GLP-1 drugs and muscle loss: why it matters
GLP-1 weight-loss drugs such as semaglutide and tirzepatide curb appetite and can bring weight down substantially. But when you lose weight, you lose more than fat: lean mass (everything except fat), including muscle, goes down too. This happens with any weight loss from eating less, not just with these drugs, but the faster and larger the weight loss, the more muscle you may lose.
That may not be a big problem for younger people, but older adults are different. Muscle shrinks naturally with age even without dieting, and when weight-loss muscle loss is added on top, everyday abilities such as walking, climbing stairs, and getting up from a chair can decline and the risk of falls can rise. That is why experts stress that people 65 and older using these drugs should pay special attention to protecting their muscle.
How much lean mass was lost in clinical trials?
Here are the main trials that measured body composition precisely. The two studies differed in participants and duration, so the drugs cannot be compared directly.
| Trial | Duration | Weight loss | Share of weight lost that was lean mass |
|---|---|---|---|
| STEP 1 (semaglutide; NEJM, published 2021) | 68 weeks | about 15% | about 40% |
| SURMOUNT-1 (tirzepatide; body composition analysis published 2025) | 72 weeks | about 21% | about 25% |
For example, if someone lost 10 kg (22 lb), about 2.5–4 kg (5.5–9 lb) of it was lean mass. Lean mass includes water and organs as well as muscle, so not all of it is muscle, but it is clear that muscle mass can drop meaningfully.
Can exercise protect your muscle?
In a 2025 joint advisory, the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society made adequate protein intake and strength training to preserve lean mass a key recommendation during GLP-1 treatment. A trial in Denmark (NEJM, 2021) also found the greatest fat loss in the group that combined a GLP-1 drug with exercise.
There are still few studies that directly test strength training in older adults taking GLP-1 drugs. Even so, it has long been established that strength training is the most reliable way to maintain muscle mass and strength at any age, so it is recommended alongside these drugs.
How to exercise to prevent muscle loss
| Strength training | 2–3 days a week, using all the large muscles: legs, buttocks, back, chest, shoulders, and arms |
|---|---|
| Repetitions | 8–12 per exercise × 1–3 sets; the last 2–3 should feel hard |
| Aerobic | 150 minutes a week of brisk walking or similar (alongside strength training) |
| Balance | 3+ days a week (especially important when weight drops quickly) |
1. Lower-body strength first
The thigh and buttock muscles you use to walk and stand are the largest in your body, and the quickest to shrink with age. Make chair squats your foundation, and add heel raises and side leg lifts while holding a chair.
2. Add upper-body strength
Seated rows, biceps curls, and chest-level pull-aparts with a resistance band work the back, arms, and shoulders evenly. Wall push-ups, with your hands against a wall, are another good upper-body exercise.
3. Increase the challenge gradually
Muscle is maintained and grows only when it gets a "somewhat hard" challenge. Once you can do 2–3 sets of 12 with good form, move up one band strength or slow down the lowering phase to raise the intensity.
4. Keep walking and doing balance exercises
Rapid weight loss can change your sense of balance. Maintain your fitness with walking, and build a body that doesn't fall easily with balance exercises.
What to eat alongside exercise
On GLP-1 drugs, you eat less overall, so protein easily falls short. To protect muscle, protein matters as much as exercise.
- Protein first at every meal: When your appetite is low, eat protein foods such as fish, eggs, tofu, lean meat, or milk before rice, bread, or other starches.
- Spread it out: If large portions are hard, spread protein evenly over three meals and add snacks such as milk or yogurt.
- Amounts for reference: The Dietary Reference Intakes for Koreans (2020) recommend 60 g of protein a day for men and 50 g for women aged 65 and older. The European Society for Clinical Nutrition and Metabolism (ESPEN) and the PROT-AGE study group suggest 1.0–1.2 g per kg of body weight a day for healthy older adults, or 60–72 g a day at 60 kg. One egg has about 6 g of protein, and half a block of Korean tofu (150 g) about 12–14 g.
- Kidney disease? Ask first: Some people with reduced kidney function should not increase protein, so always agree on an amount with your doctor.
Precautions for exercising during GLP-1 treatment
Please keep these in mind
- Watch for low blood sugar: If you also take insulin or a sulfonylurea diabetes drug, your blood sugar can drop during exercise. Carry candy or juice, and stop at once if you get cold sweats, shakiness, or dizziness.
- Avoid exercising on an empty stomach: With much smaller meals, exercising hungry can make you dizzy. Eat at least a little, then exercise 1–2 hours later.
- Stay hydrated: Side effects such as nausea, vomiting, or diarrhea make dehydration more likely. Drink plenty of water before and after exercise.
- Rest on bad days: On days when nausea is severe, such as right after starting the drug or increasing the dose, lower the intensity or take a break.
- Discuss the medication with your doctor: This article covers exercise. Always talk to your prescribing doctor about starting, stopping, or changing the dose of the drug.
Please keep in mind
- This article is based on information checked as of the date shown at the top. New research or changes in official guidelines may change the details, so please use it as a reference rather than taking it as definitive.
- For an accurate diagnosis and advice about your health, please see a doctor in person.