What Is GLP-1? The Gut Hormone the Weight-Loss Medicines Copy

GLP-1 is a hormone your gut makes every time you eat. Cells in the lining of the small intestine and colon release it when food arrives, and it does three things: tells the pancreas to release insulin in proportion to the sugar coming in, slows the stomach, and signals to the brain that a meal is under way.^{1, 2} It lasts one to two minutes in the blood before an enzyme breaks it down, which is one reason fullness fades a few hours after eating.^{2, 3} The medicines prescribed in the UK for weight management and type 2 diabetes, tirzepatide (Mounjaro), semaglutide (Wegovy, Ozempic) and liraglutide (Saxenda), are engineered copies of this hormone, built to resist that enzyme and hold the signal on for a day or a week rather than minutes.⁴

• What it is: glucagon-like peptide-1, a peptide hormone of 30 amino acids cut from the same precursor as glucagon
• Where it comes from: L cells in the lining of the small intestine and colon, released by protein, fat, carbohydrate and fermented fibre
• Food against medicine: a meal raises it severalfold for an hour or two; the medicines hold the receptor active all week

Sources checked on 29 October 2026.

What does GLP-1 stand for, and is it a peptide?

GLP-1 stands for glucagon-like peptide-1. It is a peptide: a short chain of amino acids, 30 of them in the main active form.¹ The "glucagon-like" part is a family name. Your body makes one long precursor protein, proglucagon, and cuts it differently in different tissues. In the pancreas it becomes glucagon, the hormone that raises blood sugar between meals; in the gut the same precursor is cut into GLP-1 and GLP-2.¹ When people say "GLP-1" about a medicine, they mean a GLP-1 receptor agonist: a molecule shaped to fit the hormone's receptor and switch it on.

Where is GLP-1 made, and why does food release it?

By L cells, specialised hormone-producing cells scattered along the lining of the small intestine and colon, most densely towards the far end.^{1, 5} They face into the gut and carry sensors for amino acids, fatty acids and glucose, and release GLP-1 into the blood in proportion to what they sense. Protein and fat are strong triggers, and a bigger meal releases more than a smaller one.² Fibre works later and lower down: bacteria in the colon ferment it into short-chain fatty acids, which the same cells detect.⁵ It was identified as a human incretin, a gut hormone that boosts insulin after a meal, in 1987.⁶

What does GLP-1 do in the body?

Three things, all of them about managing a meal. It tells the pancreas to release insulin only while sugar is arriving, which is why GLP-1 on its own rarely causes low blood sugar.¹ It slows the stomach's emptying, which is partly why a meal keeps you full. And it acts on the appetite centres of the brain: when researchers infused GLP-1 into 20 healthy young men around mealtimes, they reported more fullness and ate about 12% less at lunch.⁷ The enzyme DPP-4 breaks it down within minutes of release, and a few hours after eating the signal has faded and hunger returns.³

Which UK medicines copy GLP-1?

Three. Semaglutide and liraglutide are modified versions of the hormone that resist DPP-4 and bind to proteins in the blood, so one injection keeps the receptor active for a day (liraglutide) or a week (semaglutide).⁴ Tirzepatide is a single molecule that activates the GLP-1 receptor and the receptor for a second gut hormone, GIP, also for a week at a time.⁴ At that level the three effects run continuously: in one manufacturer-funded trial of 30 adults, semaglutide cut intake by about a quarter without any dietary instruction, and in the manufacturer-funded STEP 1 trial of 1,961 adults, semaglutide reduced body weight by a mean 14.9% over 68 weeks against 2.4% on placebo.^{8, 9} All three are prescription medicines; whether one suits you is your prescriber's decision, and the NHS pages for tirzepatide, semaglutide and liraglutide cover the rest.^{10, 11, 12} How Mounjaro works covers the tirzepatide mechanism and GLP-1 side effects the stomach.

Is GLP-1 the same as Ozempic?

No. GLP-1 is the hormone; Ozempic is a brand of semaglutide, a medicine that copies it. The class is called "GLP-1s" in conversation and "GLP-1 receptor agonists" on paper. Everyone makes GLP-1, so "taking GLP-1" is not something a food or a capsule can offer. And the medicine is not the hormone: it holds the receptor active at a level and for a duration no meal produces.

What is the difference between GLP-1 and GLP-2?

Same precursor, same cells, released together, different jobs. GLP-2 acts on the gut lining itself: it increases blood flow to the intestine, helps the lining grow and repair, and improves nutrient absorption.¹³ It has little effect on appetite or insulin, and the one GLP-2 medicine in use is for people with short bowel syndrome, not for weight. When a forum post says "GLP-2" about a weight-loss injection, it nearly always means the GIP part of tirzepatide, a different hormone again, released higher up the small intestine.⁴

Can you increase GLP-1 naturally?

Yes, within limits. Protein at a meal raises it most reliably; soluble fibre from oats, beans and lentils may add to it through fermentation (the evidence is mixed); unsaturated fats from olive oil, nuts and avocado help; and eating the vegetables and protein before the carbohydrate on the same plate produced a higher GLP-1 response to the same food in a crossover trial of 16 adults with type 2 diabetes.^{5, 14, 15, 16} In a four-day feeding study of 12 women, a high-protein diet raised GLP-1 after dinner and 24-hour fullness compared with a normal-protein one.¹⁴ The limit is size and duration. A meal raises GLP-1 severalfold for an hour or two and then DPP-4 clears it; the medicines hold the receptor active at pharmacological levels for a week.^{2, 4} Food makes each meal more filling; it does not do what the injection does. Which foods increase GLP-1 has the food list, do GLP-1 supplements work the ingredients, and what is the GLP-1 diet the meals. On the medicine, a small appetite still has to carry the same protein and fibre (living well on Mounjaro); after it, your own GLP-1 is what you have (what happens when you stop).

What we don't know

Whether food-released GLP-1 acts mainly through the blood or through gut nerves is debated, since little intact hormone reaches the circulation.^{1, 2} No trial has tested whether eating to raise your own GLP-1 changes weight. A single dose of fermentable fibre raised short-chain fatty acids but not GLP-1 in a 25-person crossover study; longer intake is untested.¹⁶

Frequently asked questions

Is GLP-1 bad for you?

The hormone is not: you have made it after every meal of your life. The question usually means the medicines, whose common side effects are the hormone's jobs overdone; GLP-1 side effects: what is common and what helps sets them out.

Which GLP-1 medicines are available for weight loss in the UK?

Semaglutide (Wegovy), liraglutide (Saxenda) and tirzepatide (Mounjaro) are licensed for weight management in the UK; Ozempic is semaglutide licensed for type 2 diabetes.

How does GLP-1 work?

It is released from the gut lining when food arrives and acts on receptors in the pancreas, the stomach and the brain: insulin goes up while sugar is arriving, the stomach slows, and you feel full.^{1, 7}

How long does GLP-1 last in the body?

Your own: one to two minutes in the blood before DPP-4 breaks it down, with a meal's release tailing off over a few hours.^{2, 3} The medicines last a day (liraglutide) or a week (semaglutide, tirzepatide).

Does GLP-1 burn fat?

No. It reduces how much you want to eat and steadies blood sugar; any fat loss follows from eating less. The same is true of the medicines, which is why protein and resistance training matter on them.

Sources

1. Holst JJ. The physiology of glucagon-like peptide 1. Physiological Reviews, 2007. Narrative review; funding not stated on PubMed. PubMed 17928588.
2. Müller TD, et al. Glucagon-like peptide 1 (GLP-1). Molecular Metabolism, 2019. Consensus review; funding not stated on PubMed. PubMed 31767182.
3. Deacon CF, et al. Both subcutaneously and intravenously administered glucagon-like peptide I are rapidly degraded from the NH2-terminus in type II diabetic patients and in healthy subjects. Diabetes, 1995. Clinical pharmacology study, 8 adults with type 2 diabetes and 8 healthy adults; funding not stated on PubMed. PubMed 7657039.
4. Drucker DJ. Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metabolism, 2018. Narrative review; funding not stated on PubMed. PubMed 29617641.
5. Gribble FM, Reimann F. Function and mechanisms of enteroendocrine cells and gut hormones in metabolism. Nature Reviews Endocrinology, 2019. Narrative review; funding not stated on PubMed. PubMed 30760847.
6. Kreymann B, et al. Glucagon-like peptide-1 7-36: a physiological incretin in man. Lancet, 1987. Infusion study, 7 volunteers; funding not stated on PubMed. PubMed 2890903.
7. Flint A, et al. Glucagon-like peptide 1 promotes satiety and suppresses energy intake in humans. Journal of Clinical Investigation, 1998. Randomised crossover infusion study, 20 healthy men; funding not stated on PubMed. PubMed 9449682.
8. Blundell J, et al. Effects of once-weekly semaglutide on appetite, energy intake, control of eating, food preference and body weight in subjects with obesity. Diabetes, Obesity and Metabolism, 2017. Randomised crossover trial, 30 adults, 12 weeks; manufacturer-funded. PubMed 28266779.
9. Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine, 2021. Randomised trial (STEP 1), 1,961 adults, 68 weeks; manufacturer-funded. PubMed 33567185.
10. NHS. Tirzepatide. Page last reviewed 15 May 2026. nhs.uk.
11. NHS. Semaglutide. Page last reviewed 15 May 2026. nhs.uk.
12. NHS. Liraglutide. Page last reviewed 15 May 2026. nhs.uk.
13. Drucker DJ, Yusta B. Physiology and pharmacology of the enteroendocrine hormone glucagon-like peptide-2. Annual Review of Physiology, 2014. Narrative review; funding not stated on PubMed. PubMed 24161075.
14. Lejeune MP, et al. Ghrelin and glucagon-like peptide 1 concentrations, 24-h satiety, and energy and substrate metabolism during a high-protein diet. American Journal of Clinical Nutrition, 2006. Randomised crossover feeding study, 12 women, 4 days per diet; funding not stated on PubMed. PubMed 16400055.
15. Shukla AP, et al. Carbohydrate-last meal pattern lowers postprandial glucose and insulin excursions in type 2 diabetes. BMJ Open Diabetes Research and Care, 2017. Randomised crossover trial, 16 adults with type 2 diabetes, three test meals; no competing interests declared. PubMed 28989726.
16. Rahat-Rozenbloom S, et al. Acute increases in serum colonic short-chain fatty acids elicited by inulin do not increase GLP-1 or PYY responses but may reduce ghrelin in lean and overweight humans. European Journal of Clinical Nutrition, 2017. Randomised crossover study, 25 adults, single doses; no conflicts declared. PubMed 27966574.

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This article is general information, not medical advice. Tirzepatide, semaglutide and liraglutide are prescription medicines: whether one is suitable for you is a decision for your prescriber, and nothing here replaces their advice.