Gut Serotonin Production
How a healthy microbiome supports serotonin — and how dysbiosis disrupts it
✓ Healthy Gut
⚠ Gut Dysbiosis
✅
Optimal serotonin levels supporting mood, digestion & wellbeing
⚠️
Insufficient serotonin — low mood, anxiety, IBS & poor gut motility
Gut–Brain
Axis
Axis
5
Vagus Nerve Signalling
Gut serotonin activates the vagus nerve, sending healthy signals along the gut-brain axis to regulate mood, digestion and motility.
5
Disrupted Vagal Signalling
Low serotonin and gut inflammation impair vagus nerve communication, weakening gut-brain signalling.
Serotonin
Production
Production
4
Serotonin Synthesised
Tryptophan → 5-HTP → Serotonin (5-HT). The gut produces ~90–95% of the body's total serotonin supply.
4
Tryptophan Diverted
Inflammation reroutes tryptophan down the kynurenine pathway instead, cutting serotonin synthesis further.
EC Cell
Signal
Signal
3
EC Cells Stimulated
SCFAs stimulate enterochromaffin (EC) cells in the gut lining, activating the TPH1 enzyme — the key trigger for serotonin synthesis.
3
EC Cells Under-Stimulated
Without adequate SCFAs, EC cells receive weak signals. Inflammation suppresses TPH1 enzyme activity directly.
Microbiome
Activity
Activity
2
Microbiome Produces SCFAs
Diverse bacteria (Clostridia, Lactobacillus, Bifidobacterium) ferment fibre into short-chain fatty acids like butyrate.
2
Loss of SCFA-Producing Bacteria
Imbalanced microbiome lacks sufficient beneficial bacteria, drastically reducing SCFA output.
Tryptophan
Intake
Intake
1
Tryptophan Absorbed
Dietary tryptophan (eggs, turkey, nuts) is efficiently absorbed through a healthy gut lining.
1
Poor Tryptophan Absorption
Inflamed, permeable gut lining reduces absorption of tryptophan from food.