GLP-1Glucagon-like peptide-1
A gut hormone released when you eat that signals fullness to the brain.
GLP-1, glucagon-like peptide-1, is an incretin hormone released by cells in the intestine when food arrives. It prompts insulin release when glucose is rising, suppresses glucagon, slows the rate at which the stomach empties, and acts on appetite centres in the brain.
That combination is the body's own satiety system. Your own GLP-1 is released after eating and broken down within minutes by an enzyme called DPP-4, which is why the natural signal is short lived and why the drug versions are engineered to resist that breakdown and last for days.
It matters because understanding the natural hormone explains what the medicines are doing. They are not speeding up metabolism or blocking absorption; they are amplifying a signal you already produce, which is why the dominant effect is eating less rather than burning more.
It also explains the side effect profile. Slowed gastric emptying is part of the mechanism and also the reason nausea, early fullness and reflux are the most common complaints, and why anaesthetic and endoscopy teams now ask about these medicines before procedures.
The natural signal responds to food composition, modestly. Protein and fibre rich meals produce a larger and longer GLP-1 response than refined carbohydrate, which is part of why those foods are more filling.
That modest responsiveness is the basis of the natural GLP-1 booster category, which oversells it considerably. Eating protein and fibre is worth doing and is not equivalent to a prescription medicine that maintains the signal continuously.
In practice, GLP-1 is a hormone rather than a supplement, and the useful version of the advice is the same one our satiety entry gives: build meals around protein and fibre.