Weight care | 6 min read
How to Protect Muscle and Strength While Losing Weight on a GLP-1
Editorial draft — clinical review pending.
Short answer: Any significant weight loss includes some lean mass, and GLP-1 medicines are no exception. In a body scan substudy of tirzepatide, about three quarters of the weight lost was fat and one quarter was lean mass. You can limit muscle loss by doing strength training at least twice a week, eating enough protein, and telling your care team if you feel weaker. [1,2]
Key takeaways
- In the SURMOUNT-1 DXA substudy of 160 people, roughly 75% of weight lost was fat and 25% was lean mass. [1]
- Lean mass includes water, organs and connective tissue, not only muscle, so "25% muscle loss" overstates it.
- Federal guidelines call for muscle-strengthening activity at least two days a week plus regular aerobic activity. [2]
What the numbers actually say
DXA scans estimate fat, lean tissue and bone. In the SURMOUNT-1 substudy, people taking tirzepatide lost substantially more fat than lean mass, and the ratio was similar to what is seen with diet-based weight loss. [1] That is reassuring, but it is still an average. Women over 50, people who were already inactive, and anyone losing weight quickly may lose more muscle and should pay closer attention.
Muscle matters for more than looks. It supports balance, blood sugar control, bone strength and the ability to keep doing everyday tasks as you age.
Build a simple strength routine
The guideline is muscle-strengthening work on two or more days a week covering the major muscle groups, plus about 150 minutes a week of moderate aerobic activity such as brisk walking. [2] If that sounds like a lot, start smaller. Some activity is better than none.
A beginner week might look like this:
- Two 20-minute sessions of squats to a chair, wall push-ups, step-ups and resistance-band rows.
- Two or three brisk walks.
- Add a set or a little weight every week or two as it gets easier.
If you have joint pain, heart disease or another condition, ask your clinician what is safe first. A physical therapist or certified trainer can help you start correctly.
Eat to protect muscle
Reduced appetite makes it easy to fall short on protein. Put a protein source first at each meal, such as eggs, Greek yogurt, fish, chicken, tofu, beans or cottage cheese, and eat it before the rest of the plate. Ask your care team for a protein target based on your size and health. See our nutrition guide for more.
Track strength, not just weight
Signs worth noting:
- Getting up from a chair or the floor is harder.
- Stairs or carrying groceries feel more tiring.
- You can lift less in your usual workout.
- You feel weak, dizzy or exhausted most days.
These are reasons to contact your care team, not badges of fast progress. The plan may need a slower dose increase, more protein, or more support.
Frequently asked questions
Do GLP-1s cause muscle loss?
Weight loss from any cause includes some lean mass. GLP-1 studies show most of the loss is fat, and strength training plus protein can help limit muscle loss. [1]
How many days a week should I strength train?
At least two days a week, working all major muscle groups. [2]
Can I build muscle while losing weight?
Beginners often can, especially with regular resistance training and enough protein.
Next step
HerScripts weight care looks at strength and how you feel day to day, not just the scale. Learn about strength and body changes.
Sources
[1] Look et al., SURMOUNT-1 DXA substudy, 2025
[2] HHS Physical Activity Guidelines, questions and answers
Educational information, not personal medical advice. Care decisions require an individual clinical evaluation.