GLP-1 / Weight-loss medications
GLP-1 Muscle-Loss Calculator
On GLP-1 medications, roughly 25 to 39 percent of the weight you lose is lean mass, not fat (Prado et al., 2024). So a 15 kg loss can strip about 4 to 6 kg of muscle. This calculator estimates your likely muscle loss; resistance training and enough protein are what protect it.
On a GLP-1 like Ozempic, Wegovy or Mounjaro, not all of the weight you lose is fat. A large share can be muscle. Enter your numbers to estimate how much muscle is at risk, then see how to keep it.
Why so much GLP-1 weight loss is muscle
GLP-1 medications work by cutting appetite, which puts you in a large calorie deficit. The scale moves fast, but a deficit does not choose fat for you. Across trials of these drugs, roughly 25 to 39% of the total weight lost came from lean, fat-free mass rather than fat (Prado et al. 2024). That muscle is the tissue that keeps you strong, holds your metabolic rate up, and protects the weight loss from coming back. Losing it quietly is the cost most people are not told about.
The muscle is the part you protect
You cannot make muscle loss zero, but you can change the ratio sharply. In a randomised trial of dieting adults, those who added resistance training kept more lean mass than those who only did aerobic work (Villareal et al. 2017). Two things do the work: strength training tells your body to keep the muscle, and enough protein gives it the raw material. That is the entire job while the medication handles the fat. The GLP-1 Muscle Protocol is the 12-week strength-and-protein plan our coaches use for exactly this, written and medically reviewed by a doctor, with a complimentary sample chapter you can read first.
GLP-1 muscle loss, by the numbers
| Total weight lost | Likely muscle (25 to 39%) |
|---|---|
| 10 kg | about 2.5 to 3.9 kg |
| 15 kg | about 3.8 to 5.9 kg |
| 20 kg | about 5.0 to 7.8 kg |
Source: Prado et al. 2024, Lancet Diabetes Endocrinol. A range, not a precise figure: tirzepatide tends toward the lower end, and training plus protein moves you lower still.
GLP-1 muscle loss, common questions
- How much muscle do you lose on Ozempic or a GLP-1?
- In trials of GLP-1 medications, roughly 25 to 39% of the total weight lost came from lean (fat-free) mass rather than fat (Prado et al. 2024). So for every 10 kg lost, around 2.5 to 3.9 kg can be muscle. The exact share depends on your training, your protein intake, and the specific medication, and it is the part you can protect.
- Does tirzepatide (Mounjaro, Zepbound) cause less muscle loss than semaglutide?
- Tirzepatide trials tend to show a more favourable ratio, with a larger share of the loss coming from fat. The 25 to 39% band still applies to the drug class, so the calculator uses it for all GLP-1s and you should still train and eat protein to keep the muscle. The medication handles the fat; the muscle is on you.
- Can you avoid losing muscle on a GLP-1?
- You cannot make it zero, but you can change the ratio sharply. In a randomised trial of dieting adults, those who added resistance training preserved more lean mass than those doing aerobic work alone (Villareal et al. 2017). Resistance training is the signal that tells your body to keep the muscle; adequate protein is the raw material it keeps it with.
- Is this calculator a medical assessment?
- No. It is an estimate built from population trial averages, not a measurement of your body, and it is not medical advice. For an actual reading of your muscle and fat, use a DEXA or InBody scan, and keep your medication decisions with your doctor.
More complimentary Healthspan calculators
Cardiorespiratory
VO2 Max Calculator →
Strength
Grip Strength Test →
Body Composition
Waist-to-Height Ratio →
Stability
Sitting-Rising Test →
Overall
Fitness Age Calculator →
Running
Running Pace Calculator →
Running
Heart Rate Zones Calculator →
Body Composition
Fat Loss Calculator →
Nutrition
Protein Intake Calculator →
Body Composition
Body Fat Percentage Calculator →
All calculators + the Healthspan Audit →