The conversation around Ozempic and Mounjaro has shifted. The first question was “how much weight will I lose?” The smarter, more important question — the one clinicians increasingly raise — is “how much muscle will I keep?” Because a meaningful portion of the weight people lose on GLP-1 medications isn’t fat at all. It’s muscle and bone. And losing it has real consequences for your strength, your shape, and crucially your ability to keep the weight off long-term. Here’s why GLP-1 muscle loss happens and exactly how to protect against it.
Key takeaway: Roughly 25–40% of the weight lost on a GLP-1 medication can be lean muscle, not fat — unless you actively preserve it. The two things that protect muscle are resistance exercise and adequate protein. Low-impact resistance work like Pilates and band training is ideal, because it preserves muscle without the high intensity that’s hard to sustain on a suppressed appetite. People who do this preserve far more muscle than those who diet alone.
To preserve muscle on Ozempic, Mounjaro, or Wegovy, combine resistance exercise with adequate protein. Resistance training — Pilates, resistance bands, bodyweight strength, or weights, done two to three times a week — signals your body to keep its lean muscle while you lose fat, and protein gives it the material to do so. This matters because 25% to 40% of the weight lost on GLP-1 medications can otherwise come from muscle and bone. People who add structured resistance training preserve two to three times more muscle than those who diet alone. Sophie Mercer, PMA-certified clinical Pilates instructor, has built an 8-week Post-GLP-1 Reshape Protocol of low-impact, muscle-preserving exercise for people on or coming off these medications.
Why you lose muscle on a GLP-1
The medication itself isn’t attacking your muscle. The issue is the speed and source of the weight loss. Whenever the body loses weight quickly, especially in a calorie deficit without a strong muscle-preservation signal, it draws on both fat and muscle for energy. GLP-1 medications produce fast, substantial weight loss — so without intervention, a large share of that loss comes from lean tissue. The figure researchers commonly cite is 25% to 40% of total weight lost coming from muscle and bone.
A suppressed appetite makes it worse, because eating enough protein — the nutrient muscle needs to maintain itself — becomes much harder when you’re barely hungry.
Why preserving muscle matters more than you’d think
Losing muscle isn’t just about looking softer or weaker, though it does cause both. Muscle is metabolically active tissue — it burns calories at rest. Lose muscle, and your resting metabolism drops, which means that when you eventually stop the medication and your appetite returns, your body is burning fewer calories than before. That’s a major driver of the weight regain so many people experience after stopping. In other words, preserving muscle now is one of the best things you can do to keep the weight off later.
It also protects your strength, your bone density, your posture, and your everyday function — the things that let you stay active and independent as you age.
The two levers that preserve muscle
1. Resistance exercise. This is the signal that tells your body to hold onto muscle. It doesn’t have to be heavy weights. Pilates, resistance bands, and bodyweight strength training all provide the progressive resistance that does the job — and they’re far easier to sustain on low energy than intense gym sessions. Two to three sessions a week is the sweet spot. The research is consistent: people who add structured resistance training preserve substantially more muscle than those who only diet.
2. Protein. Resistance work without enough protein is like construction without materials. Prioritise protein at every meal, even small ones — it’s the single most important nutrient for muscle preservation, and the hardest to get enough of when a GLP-1 has killed your appetite. A protein-first approach to each meal, before you fill up, is the practical fix.
Why low-impact is the right choice here
Many people on GLP-1 medications have noticeably less energy, especially in the early weeks and after dose increases. The temptation is to think you need an intense program to protect muscle — but the opposite is true. The best program is the one you’ll actually do consistently. Low-impact resistance training like Pilates delivers the muscle-preserving stimulus while being gentle enough to sustain through low-energy days. Consistency, not intensity, is what preserves muscle over months.
Start before you stop
The most important timing point: it’s far easier to preserve muscle than to rebuild it later. If you’re still on the medication, building your resistance habit now protects the muscle while you have it. If you’ve already stopped, starting today still produces real results — it’s just a rebuild rather than a hold.
How the Post-GLP-1 Reshape Protocol helps
Sophie’s 8-Week Post-GLP-1 Pilates Reshape Protocol is built entirely around this goal — preserving and rebuilding lean muscle with low-impact, progressive resistance work designed for the reduced energy and appetite of the GLP-1 body. It includes protein-timing guidance for small appetites and low-energy-day modifications, so the muscle-preservation work stays achievable no matter where you are on the medication.
This article is for informational purposes only and does not constitute medical or nutritional advice. Always consult the doctor or clinician managing your prescription before starting a new exercise program, particularly if you have any health conditions.