GLP-1 Medication: Keep the Muscle
GLP-1 medicines make eating less far easier. Protecting the muscle underneath still takes work: enough protein, and lifting.
- In their headline trials, semaglutide and tirzepatide cut bodyweight by around 15% and up to about 20% over roughly 68 to 72 weeks.
- In a body-scan substudy, lean mass made up roughly two-fifths of the weight lost on semaglutide.
- Enough protein and resistance training are what protect muscle in any deficit, and matter more when appetite is low.
- Side effects and dosing are for your prescriber.
What the drugs do
Semaglutide and tirzepatide are among the most effective weight-loss treatments ever tested. In their headline trials, people on the top doses lost around 15% (semaglutide) and up to about 20% (tirzepatide) of their bodyweight over roughly 68 to 72 weeks, against a few percent on placebo. They work largely by turning appetite down, so eating less stops being a daily fight.
What goes with the fat
Not all of that weight is fat. In a body-scan substudy of the semaglutide trial, lean mass made up roughly two-fifths of the weight lost. Some lean loss comes with any large weight loss, and lean mass is not all muscle, but with appetite this quiet it is easy to under-eat protein by accident and give your body no reason to hold on to muscle it is carrying.
What protects it
The levers are the same ones that protect muscle in any deficit: enough protein, and resistance training that makes your muscles work. In dieting older adults, adding resistance training preserved lean mass better than dieting with aerobic exercise alone, and protein matters more, not less, when total intake is low. Lift two or three times a week and make protein the first thing on the plate.
What this is not
This is coaching, not medical advice. Dose changes, side effects such as persistent vomiting, or struggling to eat or drink enough are for your prescriber.
- Swelling of your face, lips, tongue or throat, or sudden difficulty breathing, after a dose
- Vomiting or diarrhoea that won't settle, or you can't keep fluids down
- Severe pain in your stomach or back that won't go away: call NHS 111 the same day
- A sudden change in your eyesight: call NHS 111
- Signs of dehydration: dizziness, a dry mouth, or passing little urine
- Yellowing of your skin or the whites of your eyes
Tell Kriterion you take a GLP-1 or appetite-reducing medicine and it sets protein at the top of your goal's range, and its coach stops reading a steep deficit or a stall as the usual warning signs.
References
- Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. The New England Journal of Medicine, 2021;384(11):989-1002.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. The New England Journal of Medicine, 2022;387(3):205-216.
- Cava E, Yeat NC, Mittendorfer B. Preserving healthy muscle during weight loss. Advances in Nutrition, 2017;8(3):511-519.
- Villareal DT, Aguirre L, Gurney AB, et al. Aerobic or resistance exercise, or both, in dieting obese older adults. The New England Journal of Medicine, 2017;376(20):1943-1955.
Last reviewed 28 Sep 2026 · Next review due Sep 2029
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