The Gut Microbiome and Mental Health

By Alicia Dowsett
February 28, 2025
Brain Function, Brain Health, Gut Health Blog, Mental Health

The gut microbiome is a community of trillions of microorganisms, living in a symbiotic relationship in the intestinal tract. It’s made up of viruses, bacteria, fungi, and protozoa, playing a crucial role in regulating many aspects of our health including digestion, hormone regulation, immunity, vitamin synthesis, and neurotransmitter production. This ecosystem of microbes outweighs the number of cells in the body, and when out of balance, can impact health and lead to disease.

In the last two decades, there has been a lot of research supporting a strong bidirectional connection between the digestive system and the brain – this is known as the gut-brain axis. Links are emerging, connecting the gut microbiome to many psychiatric disorders, including depression, schizophrenia, autism, and anxiety; mental health conditions that previously were thought of as only originating in the brain.

Understanding this bidirectional network system opens new ways of thinking and offers alternate approaches to mental health. ^{1, 2}

This article explores how the gut microbiome influences mental health, what current research indicates, and some current management strategies.

The Gut-Brain Axis: The Bidirectional Link

The gut-brain axis is a communication network, linking the enteric (gut) and central nervous systems. Vagus nerve (a large “wandering” nerve that originates at the base of the brain, and relays messages to and from the gut and the brain) plays a key role in transmitting these signals ². This pathway enables constant communication via hormonal, neural, or immunological pathways, and as a result, each influences the other ³(Zhao et al., 2018). One way the gut microbiome influences brain function is through the production of neurotransmitters in the colon, e.g. dopamine, gamma-aminobutyric acid (GABA), and serotonin, all have important roles in mood, and cognition ^{2, 4}

Another way the gut microbiome influences brain function – both directly and indirectly – is through the production of short-chain fatty acids (SCFA) i.e., butyrate, acetate, and propionate. These SCFA are by-products of beneficial bacteria when they metabolise dietary fibre. SCFA are generally anti-inflammatory and may reduce neuroinflammation and oxidative stress, improve blood-brain barrier integrity, and stimulate the production of brain-derived neurotrophic factor (BDNF). BDNF is a protein that modulates neurotransmitter function and supports the growth, survival, and plasticity of neurons, which is often low in people with anxiety and depression. ^{2, 3}

Mental Health Disorders: What research is demonstrating

Research demonstrates that people living with mental health challenges such as those posed by depression, anxiety, and autism are more likely to have digestive issues, and those with depression commonly have reduced levels of specific gut bacteria such as Lactobacillus and Bifidobacterium compared to a control population without depression.²

Imbalances in the gut microbiome are referred to as dysbiosis, a reduction in the diversity of beneficial bacteria and an increase in pathogens, which can contribute to increased gut permeability. This allows potentially harmful substances such as lipopolysaccharides to enter the When this happens systemic inflammation can be triggered (or exacerbated) which can aggravate symptoms of anxiety and depression.⁴Lactobacillus and Bifidobacterium are two groups of beneficial bacteria that produce SCFAs and neurotransmitters, and their absence may contribute to the severity of depressive symptoms. This suggests that including probiotics of Lactobacillus plantarum LP01, Bifidobacterium longum BL04, may be beneficial for depressive-type disorders. ¹

The Role of Diet and Lifestyle

What we eat and how we live influences the diversity and balance of our microbiome. Lifestyle balance and diets rich in dietary fibre, polyphenols, fermented foods support the diversity and health of the gut microbiome. On the other hand, processed foods, (such as trans fats, and seed oils), lack of sleep, a sedentary lifestyle, and stress can all contribute to a reduction in diversity of the microbiome and increased pathogenic bacteria. This is dysbiosis, which is associated with nervous system imbalances. ⁵

The Mediterranean diet is high in dietary fibre, polyphenols, omega-3 fats, and . Studies demonstrate that people who adhere to this type of diet have higher microbiome diversity, and lower rates of anxiety and depression. ^5,6 This suggests that eating a nutrient-rich diet based on whole foods, variety, and omega-3 fats can have a positive influence on mental health outcomes by altering the gut microbiome.

In summary, the relationship between the gut microbiome and mental health is full of intrigue. Recent research has expanded our understanding of how the gut microbiome, inflammation, neurotransmitters, and the vagus nerve interact and impact mental health. The connection between gut and brain, via the vagus nerve, highlights the importance of addressing gut health, and the gut microbiome in those with mental health conditions. This new way of seeing and understanding mental health offers a fresh approach to an often-stigmatised group of disorders.

Armed with this understanding, it becomes easier to understand how a nutritious diet, quality sleep, low stress, a healthy lifestyle, and strain-specific probiotics may be effective strategies alongside more traditional psychological approaches, such as cognitive behavioural therapy (CBT), to enhance mental health and well-being.

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References

Evrensel, A., & Ceylan, M. E. (2015, December 31). The gut-brain axis: The missing link in depression. Clinical Psychopharmacology and Neuroscience, 13(3), 239-44.
Appleton, J. (2018, August). The gut-brain axis: Influence of microbiota on mood and mental health. Integrative Medicine: A Clinician’s Journal, 17(4), 28-32.
Zhao, L., Xiong, Q., Stary, C. M., Mahgoub, O. K., Ye, Y., Gu, L., Xiong, X., & Zhu, S. (2018, December 11). Bidirectional gut-brain-microbiota axis as a potential link between inflammatory bowel disease and ischemic stroke. Journal of Neuroinflammation 15, 339.
Merlo, G., Bachtel, G., & Sugden, S. G. (2024, February 9). Gut microbiota, nutrition, and mental health. Frontiers in Nutrition, 11, 1337889.
Ventriglio, A., Sancassiani, F., Contu, M. P., Latorre, M., Di Salvatore, M., Fornaro, M., & Bhugra, D. (2020, July 30). Mediterranean diet and its benefits on health and mental health: A literature review. Clinical Practice and Epidemiology in Mental Health, 16(Suppl-1), 156-164.
Yin, W., Löf, M., Chen, R., Hultman, C. M., Fang, F., & Sandin, S. (2021, Nov 27). Mediterranean diet and depression: A population-based cohort study. International Journal of Behavioral Nutrition and Physical Activity, 18(1), 153.