Muscle loss on a GLP-1: how to lose fat and keep your strength

Some of the weight you lose on a GLP-1 is lean mass, which includes muscle. In trials, lean mass made up about a quarter of the weight lost with tirzepatide and a little over a third with semaglutide, similar to weight loss through diet and lifestyle programs. Strength training two or three times a week, with enough protein at every meal, is a well-established way to protect it.

Reviewed by Darshan Patel, MD, Obesity medicine physician, on 2026-11-12. Next review 2027-05-11.

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Lose the fat, keep the strong

When you lose a lot of weight, you want to end up leaner and stronger, not just smaller. That's possible, and it starts with knowing what the scale doesn't show.

How much of the weight lost is muscle?

First, a quick translation. Body scans measure lean mass, which includes muscle but also organs, bone and water. So lean mass loss isn't the same thing as muscle loss.

• Tirzepatide (the medicine in Zepbound). In a body scan study within the SURMOUNT-1 trial, about 75% of the weight people lost was fat and about 25% was lean mass.
• Semaglutide (the medicine in Wegovy). In the STEP 1 trial, of an average 13.6 kg lost, 8.3 kg (62%) was fat and 5.3 kg (38%) was lean mass. Because muscle makes up about half of lean mass, a joint advisory from four medical and nutrition organizations estimates that about 20% of the weight lost was muscle.
• Compared with diet and lifestyle programs. A 2026 review of 20 trials found lean mass made up a similar share of the weight lost with GLP-1 medicines (about 25% to 35%) and with diet-and-lifestyle programs (about 26%). Programs that added strength training did best, at about 18%.

There's encouraging news too. Studies using MRI suggest the muscle changes are largely adaptive: muscle quality can improve, with less fat stored inside the muscle and better insulin sensitivity.

Why it's worth protecting

One review compared the lean mass lost on these medicines to a decade or more of normal aging. Muscle is what lets you climb stairs, carry the groceries and stay steady on your feet, and keeping muscle and strength as you get older helps protect against frailty. Researchers also think holding on to lean mass could make it easier to keep the weight off later.

Your muscle plan

1. Strength training, two to three times a week. Federal guidelines call for muscle-strengthening activity on at least 2 days each week. The joint advisory goes further for people on a GLP-1: strength training at least 3 times a week, plus at least 150 minutes of moderate aerobic activity. In studies of supervised strength programs lasting more than 10 weeks, men and women gained about 3 kg of lean mass and about 25% in strength.
2. Start where you are. Squats to a chair, wall push-ups, resistance bands and light dumbbells all count. The advisory recommends matching the plan to your fitness level so you can keep it up.
3. Protein at every meal. The advisory notes targets of about 1.2 to 1.6 grams per kilogram of body weight a day during weight loss, or a simpler 80 to 120 grams a day. See how much protein you need on a GLP-1 for easy foods and a sample day.
4. Do both. The advisory is clear that more protein alone is unlikely to protect muscle without structured strength training.
5. Track strength, not just weight. Simple tests like standing up from a chair or climbing stairs can help, especially for older adults, along with body composition measurements.

Muscle also matters if you ever stop your medicine. See stopping Wegovy or Zepbound without regaining and do I have to take a GLP-1 forever?

What about peptides sold for muscle?

You may see peptides marketed to build or protect muscle. Our peptide guides grade the evidence for each one, including sermorelin and MOTS-c. We don't prescribe peptides right now. For keeping muscle while you lose weight, strength training and protein are where the strongest evidence is. For more on staying strong as you age, see live well, age well.

Weight care that protects your muscle

At Aayu Well, an obesity medicine physician sees you by video and builds your weight plan with muscle in mind, with GLP-1 medicines when they're right for you. A registered dietitian turns your protein target into meals you'll enjoy. Your care team is a message away between visits, and your plan is built for keeping the weight off, not just taking it off.

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Good to know

• Older adults and people with more serious illness have a higher risk of sarcopenia, meaning too little muscle. Your physician will factor that in when planning your care.
• If you have heart, joint or balance concerns, ask your physician which kinds of strength work suit you before you start.
• The trials in this guide studied the brand-name medicines along with diet and activity advice. Results vary from person to person.

More physician-reviewed guides are in Learn, and our editorial policy explains how we choose sources and grade evidence.

Questions people ask

Can Aayu Well help me keep muscle while I lose weight?

Yes. Your obesity medicine physician plans your weight loss with muscle in mind, a registered dietitian helps you reach a protein target you can actually eat, and your care team checks in on your strength as well as the scale. We prescribe GLP-1 medicines when they're right for you. Most major insurance accepted, plus convenient cash pay options.

Is most of the weight I lose on a GLP-1 muscle?

No. Most of it is fat. In a body scan study from the SURMOUNT-1 trial, about 75% of the weight lost on tirzepatide was fat and 25% was lean mass. In STEP 1, about 62% of the weight lost on semaglutide was fat. And lean mass isn't all muscle: it also includes organs, bone and water.

Do I lose more muscle on a GLP-1 than on a diet?

Not by share of weight lost, according to a 2026 review of 20 trials. Lean mass made up a similar part of the weight lost with GLP-1 medicines and with diet-and-lifestyle programs. Programs that added strength training did best, with lean mass making up about 18% of the loss.

Do I need protein shakes to keep my muscle?

Not necessarily. Food comes first: fish, eggs, Greek yogurt, cottage cheese, beans and lentils are all good choices. Shakes and bars help some people reach their target. Protein works best alongside strength training, not instead of it.

What about peptides marketed for muscle?

Our peptide guides grade the evidence for each one, including sermorelin and MOTS-c. We don't prescribe peptides right now. For keeping muscle while you lose weight, strength training and enough protein have stronger evidence.

Sources

1. 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. Obesity Pillars. 2025;15:100181
2. Look M, et al. Body composition changes during weight reduction with tirzepatide in the SURMOUNT-1 study of adults with obesity or overweight. Diabetes Obes Metab. 2025
3. Eisa N, Barood O. Lean mass changes with incretin therapy versus lifestyle intervention: a systematic review and meta-analysis of randomised controlled trials. Diabetes Obes Metab. 2026;28(6):4818-4827
4. Neeland IJ, Linge J, Birkenfeld AL. Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies. Diabetes Obes Metab. 2024;26 Suppl 4:16-27
5. Locatelli JC, et al. Incretin-based weight loss pharmacotherapy: can resistance exercise optimize changes in body composition? Diabetes Care. 2024;47(10):1718-1730
6. HHS Office of Disease Prevention and Health Promotion: Physical Activity Guidelines for Americans, top 10 things to know