Over 90% of the body's serotonin is produced in the gut. The gut-brain axis is not a metaphor — it is a bidirectional communication network with direct implications for mood, cognition, and stress response.
The phrase 'gut feeling' turns out to be more literal than figurative. The gut-brain axis is a bidirectional communication network linking the enteric nervous system (the 'second brain' embedded in the gastrointestinal tract) with the central nervous system via the vagus nerve, the immune system, and the endocrine system. Over 90% of the body's serotonin is produced in the gut. The gut microbiome produces neurotransmitter precursors, short-chain fatty acids, and neuroactive compounds that directly influence brain function.
The enteric nervous system (ENS) is a network of approximately 500 million neurons embedded in the walls of the gastrointestinal tract — more neurons than the spinal cord. It regulates gut motility, secretion, and blood flow largely independently of the brain. Approximately 80–90% of vagal fibers carry signals from the gut to the brain — meaning the gut is sending far more information to the brain than the brain is sending to the gut.
Published: 2025-02-20 • Last updated: 2025-07-01 • By SaBio Science Team • Category: Gut-Brain Health
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