29. In most cases, psychobiotics should only be considered as complementary interventions to existing therapies in individuals with anxiety and gut complaints.
To promote microbial diversity, nutritional and gut health support strategies should emphasise fibre-rich and fermented foods. However, current evidence suggests caution in overstating their mental health impact. Meta-analysis data from randomised controlled trials indicate that fibre supplementation alone does not reliably improve anxiety symptoms30, and human evidence for fermented foods in mood disorders remains sparse31.
For more evidence-based approaches, randomised controlled studies including patients with anxiety show that regular physical activity is effective in reducing anxiety symptoms32. For many people, a holistic lifestyle intervention, rather than a single approach, is key to managing gut health and feelings of stress and anxiety.
Anxiety is prevalent across the global population, but its impact can go beyond an external problem. Gut health and anxiety are closely linked, with stress inducing changes within the body that can adversely affect the diversity, abundance and function of the gut microbiome. The impact is not just one way; these changes can influence emotional regulation via the gut-brain axis and promote feelings of anxiety from within.
While evidence is still emerging, research with psychobiotics shows that specially selected probiotic strains can affect feelings of anxiety and improve gut health.
In practice, psychobiotics may not be suitable for all patients, and individualised, multidisciplinary management is important. However, a balanced approach that recognises the gut-brain axis and treats psychobiotics as a promising but still limited adjunct may be appropriate.
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