Part of our Workout Recovery guide library.
Short answer: Yes, some of the weight lost on a GLP-1 medication is muscle. In the STEP 1 trial of semaglutide, about 38% of the weight lost was lean mass, which works out to roughly 20% of the total being muscle. That is similar to other ways of losing a lot of weight quickly. The two steps with the most support for keeping muscle are strength training at least 3 times a week and eating enough protein. A joint advisory from four U.S. nutrition and obesity medicine organizations notes that more protein alone is unlikely to be enough without resistance training.
GLP-1 medications such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) cut appetite so much that many people eat far less than before. That helps with weight, but it can also mean losing muscle along with fat. Here is how much muscle loss the trials found, who is most at risk, and what the 2025 joint nutrition advisory recommends.
What you'll learn
- How much of the weight lost on GLP-1 medications is muscle
- Who is most likely to lose muscle
- How much strength training and protein the joint advisory recommends
- What to keep doing during and after treatment
Do GLP-1 medications cause muscle loss?
They cause weight loss, and weight loss from any method usually includes some muscle. The prescribing information for Wegovy and Zepbound notes that both lower body weight with greater fat loss than lean mass loss (Wegovy prescribing information; Zepbound prescribing information). Lean mass still goes down, though. In the STEP 1 trial, people lost an average of 13.6 kg (about 30 pounds), and 5.3 kg (38%) of that was lean body mass, which includes muscle and other non-fat tissue (Mozaffarian et al., 2025).
| What the research found | Details |
|---|---|
| STEP 1 (semaglutide) | 38% of weight lost was lean mass; since muscle is about half of lean mass, roughly 20% of the total was muscle (Mozaffarian et al., 2025) |
| SURMOUNT 1 (tirzepatide) | Lean mass fell by 8.5 percentage points across doses (Mozaffarian et al., 2025) |
| Modeling, without structured strength training | Muscle made up about 10% to 15% of weight lost in women and 20% to 25% in men (Mozaffarian et al., 2025) |
These losses track with how much weight is lost and are similar to those seen after bariatric surgery or very low-calorie diets (Mozaffarian et al., 2025).
Who is most at risk?
How much lean mass you lose depends on how sharply you cut calories, how fast you lose weight, and whether you do strength training. Eating too little protein because of a smaller appetite can add to muscle loss, especially for people who are older, in perimenopause or menopause, have lower testosterone, are inactive, or do no resistance training (Mozaffarian et al., 2025).
Bone is affected too: losing 14% or more of body weight over 3 to 4 months has been linked to significant bone loss (Mozaffarian et al., 2025). Strength training helps protect both.
Step 1: Strength training at least 3 times a week
The joint advisory recommends that GLP-1 medications be prescribed together with a structured exercise program, aiming for strength training at least 3 times a week plus at least 150 minutes of moderate aerobic exercise a week, adjusted to your fitness level (Mozaffarian et al., 2025).
- Work the big muscle groups: legs, hips, back, chest and arms, using weights, machines, bands or your own body weight.
- Progress gradually: add a little weight or a few repetitions as exercises get easier.
- Fuel and recover: eating very little makes workouts harder, so plan a meal or snack with protein around training. If you are sore, see should you work out with sore muscles?
- Get guidance if you are new to it. A physical therapist or certified trainer can tailor a plan, especially if you have joint problems or have not trained before.
Step 2: Eat enough protein
The recommended dietary allowance for adults is 0.8 grams of protein per kilogram of body weight a day, and higher targets of 1.2 to 1.6 g/kg have been proposed during active weight loss (Mozaffarian et al., 2025). It is not settled whether people with obesity should calculate this from their actual weight or an adjusted weight, so ask your clinician or a registered dietitian for your number (Mozaffarian et al., 2025).
| Body weight | 0.8 g/kg (general RDA) | 1.2–1.6 g/kg (proposed during weight loss) |
|---|---|---|
| 60 kg (132 lb) | 48 g a day | 72–96 g a day |
| 80 kg (176 lb) | 64 g a day | 96–128 g a day |
| 100 kg (220 lb) | 80 g a day | 120–160 g a day |
When your appetite is small, choose foods that pack protein into small portions, such as fish, eggs, Greek yogurt, cottage cheese, and nuts, seeds and nut butters. Some people meet their target with protein shakes, bars or fortified foods (Mozaffarian et al., 2025).
Protein is not a substitute for training: the advisory stresses that eating more protein alone is likely not enough to preserve muscle without structured resistance training (Mozaffarian et al., 2025).
Step 3: Don't neglect the rest of your nutrition
Eating much less makes it harder to get enough vitamins and minerals, and the advisory recommends micronutrient or protein supplementation as needed, based on an assessment by your care team (Mozaffarian et al., 2025). If you feel unusually tired, see does Ozempic make you tired?
How to tell if you are losing muscle
The scale cannot tell fat from muscle. Clinicians can measure body composition, and simple tests such as how many times you can stand up from a chair, how quickly you climb stairs, or a timed walk can show changes in strength, especially in older adults (Mozaffarian et al., 2025). Noticing that everyday tasks, such as carrying groceries or climbing stairs, are getting harder is worth mentioning to your provider.
What about after you stop the medication?
Many people stop GLP-1 medications: an estimated 50% to 67% within the first year. After stopping, regaining weight is common, with up to two-thirds of the lost weight regained within a year (Mozaffarian et al., 2025). Keeping up strength training, protein-rich meals and regular activity matters during treatment and afterward. Talk to your prescriber before stopping, and ask about nutrition support for the transition.
Common myths (quick reality check)
Myth: GLP-1 medications only burn fat. Reality: They cause greater fat loss than lean mass loss, but in one major semaglutide trial 38% of the weight lost was lean mass.
Myth: A high-protein diet is enough to protect muscle. Reality: The joint advisory says more protein alone is likely inadequate without structured resistance training.
Myth: Muscle loss is only a concern for older adults. Reality: Older adults are at higher risk, but anyone losing weight quickly without strength training can lose muscle.
Frequently asked questions (FAQ)
Do GLP-1 medications cause muscle loss?
Some of the weight lost is muscle. In the STEP 1 trial of semaglutide, 38% of the weight lost was lean mass, roughly 20% of the total being muscle. This is similar to other ways of losing a lot of weight quickly.
How do I prevent muscle loss on Ozempic or Zepbound?
Strength train at least 3 times a week, add at least 150 minutes of moderate aerobic activity, and eat enough protein. Protein alone is unlikely to be enough without resistance training.
How much protein should I eat on a GLP-1?
The general RDA is 0.8 g per kg of body weight a day, and 1.2 to 1.6 g/kg has been proposed during weight loss. Ask your clinician or a dietitian which body weight to use for your target.
What are good protein sources when my appetite is small?
Fish, eggs, Greek yogurt, cottage cheese, and nuts, seeds and nut butters pack protein into small portions. Protein shakes, bars or fortified foods can help fill gaps.
Is muscle loss on GLP-1 medications permanent?
Muscle can be rebuilt with resistance training and enough protein, but it is easier to protect it as you go than to regain it later.
Should I keep strength training after stopping a GLP-1?
Yes. Weight regain is common after stopping, and keeping up strength training, protein-rich meals and regular activity supports your muscle during and after treatment.
Related guides
- What to eat after a workout
- GLP-1 supplements: do they work?
- Does Ozempic make you tired?
- Should you work out with sore muscles?
- What helps sore muscles after a workout?
- How long does DOMS last?
Disclaimer and when to seek help
This article is for general education and is not medical advice. It does not replace advice from the clinician who prescribes your medication, and you should not start, stop or change any medication without talking to them. Check with your provider before starting a new exercise program, especially if you have heart, joint or kidney problems. These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. Ozempic, Wegovy, Mounjaro and Zepbound are registered trademarks of their respective owners; OurJrney is not affiliated with them.
References
- Mozaffarian D, et al. "Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society." American Journal of Clinical Nutrition, 2025;122(1):344-367. doi:10.1016/j.ajcnut.2025.04.023
- Wegovy (semaglutide) prescribing information. DailyMed, U.S. National Library of Medicine. dailymed.nlm.nih.gov
- Zepbound (tirzepatide) prescribing information. DailyMed, U.S. National Library of Medicine. dailymed.nlm.nih.gov
