Gut–Brain Axis
The gut–brain axis describes the bidirectional communication between the gastrointestinal tract and the central nervous system. This signalling occurs through neural pathways (including the vagus nerve), hormonal routes, and immune mediators. Understanding the gut–brain axis is central to the BRAIN Diet, as dietary choices directly shape the microbial and metabolic signals that influence brain function.
Overview
The gut and brain are connected by:
- Neural pathways: The vagus nerve transmits signals from the gut to the brain and vice versa. Vagal stimulation has demonstrated clinical benefits in depression, epilepsy, and inflammation; gut microbes such as Lactobacillus can alter brain GABA receptor expression through vagal pathways.
- Neurotransmitter precursors: Gut health influences the production of neurotransmitters and their precursors, including serotonin, GABA, and dopamine. While gut-derived neurotransmitters are unlikely to cross the blood–brain barrier, precursors such as tryptophan and tyrosine do, enabling local synthesis in the brain.
- Microbial metabolites: Short-chain fatty acids (SCFAs) produced from fibre fermentation support intestinal barrier integrity, regulate immune responses, and promote synthesis of key neurotransmitters.
- Inflammatory signalling: When the gut barrier weakens, bacterial fragments such as lipopolysaccharide (LPS) can enter circulation, sustaining chronic low-grade inflammation that has been linked to disrupted dopamine and serotonin pathways.
Dietary Inputs That Support the Gut–Brain Axis
- Fibre and prebiotics: Support SCFA production and microbial diversity
- Fermented foods: Provide live microbes and postbiotic compounds; improved SCFA pools; vagal signalling
- Polyphenols: Support gut barrier and microbial diversity
- Omega-3 fatty acids: Help regulate inflammatory tone