GLP-1 is the hormone underpinning the most significant advance in obesity medicine in decades. Understanding it demystifies Ozempic, Wegovy, Mounjaro, and Zepbound.
What Is GLP-1?
Glucagon-like peptide-1 is an incretin hormone released from the small intestine after eating. It stimulates insulin release, suppresses glucagon, slows gastric emptying, and critically — sends satiety signals to the hypothalamus (the brain's appetite centre).
Why It Matters for Obesity
In many people with obesity, the GLP-1 response to food is blunted — the satiety signal is weaker than in lean individuals. GLP-1 receptor agonists restore and amplify this signal continuously, reprogramming appetite downward.
The GLP-1 Drugs (2025)
- Semaglutide (Ozempic, Wegovy): Weekly injection. 14.9% body weight loss in STEP trials.
- Tirzepatide (Mounjaro, Zepbound): Dual GLP-1/GIP agonist. 20.9% weight loss in SURMOUNT-1.
- Liraglutide (Saxenda): Daily injection. Older, less potent. Largely superseded.
- Oral semaglutide (Rybelsus): Lower bioavailability than injections.
- Retatrutide: Triple agonist in Phase 3 trials — up to 24% weight loss in early data.
Natural GLP-1 Boosters
Soluble fibre (oats, legumes, chia seeds), whey protein, olive oil, and fermented foods stimulate natural GLP-1 release. Effects are far more modest than medications but meaningful — and partly explain why Mediterranean and Sirtfood diets support weight loss.