Muscle loss on Mounjaro: how to keep your muscle
Some of the weight you lose on a GLP-1 is lean mass, not fat. Enough protein plus regular strength training is the best-supported way to keep more muscle.
What the trials show
In the STEP 1 trial of semaglutide (Wegovy), body scans in a group of participants showed that of the weight lost, about 62% was fat and 38% was lean mass. Lean mass includes muscle, water and organs, and the 2025 advisory estimates this corresponds to about 20% of the weight lost being muscle. In the SURMOUNT-1 trial of tirzepatide (Mounjaro), fat made up most of the weight lost, but lean mass fell too.
Losing some lean mass is normal with any weight loss. The aim is to keep as much muscle as you can, because muscle supports strength, balance and your metabolism.
1. Eat enough protein
The advisory describes targets of 1.2 to 1.6 g per kg of body weight a day during weight loss, or about 80 to 120 g a day. With a small appetite, that means protein first at every meal and four small meals instead of two big ones. Work out your protein target.
2. Do strength training
The advisory says more protein alone is likely not enough without resistance exercise. It recommends strength training at least three times a week plus at least 150 minutes of moderate activity, like brisk walking, each week.
- Start simple: sit-to-stands from a chair, wall press-ups, step-ups, and resistance bands.
- Build up slowly: add a few reps or a heavier band every week or two.
- Cover the big muscles: legs, back, chest and arms, two or three times a week.
3. Track it, so you can see it
It's easy to under-eat protein without noticing. Logging meals for a couple of weeks shows your real average. SnapNosh shows the protein in a meal from one photo, so you can see each day whether you got enough.
Talk to your doctor before starting a new exercise programme if you have a health condition.
See the protein in every meal
SnapNosh shows the protein in a meal from one photo and tells you what's left for today. Made for life on a GLP-1.
Common questions
Do you lose muscle on Mounjaro?
Some of the weight lost on GLP-1 medicines is lean mass. In the STEP 1 semaglutide trial, about 38% of the weight lost in a scanned group was lean mass. Enough protein and strength training help keep more muscle.
How do I prevent muscle loss on Mounjaro?
Eat enough protein (about 80 to 120 g a day for many people) and do strength training at least three times a week, plus 150 minutes of moderate activity, as a 2025 expert advisory recommends.
Sources
- Nutritional priorities to support GLP-1 therapy for obesity (joint advisory, 2025)
- NHS: Tirzepatide (Mounjaro)
- NHS: Semaglutide (Wegovy, Ozempic)
This guide is general information about food and habits. It is not medical advice and doesn't replace advice from your doctor, pharmacist or dietitian. Ozempic and Wegovy are trademarks of Novo Nordisk; Mounjaro and Zepbound are trademarks of Eli Lilly. SnapNosh is not affiliated with them.