GLP-1 Muscle Loss: What the Research Shows and How to Protect Your Muscle

Key takeaways

• Any meaningful weight loss, whether from diet, surgery, or medication, includes some loss of lean mass along with fat. GLP-1 medications are no exception.
• "Lean mass" is not the same as muscle. It also includes water, organs, and other non-fat tissue, so lean mass figures overstate true muscle loss.
• Most of the weight lost in GLP-1 studies has been fat, but how much lean mass is lost varies between people and studies.
• Adequate protein and regular strength training are the two best-supported ways to help protect muscle while losing weight.
• Older adults, women after menopause, and anyone eating very little because of reduced appetite should pay closer attention, and a clinician can help set personal targets.

About the research in this article

About the research: The body-composition results described below come from studies of FDA-approved, brand-name products: Wegovy (semaglutide), Zepbound (tirzepatide), and Saxenda (liraglutide). Compounded versions of semaglutide and tirzepatide are not FDA-approved, and the FDA does not review compounded drugs for safety, effectiveness, or quality before they are marketed (FDA; FDA). These results cannot be assumed to apply to compounded versions (FDA). The nutrition and exercise guidance in this article applies to weight loss generally, not to any specific product.

Do GLP-1 medications cause muscle loss?

Yes, some, but the full answer is more nuanced than many headlines suggest. When you lose weight by any method, your body loses a mix of fat and lean tissue. GLP-1 medications reduce appetite and food intake, so they produce the same kind of mixed loss that a calorie-reduced diet does.

The concern is reasonable. Muscle supports strength, balance, metabolic health, and independence as you age. But it helps to understand what studies actually measured before drawing conclusions.

Lean mass is not the same as muscle

Most studies measure body composition with a DXA scan, which divides the body into fat mass, bone, and "lean mass." Lean mass includes skeletal muscle, but also water, organs, and connective tissue. A 2025 joint advisory from four obesity and nutrition societies notes that muscle makes up about half of lean mass, so a lean mass figure is an imperfect stand-in for muscle loss (Mozaffarian et al., 2025).

What the studies found

• Wegovy (semaglutide 2.4 mg): In a body-composition substudy of the STEP 1 trial, roughly 38% of the weight lost was lean mass and about 62% was fat, as summarized by the 2025 joint advisory. The advisory estimates this corresponds to about 20% of total weight lost being muscle (Mozaffarian et al., 2025; Wilding et al., 2021).
• Zepbound (tirzepatide): In a DXA substudy of SURMOUNT-1 with 160 participants, about 75% of the weight lost was fat and about 25% was lean mass after 72 weeks. Fat mass fell by about a third while lean mass fell by about 11%. The fat-to-lean ratio was similar in the placebo group, which lost far less weight overall (Look et al., 2025).

These were separate trials with different designs and participants, so they cannot be used to say one medication is better for muscle than the other. A 2024 review found the share of weight lost as lean mass ranged widely across GLP-1 studies, from about 15% or less in some to 40% or more in others, depending on the drug, population, and how body composition was measured (Neeland et al., 2024).

Is losing some lean mass always harmful?

Not necessarily. People with obesity often carry extra lean mass to support a larger body, and some of it is expected to decrease as weight comes down. Small MRI studies of liraglutide and tirzepatide found that muscle volume decreased roughly in line with the amount of weight lost, while fat stored inside muscle tissue also decreased, which may mean better muscle quality (Neeland et al., 2024).

That evidence is limited. The studies were small, most trials were not designed to measure strength or physical function, and researchers are still studying how these medications affect muscle quality over time. The practical takeaway is to take muscle seriously without assuming the worst.

Who should pay closer attention?

Losing some lean mass matters more for people who have less muscle to spare. That includes:

• Adults over about 60, since muscle mass and strength naturally decline with age.
• Women in perimenopause and after menopause, when lean mass tends to start declining. Our guide to menopause weight gain explains these changes.
• People eating very little because of a strong appetite reduction or side effects such as nausea.
• People losing weight very quickly or losing a large amount of weight.
• People who are not physically active or who have a condition that limits exercise.

How to protect muscle while taking a GLP-1

The 2025 joint advisory names adequate protein and strength training as core priorities for anyone using GLP-1 therapy (Mozaffarian et al., 2025). Neither is complicated, but both take intention when your appetite is lower than usual.

1. Make protein a priority at every meal

The standard recommended intake for adults is 0.8 grams of protein per kilogram of body weight per day. The joint advisory notes that higher targets, around 1.2 to 1.6 g/kg per day, have been proposed during active weight loss. It also suggests a simpler absolute target of about 80 to 120 grams per day may be easier to follow, and advises against long-term intake at or above 2 g/kg per day (Mozaffarian et al., 2025).

Practical ways to get there when you are not very hungry:

• Eat the protein on your plate first.
• Spread protein across meals instead of saving most of it for dinner.
• Choose protein-dense foods such as Greek yogurt, eggs, cottage cheese, fish, poultry, tofu, tempeh, lentils, and beans.
• Use a protein shake when a full meal is not realistic, especially on days when nausea makes solid food hard.

Your ideal target depends on your size, age, activity level, and kidney health. Clinicians sometimes base the target on a goal or adjusted body weight rather than current weight. If you have kidney disease, talk with your clinician before increasing protein.

2. Strength train at least two to three days a week

Resistance training gives muscle a reason to stay. U.S. guidelines recommend muscle-strengthening activity that works all major muscle groups on at least two days a week for all adults (CDC). For people using GLP-1 therapy, the joint advisory goes further, recommending structured strength training at least three times a week plus at least 150 minutes of moderate aerobic activity (Mozaffarian et al., 2025).

You do not need a gym. Bodyweight squats, push-ups against a wall or counter, resistance bands, and light dumbbells all count. The key is gradual progression: slowly adding repetitions, resistance, or sets as exercises become easier. If you are new to strength training or have joint, heart, or balance concerns, a physical therapist or qualified trainer can help you start safely.

3. Combine medication with exercise rather than relying on either alone

Direct evidence on exercise during GLP-1 therapy is still limited, but one randomized trial offers a useful signal. After an initial low-calorie diet, adults with obesity were assigned to exercise, liraglutide 3.0 mg (the product sold as Saxenda), both, or placebo for one year. The combination group reduced body-fat percentage by about twice as much as either treatment alone, and only the combination improved cardiorespiratory fitness (Lundgren et al., 2021). The trial focused on weight maintenance and body fat rather than muscle specifically, so it supports exercise as a partner to medication rather than proving a muscle-sparing effect.

4. Avoid eating too little

Reduced appetite is how GLP-1 medications work, but very low food intake makes it harder to get enough protein and nutrients. If you regularly skip meals because you are not hungry, or side effects are limiting what you can eat, tell your clinician. Our guide to GLP-1 side effects covers practical ways to manage nausea and other common issues.

5. Track strength, not just the scale

The scale cannot tell you what kind of weight you are losing. Simple markers can help: whether everyday tasks like climbing stairs, carrying groceries, or getting up from a chair feel easier or harder, and whether the weights or repetitions you use in training are holding steady or improving. Some clinicians also use body-composition scans or grip-strength tests to monitor changes over time.

When to talk with your clinician

Reach out if you notice new weakness, fatigue, dizziness, or trouble with balance, or if you are struggling to eat enough. It is also worth discussing a plan for protein, exercise, and monitoring before you start treatment if you are older, postmenopausal, or have a medical condition that affects muscle, kidneys, or activity. If you have questions about how treatment works, our frequently asked questions page is a good place to start.

The bottom line

Some lean mass loss is a normal part of losing weight, with or without medication. GLP-1 studies show that most of the weight lost is fat, but the amount of lean mass lost varies, and people with less muscle to spare have the most to protect. Prioritizing protein, strength training regularly, eating enough, and paying attention to how strong you feel are the most practical steps you can take.

If you are considering weight-loss treatment, Stone Health's clinician-guided weight management program starts with a licensed clinician who reviews your health history and helps you decide whether a treatment may be appropriate for you, including how to support muscle along the way.