ZOE Science & Nutrition Most replayed moment: Fix Your Gut: Improve Your Mind | Dr Will Bulsiewicz
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Apr 28, 2026 
Dr Will Bulsiewicz, gastroenterologist and gut-health expert, explains the brain–gut axis and why gut and mood are so linked. He discusses how gut signals reach the brain, the enteric nervous system’s role, microbiome chemicals that affect nerve sensitivity and inflammation, and practical dietary approaches balancing low FODMAP relief with fibre and plant diversity.
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Gut Symptoms Often Come Before Mood Disorders
- There is a strong overlap between digestive disorders and mood disorders, with up to 50% of people with IBS meeting criteria for major depression or anxiety.
- Longitudinal studies show gut symptoms often precede mood problems, suggesting gut-first pathways in many cases.
Multiple Pathways Link Gut To Brain
- The gut and brain communicate continuously via bioactive chemicals, immune signals, hormones, neurotransmitters, and nerves like the vagus.
- Gut microbes produce many of these bioactive compounds and influence systemic inflammation and signalling to the brain.
Gut Neurotransmitters Influence Brain Via Precursors
- The gut produces most of the body's serotonin and a large share of dopamine, but gut-produced serotonin doesn't cross into the brain directly.
- A precursor, 5-hydroxytryptophan (5-HTP), can cross into the brain and alter neural signalling.
