The GLP-1 pathway starts after eating.
Enteroendocrine cells in the small intestine detect nutrients and put out GLP-1, a 30-amino-acid peptide. The signal acts on three main targets: the pancreas (to increase insulin secretion), the stomach (to slow gastric emptying), and the brain (to reduce hunger and increase satiety).
The route matters. GLP-1 reaches the brain through two channels at once. One is neural: the vagus nerve fires a direct signal from gut to brainstem. The other is hormonal: GLP-1 enters the bloodstream and crosses into the brain at regions where the blood-brain barrier thins.
The body's own signal clears in about two minutes. That speed is a feature. The body wants flexible signals, not permanent ones. Hunger returns when the signal fades, and the next meal triggers a fresh cycle.
GLP-1 peptides like semaglutide are engineered copies that resist that breakdown. The signal holds for days instead of minutes. Same receptor lock. Stronger signal. Longer hold. The result is sustained satiety and improved glucose control through a pathway the body already built.