As a psychologist who is doing her PhD in the field of nutritional psychology, I spend a whole heap of time thinking about how and why what we eat shapes our mental health. And, one of the key mechanisms that influences how what we eat impacts our mental health, is the gut microbiome (and to be honest, this is my favourite one to talk about!).
If you’ve ever experienced ‘butterflies in your tummy’ or a ‘gut feeling’, you’ll know that the connection between the gut and the brain is real! There is a complex, bidirectional network that connects our central nervous system and our gastrointestinal tract through the communication of neural, hormonal and immune pathways called the gut-brain axis (GBA). Now, you’ve probably heard of the vagus nerve, which is like the main motorway running through the GBA - this allows signals from the gut to travel up to the brain, and also brain signals to travel backdown to the gut.
Our gut microbiome is incredible – there are tens of trillions of microorganisms that live in our GI tract. In fact, the number of microbes present in the GI tract is estimated to be roughly equal to the number of human cells in our entire body!
The field of nutritional psychology is growing fast, with many studies looking into the role of the gut microbiome in mental health. I guess you could think of your microbiome as being like a rainforest – the more species diversity it contains, the more functional and resilient the whole system becomes… diversity really equals health. Dysbiosis, a word that refers to an imbalance of gut bacteria, can refer to too few beneficial microbes, too many unhelpful microbes, or less microbial diversity overall. The literature examining the role of dysbiosis in psychological disorders is well established, particularly with regards to depression, anxiety and schizophrenia. A 2025 systematic review revealed that certain mental health conditions have their own gut microbiome ‘fingerprints’ through very specific differences in gut dysbiosis in comparison to healthy controls. There was found to be…
Lower microbial diversity in depression
Fewer short chain fatty acid-producing bacteria in anxiety
Lower Lactobacillus in schizophrenia
And shifts in key microbial ratios in bipolar disorder.
Supporting this picture, a 2023 systematic review of eighteen studies concluded that dysbiosis played a “transcendental role” in several psychological disorders including depression, stress, and ASD.
It’s important to mention here that we are revealing a relationship (rather than a cause between gut bacteria and psychological disorders – the relationship is complex and bidirectional, and important for us to be aware of if we want to support our mind and body to thrive!
What we are learning is that a healthy microbiome equals a diverse microbiome (and, a diverse microbiome is important for your psychological health!). Back to my rainforest metaphor – if we just had one species of tree without any other species in there, it’s pretty vulnerable.
So, if diversity is the goal, how on earth do we cultivate it?! There are so many ways we can enhance diversity in our gut, but one way I’m keen to tell you about is through diet (and one part of our diet in particular!).
Let’s talk fermented foods! When we eat or drink fermented foods, they provide our guts with beneficial live microorganisms that influence the composition of our gut microbiome and support our metabolic health and immune system. A landmark 2021 study published in Cell by Wastyk and colleagues, found that a diet rich in fermented foods increased gut microbiome diversity and reduced immune activation markers. A more recent review even suggests that fermented foods can influence the gut-brain communication pathway we talked about earlier, as well as influencing immune function.
I want to be transparent here: the research specifically examining fermented foods and mental health outcomes is still in its early stages. So, whilst I can’t say ‘eat more kimchi to feel less anxious!'’, I can say that there is a strong and growing body of evidence showing that microbial diversity supports psychological wellbeing, that dysbiosis is meaningfully linked to depression and anxiety, and that fermented foods are one of the most effective dietary tools we have for building and sustaining that diversity. For me, that’s enough reason to include fermented foods in my diet every day. Personally, I am a huge fan of Clover Ferments to increase microbial diversity and promote the good bugs in my gut (and therefore benefit both my mind and body!). I use the tonics to make gut gummies or marshmallows that I keep in the fridge for easy snacks, and the spritzes on the go! If you are looking for an accessible, delicious way to enhance the diversity in your gut – there it is my friends.
Sophia Dawson
Guest written blog by Sophia Dawson,
Senior Psychologist
Check out Sophia's website here
https://www.wholeisticpsychology.com/
References
References
Annunziata, G., Arnone, A., Ciampaglia, R., Tenore, G. C., & Novellino, E. (2020).
Fermentation of foods and beverages as a tool for increasing availability of bioactive
compounds. Focus on short-chain fatty acids. Foods, 9(8), 999.
Balasubramanian, R., Schneider, E., Gunnigle, E., Cotter, P. D., & Cryan, J. F. (2024).
Fermented foods: Harnessing their potential to modulate the microbiota-gut-brain axis
for mental health. Neuroscience and Biobehavioral Reviews, 158, 105562.
https://doi.org/10.1016/j.
Barandouzi, Z. A., Starkweather, A. R., Henderson, W. A., Gyamfi, A., & Cong, X. S.
(2020). Altered composition of gut microbiota in depression: a systematic
review. Frontiers in psychiatry, 11, 536093.
Butler, M. I., Bastiaanssen, T. F., Long-Smith, C., Morkl, S., Berding, K., Ritz, N. L., ... &
Dinan, T. G. (2023). The gut microbiome in social anxiety disorder: evidence of altered
composition and function. Translational Psychiatry, 13(1), 95.
Clark, A., Mach, N., & Mach-Arum, N. (2025). Fermented foods as functional systems:
Microbial communities and metabolites influencing gut health and systemic outcomes.
Foods, 14(13), 2292. https://doi.org/10.3390/
Grau-Del Valle, C., Fernández, J., Solá, E., Montoya-Castilla, I., Morillas, C., & Bañuls,
C. (2023). Association between gut microbiota and psychiatric disorders: A systematic
review. Frontiers in Psychology, 14, 1215674.
https://doi.org/10.3389/fpsyg.
Liu, F., Li, J., Wu, F., Zheng, H., Peng, Q., & Zhou, H. (2019). Altered composition and
function of intestinal microbiota in autism spectrum disorders: a systematic
review. Translational psychiatry, 9(1), 43.
Mehta, I., Juneja, K., Nimmakayala, T., Bansal, L., Pulekar, S., Duggineni, D., ... &
Younas, S. (2025). Gut microbiota and mental health: a comprehensive review of gut-
brain interactions in mood disorders. Cureus, 17(3).
Prehn-Kristensen, A., Zimmermann, A., Tittmann, L., Lieb, W., Schreiber, S., Baving, L.,
& Fischer, A. (2018). Reduced microbiome alpha diversity in young patients with
ADHD. PloS one, 13(7), e0200728.
Shaikh, R. G., Dey, A., Singh, V. P., Khandagle, A., Naik, S., Hasan, A., & Singh Sr, V. P.
(2025). Understanding the impact of the gut microbiome on mental health: a systematic
review. Cureus, 17(1).
Wastyk, H. C., Fragiadakis, G. K., Perelman, D., Dahan, D., Merrill, B. D., Yu, F. B., ... &
Sonnenburg, J. L. (2021). Gut-microbiota-targeted diets modulate human immune
status. Cell, 184(16), 4137-4153.
Wilson, D. R., Binford, L., & Hickson, S. (2024). The gut microbiome and mental
health. Journal of Holistic Nursing, 42(1), 79-87.
