What is GLP-1, and what does it do in the body?
GLP-1 is a hormone released by cells in the small intestine after eating. It does three things at once: it triggers insulin only when glucose is high, it suppresses glucagon, and it slows the stomach emptying, while signalling fullness to the hypothalamus. The natural hormone breaks down within minutes, which is why the drugs are modified to last days.
The name is everywhere now, mostly as a drug. But it is a hormone that has been in everyone's body all along, and understanding it makes the news about the drugs much easier to read.
What is GLP-1 and where does the body make it?
GLP-1 stands for glucagon-like peptide-1. It is released by L-cells in the wall of the lower small intestine and colon when food arrives. It belongs to a family called the incretins — the system the gut uses to tell the pancreas and the brain that food has come in.
What does it do?
- Triggers insulin, but only when glucose is high. This matters enormously: it calls for insulin only when blood sugar warrants it, which is why this drug class causes far less hypoglycaemia than some older diabetes medicines.
- Suppresses glucagon, the hormone that tells the liver to release glucose. Damping it after a meal helps control blood sugar from the other side.
- Slows gastric emptying. Food stays in the stomach longer, so fullness lasts longer — and this is also where the nausea on these drugs comes from.
- Signals fullness to the brain, acting on receptors in the hypothalamus and brainstem, the areas that govern appetite.
Why can't the natural hormone be used as a drug?
Because it disappears too fast. GLP-1 released by the body is broken down by the enzyme DPP-4 within about two minutes — appropriate for a between-meals signal, useless as a medicine.
The drugs in this class are restructured to resist DPP-4 and to bind to albumin in the blood, which stretches their life from minutes to days and makes a weekly injection possible.
Where did the first drug come from?
From lizard venom. A compound called exendin-4, found in the saliva of the Gila monster, shares about half its structure with human GLP-1 but resists breakdown far better. It became the template for exenatide, the first approved drug of the class.
Can you raise your own GLP-1 with food?
Yes, but the scale of it needs stating honestly. Protein and fibre do stimulate GLP-1 release, and that is part of why a high-protein meal keeps you full longer.
The levels reached through food and the levels reached with a drug are far apart, though. Marketing that promises to "boost your natural GLP-1" is not wrong about the mechanism, but it is badly misleading about the size of the effect. Eating enough protein and fibre is worth doing for its own reasons — not as a cheap version of a medicine.
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