The enteric nervous system (ENS) — embedded in the lining of your gut — contains over 500 million neurons, more than the spinal cord. It communicates bidirectionally with the brain via the vagus nerve. Scientists call it the 'second brain' because it can function completely independently of the central nervous system.
The Gut-Brain Axis
This is not metaphor — it is a real bidirectional signalling network involving neurons, hormones, and immune cells. About 90% of serotonin is produced in the gut, not the brain. A disrupted gut microbiome directly affects mood, cognition, and stress resilience.
Leaky Gut and Neuroinflammation
When tight junctions in the gut lining break down (intestinal permeability), bacterial endotoxins (LPS) enter the bloodstream, trigger systemic inflammation, and cross the blood-brain barrier — causing neuroinflammation linked to depression, anxiety, and cognitive decline.