By Dr Miguel Toribio-Mateas CBiol
It’s easy to think about mood as something that begins and ends in the brain. But that is only part of the story.
Your gut and your brain are in constant conversation. They communicate through nerves, hormones, immune activity, and the trillions of microbes that live in your digestive system. This is one reason stress can affect your gut, and why what you eat can influence not only your energy, but also how steady and emotionally well you feel over time. Research on the gut-brain axis has grown rapidly over the past decade, and while it is still developing, one thing is becoming increasingly clear: gut health is not just about digestion. It is also connected to how you feel.
That does not mean food is a quick fix for low mood, anxiety, or burnout. Trust me, it is not. But it does mean that everyday food choices can become part of a gentler, more supportive foundation for emotional wellbeing.
Why the gut matters for mood
Your gut is home to a vast ecosystem of bacteria, yeasts, and other microbes, often called the gut microbiome. These microbes help break down parts of food that your body cannot digest on its own. In doing so, they produce substances that can influence inflammation, stress responses, and the way the gut and brain communicate.
Some of these microbes are also involved in processes linked with mood, including those related to neurotransmitters like serotonin, dopamine, and GABA. Others help support the gut lining and influence how the immune system responds. That matters because ongoing low-grade inflammation and poor gut health are both linked with worse mental wellbeing in many people.
Did you know?
The microbiome can begin to shift quite quickly when you change your diet. Some studies suggest measurable changes can happen within a few days. That does not mean your mood will transform overnight, but it does remind us that the gut is responsive, and that small, consistent changes can matter.
So, what is realistic? This is the question I am asked most often. The honest answer is that it depends. You are unlikely to notice a dramatic emotional shift from one drink or one meal, because gut-brain health tends to respond better to rhythm and consistency than to intensity.
Some people notice digestive changes first, such as less bloating or more regular bowel habits. Others notice better energy with fewer peaks and valleys. Changes in mood or resilience, when they happen, are usually more subtle at first. You may feel a little less flat, a little more even, a little less reactive. In my experience, and broadly in line with the scientific evidence, these shifts tend to take weeks rather than days. It also tends to work best when fermented foods and drinks are part of a wider pattern that includes fibre-rich plant foods, regular meals, sleep, and stress support.
A couple of studies worth knowing about
One of the most interesting human trials in this area came from Stanford University. People who ate a diet high in fermented foods - including kombucha - for 10 weeks experienced an increase in gut microbiome diversity, as well as a reduction in multiple inflammatory proteins. That matters because inflammation is one of the ways gut health may influence how we feel, both physically and emotionally.
Kombucha may sound like a new wellness trend, but it is actually a traditional fermented tea drink with a long history, most often linked to China and later to parts
1 Wastyk, H. C. et al. (2021). Gut-microbiota-targeted diets modulate human immune status.Cell, 184 (16), 4137–4153.e14. https://doi.org/10.1016/j.cell.2021.06.019
of Eastern Europe, where fermented foods and drinks have long been part of everyday ways of eating. Human research on kombucha is still at an early stage, but a 2024 controlled clinical study found that, in people eating a typical Western-style diet, drinking kombucha for just 4 weeks was associated with modest beneficial changes in the gut microbiome and in some markers linked with health. That cannot be taken to mean that kombucha improves mood directly, but it does suggest that it may have a place within a broader gut-brain-supportive pattern of eating.
For me, the most interesting thing about kombucha is not really the old idea of it being a “probiotic drink”. It is the tea. Tea is naturally rich in plant compounds called catechins, a type of polyphenol. During fermentation, some of these compounds are changed by the microbes involved in making the kombucha, and once they reach the gut, they can be further broken down into smaller forms that may be easier for the body and the gut microbiome to work with. These substances appear to help nourish certain gut microbes, including groups such as Bifidobacterium, Lactobacillus and Akkermansia, while also helping to create a gut environment that supports balance rather than inflammation That matters because the gut and the brain are closely connected, and some of the “smarter” substances produced from tea polyphenols may be absorbed and act more widely in the body, including in ways that are relevant to inflammation and brain health. So, for me, rather than thinking of kombucha simply as “a probiotic drink”, I believe it’s more helpful to see it as a fermented tea that provides both live microbes and microbiome-supportive plant compounds.
2 Ecklu-Mensah, G. et al. (2024). Modulating the human gut microbiome and health markers through kombucha consumption: a controlled clinical study. Scientific reports, 14(1), 31647. https://doi.org/10.1038/s41598-024-80281-w
3 Pérez-Burillo, S. et al. (2021). Green Tea and Its Relation to Human Gut Microbiome. Molecules (Basel, Switzerland), 26(13), 3907. https://doi.org/10.3390/molecules26133907
4 Hong, M., et al. (2022). Mechanisms Underlying the Interaction Between Chronic Neurological Disorders and Microbial Metabolites via Tea Polyphenols Therapeutics. Frontiers in microbiology, 13, 823902. https://doi.org/10.3389/fmicb.2022.823902
Top facts from a gut-brain scientist
- Fermented foods and drinks are not new. They have been part of traditional food cultures around the world for centuries.
- They can add live microbes and other helpful by-products of fermentation to the diet.
- They may support microbial diversity and immune balance.
- The evidence for direct mood improvement is promising, but still mixed, so it is better to think in terms of support rather than cure.
- And my motto: You do not need to overhaul your whole diet. Start where you are.
If there is one thing I hope you take from all of this, it is that food does not have to be perfect to be supportive. The gut-brain connection is not about chasing dramatic results. It is about small, consistent choices that help create a steadier internal environment over time. In Part 2, I’ll look at what that can actually look like in everyday life.
