The Gut-Brain Connection: How Your Digestive Health Affects Your Mood.
Written by Jessica Diakoumakos, Naturopath (BHSc Naturopathy) · Emba Wellness, Melbourne · Updated 14.04.2026
The gut-brain connection, or gut-brain axis, is the bidirectional communication network between your gastrointestinal tract and your central nervous system. It operates via the vagus nerve, the enteric nervous system, the immune system, and the circulatory system — meaning your gut and brain are in constant, real-time dialogue. The gut microbiome plays a central role in this system, producing neurotransmitters including serotonin, dopamine, and GABA, and generating metabolites that cross the blood-brain barrier and influence mood, cognition, and stress responses.
If you've ever had a gut feeling, felt sick with nerves, or noticed your digestion falls apart during a stressful week — you've already experienced the gut-brain axis in action.
This isn't metaphor. The connection between your gut and your brain is one of the most well-researched areas in modern neuroscience, and in clinical practice it's something I come back to constantly — particularly with clients managing mood, energy, or anxiety issues who are finding that conventional approaches are only getting them so far.
So let's get into the science. Here's what the gut-brain axis actually is, how it works, and why your gut health might be playing a bigger role in how you feel than you've ever been told.
What Is the Gut-Brain Axis?
The gut-brain axis is the bidirectional communication network connecting your gastrointestinal tract to your central nervous system. That word bidirectional matters — this isn't a one-way street where your brain tells your gut what to do. Your gut is constantly sending signals back up to your brain, influencing your mood, cognition, stress response, and more.
This communication happens through several pathways simultaneously: the vagus nerve, the enteric nervous system, the immune system, and the circulatory system. Research published in Cellular & Molecular Immunology in 2025 (Park et al.) describes this as a complex signalling network where microbiota-driven changes in gut and brain barriers, immune signalling, and neuronal pathways all interact to shape both physical and mental health outcomes.
Your gut is not just digesting food. It is actively participating in how you think and feel.
The Vagus Nerve — Your Gut-Brain Highway
The vagus nerve is the primary physical connection between your gut and your brain. It runs from your brainstem all the way down through your chest and abdomen, and research confirms that roughly 80% of vagal fibres are afferent — meaning they carry signals from the gut to the brain, not the other way around.
When your gut detects something — a bacterial metabolite, a change in gut lining integrity, a shift in the microbiome — it sends that information up the vagus nerve to your brainstem, where it's processed and projected to higher brain regions including the hippocampus and cortex. These are the regions involved in mood regulation, memory, and stress response.
A 2025 paper by Hwang and Oh in the International Journal of Molecular Sciences specifically examined how serotonin produced in the gut activates vagal afferent fibres, which transmit signals to the nucleus tractus solitarius in the brainstem — and from there outward to areas governing mood and cognition.
The vagus nerve is also a key part of your parasympathetic nervous system — the "rest and digest" mode. When vagal tone is healthy, it supports gut barrier integrity and helps regulate inflammatory signals. When it's impaired — through chronic stress, poor gut health, or dysbiosis — your body's ability to regulate inflammation and stress responsesbecomes compromised.
The Enteric Nervous System — Your Second Brain
Your gut has its own independent nervous system embedded in the walls of your gastrointestinal tract. It's called the enteric nervous system (ENS), and it contains around 500 million neurons — more than your spinal cord.
The ENS can function entirely independently of your central nervous system. It manages gut motility, secretion, blood flow, and local immune responses without needing to check in with your brain first. This is why gut function continues even after damage to the spinal cord, and why the gut is increasingly described as a "second brain" in the scientific literature.
But the ENS doesn't operate in isolation — it's in constant dialogue with your central nervous system via the vagus nerve and other pathways. Disruption to ENS function is increasingly being investigated in conditions like IBS, where this communication becomes dysregulated, contributing to hypersensitivity, altered motility, and pain perception.
Your Microbiome and Neurotransmitter Production
This is the part that surprises clients most when I explain it.
Your gut microbiome — the community of bacteria, fungi, and other microorganisms living in your digestive tract — is directly involved in producing the neurotransmitters that regulate your mood. Research confirms that gut microbiota are capable of producing or stimulating the production of serotonin, dopamine, and GABA (Loh et al., 2024).
Approximately 90% of your body's serotonin is produced in the gut, via enterochromaffin cells that line the intestinal wall. The gut microbiome influences this production by releasing short-chain fatty acids, which modulate the expression of tryptophan hydroxylase — the enzyme responsible for serotonin synthesis. That gut-derived serotonin then activates vagal afferent fibres, sending mood-relevant signals directly to the brain (Hwang & Oh, 2025).
GABA — your primary calming neurotransmitter — is also produced by gut bacteria. Certain species of Lactobacillusand Bifidobacterium have been shown to produce GABA directly, and research suggests this may influence anxiety and stress responses via the gut-brain axis.
What this means clinically is that if your microbiome is depleted or imbalanced — through antibiotics, a low-fibre diet, chronic stress, or infection — your capacity to produce these neurotransmitters can be compromised. This is one of the reasons I often look at gut health first when clients present with mood concerns that haven't fully responded to other interventions.
Short-Chain Fatty Acids and Brain Health
When the bacteria in your gut ferment dietary fibre, they produce short-chain fatty acids (SCFAs) — primarily butyrate, propionate, and acetate. These aren't just important for gut health. They cross the blood-brain barrier and directly influence brain function.
Research by Ramadan et al. (2025) shows that SCFAs interact with receptors in the brain — specifically GPR41 and GPR43 — where they modulate neuroinflammation and influence neurotransmitter release. Butyrate in particular has been shown to support the integrity of the blood-brain barrier, reduce neuroinflammation, and influence cognitive function and mood.
This is one of the most compelling arguments for a high-fibre, diverse diet — not just for your gut, but for your brain. Without adequate prebiotic fibre to feed the right bacteria, SCFA production drops, and so does the downstream support for brain health.
What This Means for You
The gut-brain axis is one of the most active areas of research in neuroscience right now — and understanding it changes how we think about mood, energy, and mental health.
If your gut health is compromised — whether through dysbiosis, poor microbial diversity, or conditions like SIBO or IBS— it doesn't just affect your digestion. It affects your neurotransmitter production, your inflammatory signalling, and your brain's ability to regulate stress and mood.
In the next post in this series, I go deeper into the clinical side: how gut dysbiosis specifically drives anxiety and depression, what the stress response has to do with your microbiome, and what a naturopathic approach to gut-brain health actually looks like in practice.
Read Part 2: Can Poor Gut Health Cause Anxiety and Depression?
If you've been told your IBS is just something you have to manage, you might want to read this.
Frequently Asked Questions
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The gut-brain axis is the two-way communication system between your gut and your brain. Your gut sends signals to your brain via the vagus nerve, the immune system, and chemical messengers including neurotransmitters and short-chain fatty acids. At the same time, your brain sends signals back down to the gut. The state of your gut microbiomesignificantly influences how effectively this communication system works.
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Yes — research confirms a direct relationship between gut microbiome health and mood regulation. The gut produces around 90% of the body's serotonin and is involved in the production of dopamine and GABA. A disrupted microbiome can compromise neurotransmitter production and increase neuroinflammation, both of which affect mood, energy, and mental clarity.
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The enteric nervous system is the network of around 500 million neurons embedded in the walls of your gastrointestinal tract. It can function independently of your brain and central nervous system, managing gut motility, digestion, blood flow, and immune responses. It is increasingly referred to as your "second brain" in the scientific literature.
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Short-chain fatty acids (SCFAs) are produced when gut bacteria ferment dietary fibre. They cross the blood-brain barrier and interact with receptors that modulate neuroinflammation and neurotransmitter release. Butyrate, one of the most well-studied SCFAs, supports blood-brain barrier integrity and has been linked to reduced neuroinflammation. Low SCFA production — typically caused by low dietary fibre and poor microbiome diversity — has downstream effects on brain function and mood.
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The vagus nerve is the primary physical highway between the gut and the brain. It runs from the brainstem to the abdomen, and approximately 80% of its fibres carry signals from the gut upward to the brain. When your gut microbiome produces metabolites or detects changes in the gut environment, it communicates these signals via the vagus nerve to brain regions involved in mood, cognition, and stress response.
Curious About Your Own Gut-Brain Health?
As a Microbiome Analyst and Healthy Gut Practitioner trained by Dr Jason Hawrelak at the Microbiome Restoration Center, I work with clients across Australia to assess and support gut health through functional testing, microbiome analysis, and targeted naturopathic treatment.
If you're dealing with mood, energy, or cognitive symptoms alongside gut concerns — or if you've simply never had your gut health properly investigated — this is worth exploring.
References
Hwang, Y. K., & Oh, J. S. (2025). Interaction of the vagus nerve and serotonin in the gut–brain axis. International Journal of Molecular Sciences, 26(3), Article 1160. https://doi.org/10.3390/ijms26031160
Loh, J. S., Mak, W. Q., Tan, L. K. S., Ng, C. X., Chan, H. H., Yeow, S. H., Foo, J. B., Ong, Y. S., How, C. W., & Khaw, K. Y. (2024). Microbiota–gut–brain axis and its therapeutic applications in neurodegenerative diseases. Signal Transduction and Targeted Therapy, 9(1), Article 37. https://doi.org/10.1038/s41392-024-01743-1
Park, J. C., Chang, L., Kwon, H.-K., & Im, S.-H. (2025). Beyond the gut: Decoding the gut–immune–brain axis in health and disease. Cellular & Molecular Immunology, 22(11), 1287–1312. https://doi.org/10.1038/s41423-025-01333-3
Ramadan, Y. N., Alqifari, S. F., Alshehri, K., Alhowiti, A., Mirghani, H., Alrasheed, T., Aljohani, F., Alghamdi, A., & Hetta, H. F. (2025). Microbiome gut-brain-axis: Impact on brain development and mental health. Molecular Neurobiology. Advance online publication. https://doi.org/10.1007/s12035-025-04846-0
