For years, digestion and mental health were seen as separate systems.
But new research — much of it from UK and European scientists — is revealing a powerful connection between your gut and your mind.
It’s called the gut-brain axis, and it may help explain why improving gut health can ease stress, lift mood, or even reduce anxiety and depression.
Mood, stress, and low energy are among the most common health concerns — and treatment is often limited to medication or therapy.
But what if your gut microbiome — the trillions of bacteria living in your digestive tract — could also play a role?
New evidence shows that gut microbes:
Produce mood-regulating chemicals like serotonin
Support your immune system and reduce inflammation
Communicate with the brain via the vagus nerve
It’s not a miracle cure. But gut health may be one of the most accessible and overlooked tools to support how you feel.
The gut-brain axis is the two-way communication system between your gut and your brain. It works through three main pathways:
1. Nervous system
The vagus nerve connects your gut and brain, carrying signals in both directions. It helps regulate digestion, stress responses, and emotional state.
Your gut also has its own "second brain" — the enteric nervous system — made up of over 100 million nerve cells.
2. Chemical messengers (neurotransmitters)
Your gut microbes help produce neurotransmitters like:
Serotonin: Around 90–95% of the body’s serotonin is made in the gut. While this serotonin doesn’t cross into the brain, it still influences mood indirectly by acting on the vagus nerve, immune system, and inflammatory pathways — all of which affect how we feel.
GABA and dopamine: Certain microbes influence levels of these calming and reward-related chemicals.
3. Immune system
About 70–80% of the immune system is based in the gut.
Healthy gut microbes strengthen the gut lining and produce short-chain fatty acids like butyrate, which:
Reduce gut inflammation
Help regulate immune responses
Support mood through anti-inflammatory pathways
When the gut becomes overly permeable (“leaky gut”), it may allow bacterial fragments into the bloodstream, triggering low-grade inflammation linked to fatigue, low mood, and brain fog.
Butyrate is a short-chain fatty acid made when gut bacteria ferment fibre. It supports gut barrier function, reduces inflammation, and may affect the brain by:
Helping maintain the blood–brain barrier
It may stimulate brain-derived neurotrophic factor (BDNF) — a protein that helps neurons grow and repair.
It reduces neuroinflammation, which is linked to depression and brain fog.
More butyrate = calmer gut + calmer brain.
1. Shared microbial patterns in mental health
A 2022 systematic review in Molecular Psychiatry examined the gut microbiota composition in psychiatric disorders, including depression and anxiety.
It found consistent trends: individuals with these conditions had lower levels of anti-inflammatory bacteria such as Faecalibacterium prausnitzii, and higher levels of potentially pro-inflammatory species like Eggerthella.
2. Probiotics may support mood
A pilot trial from King’s College London (2023) reported that probiotic supplementation alongside antidepressants appeared to improve mood and sleep quality in people with major depressive disorder.
Note: This was a small study, and the peer-reviewed publication is pending.
3. Gut microbes linked to mood in population studies
The Flemish Gut Flora Project, involving over 1,000 participants, found that people with depression had consistently lower levels of Coprococcus and Dialister — two bacteria associated with higher quality of life and mental wellbeing.
These findings were replicated in a second group, strengthening the results.
4. How quickly can changes occur?
One 3-week study found that prebiotics reduced cortisol and improved emotional processing.
Another 4-week trial showed that daily prebiotic fibre reduced anxiety in healthy women.
5. Diet and fibre matter
A Stanford study found that increasing fermented food intake over 10 weeks significantly increased microbial diversity and reduced inflammation.
| Step | Why It Helps | Examples |
|---|---|---|
| Eat more prebiotic fibre | Feeds good bacteria, boosts butyrate | Inulin, oats, onions, leeks, bananas |
| Add fermented foods | Increases diversity and live cultures | Kefir, sauerkraut, miso, live yoghurt |
| Try a probiotic supplement | May support mood, anxiety, and sleep | Multi-strain acidophilus or bifidus |
| Cut ultra-processed foods | Reduces inflammation and gut imbalance | Cook from scratch, eat wholefoods |
| Manage gut inflammation | Supports barrier integrity and immune balance | Magnesium, zinc, turmeric, fibre |
The gut-brain axis is real — and growing evidence shows the microbiome may influence mood, stress, and mental wellbeing.
While not a replacement for therapy or medication, small steps like increasing fibre, fermented foods, or probiotics could offer a safe, evidence-based way to support how you feel.
1. Can gut bacteria really affect your mood?
Yes. They influence brain chemistry, inflammation, and communication via the vagus nerve. Studies show different gut patterns in people with and without depression.
2. What kind of probiotic helps with mood?
Multi-strain formulas containing Lactobacillus and Bifidobacterium species show the most promise in trials.
3. How quickly can gut support improve mood?
Some people notice benefits in 3 to 8 weeks, especially with fibre or probiotics. But results vary by person.
4. Does serotonin from the gut affect the brain?
Not directly. Gut-made serotonin doesn’t cross into the brain, but it influences mood indirectly by acting through the vagus nerve, immune system, and local inflammation.
5. Can turmeric help with gut inflammation?
Yes — turmeric (especially with black pepper) has anti-inflammatory properties and may support gut barrier health, though more human studies are needed for mood-specific benefits.
6. Is this advice suitable for everyone?
Most people can safely add more fibre and fermented foods — but if you have a medical condition or digestive disorder, speak with your GP or a dietitian first.
This article is for general information only and is not intended to treat or diagnose medical conditions. If in doubt please check with your GP first.
References:
McGuinness AJ et al. (2022). A systematic review of gut microbiota composition in people with psychiatric disorders. Molecular Psychiatry, Nature.
King’s College London. (2023). New data demonstrates potential role of probiotic supplementation in adults with major depressive disorder.
Valles-Colomer M et al. (2019). The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, 4, 623–632.
Schmidt K et al. (2015). Prebiotic intake reduces the waking cortisol response and alters emotional bias in healthy volunteers. Psychopharmacology.
Johnstone N et al. (2021). Galacto-oligosaccharides improve anxiety in healthy females: A randomised double-blind clinical trial. Scientific Reports, 11:9681.
Wastyk HC et al. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(13), 4137–4153.e14.
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