How much of your Ozempic or GLP-1 weight loss is muscle?
In the trials that scanned people on semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound), 25–39% of the weight lost was lean mass.
GLP-1 and Ozempic muscle loss calculator
Question 1 of 5Which medication are you on?
Each one was tested in its own trial, with different results.
Your weights and results stay on this page.
What did you weigh when you started?
Your best guess is fine.
And what do you weigh now?
34 lb lost so far, 15% of where you started
Are you lifting weights at least twice a week?
Strength training is the main thing that protects muscle while you lose weight.
Have you had a body composition scan?
A DEXA, InBody or similar. It decides what we suggest next.
You've lost
34 lb 15% of your starting weight
Your weight today is the same as when you started, so there's no loss to split yet.
Trials suggest 9–13 lb of that may be lean mass, muscle included.
In the STEP 1 trial's scan sub-study, about 39% of the weight lost on semaglutide was lean mass. For you, that would be 13 lb.
Worth knowing: strength training two or three times a week, and enough protein, are the main ways to hold on to muscle while you lose weight. Ask your prescriber what protein target fits you.
Good: strength training and enough protein are the main ways to hold on to muscle while you lose weight. The trials didn't require either, so your share may well be lower. A scan shows whether it is.
Your next step
Get a baseline scan
A scan now shows where you stand, and the next one shows whether you keep your muscle from here.
- Scan 1 · this monthYour baseline: fat, lean mass and bone
- Scan 2 · in 12 weeksWhat the next weight you lose is made of
Scan again now
You already have a “before”. A scan now shows how much of what you've lost was fat and how much was muscle.
- Scan · this monthCompare it with your first one
- Then every 12 weeksWhile you're still losing
Time for a follow-up
Eight to 12 weeks after your last scan is when a change shows clearly. Book it for the same time of day, before eating.
- Scan · 8–12 weeks after your lastThe same clinic, if you can
- Then every 12 weeksWhile you're still losing
A DEXA scan splits your weight into fat, lean mass and bone, arm by arm and leg by leg, in about 10 minutes. No referral needed when you pay cash.
Updated October 8, 2026 · Based on the STEP 1 and SURMOUNT-1 trials · Editorial standards
Why the muscle part matters
- Strength as you age. Losing muscle raises the risk of weakness, frailty and falls later in life.
- Blood sugar. Muscle is where most of the sugar from a meal ends up. Less of it can work against the reason many people start a GLP-1.
- What the scale hides. Two people who each lose 30 lb can end up in very different shape. Only a body composition measurement tells them apart.
What the trials found
Two large trials measured body composition with DEXA in a sub-group of participants. In STEP 1 (opens in a new tab) (semaglutide, sold as Ozempic and Wegovy), lean mass was about 39% of the weight lost. In SURMOUNT-1 (opens in a new tab) (tirzepatide, sold as Mounjaro and Zepbound), it was about 25%.
An example: someone who goes from 230 lb to 196 lb on semaglutide has lost 34 lb. At the STEP 1 average, about 13 lb of that would be lean mass; across the two trials, 9–13 lb.
Those are averages across many people. Lean mass also includes organs, water and other non-fat tissue, so not all of it is muscle. Your own share depends on how fast you lose, what you eat and whether you train, which is why the only way to know it is to measure it.
How to keep track
A DEXA body composition scan takes about 10 minutes and splits your weight into fat, lean mass and bone, arm by arm and leg by leg. Scan once now for a baseline, then again 8 to 12 weeks later: the difference shows what the weight you lost in between was made of.
See DEXA prices near you, or start with a free estimate from the body fat calculator.
GLP-1 muscle loss: FAQ
Do you lose muscle on Ozempic or Wegovy?
Some, alongside fat. In the STEP 1 trial, about 39% of the weight lost on semaglutide was lean mass, measured by DEXA in a sub-study. Lean mass includes muscle but also organs, water and other non-fat tissue, so not all of it is muscle.
Do you lose muscle on Mounjaro or Zepbound?
In the SURMOUNT-1 trial's DEXA sub-study, about 25% of the weight lost on tirzepatide was lean mass and the rest was fat.
How can I keep muscle on a GLP-1?
Strength training and eating enough protein are the approaches most often recommended to hold on to muscle while losing weight. Ask your prescriber or a dietitian what targets fit you.
How do I know how much muscle I've lost?
A DEXA body composition scan splits your weight into fat, lean mass and bone, region by region. One scan now and another 8 to 12 weeks later shows what the weight you lose in between is made of.
Medical Disclaimer: The information provided on this website is for general informational purposes only and is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. DEXA scan results should be interpreted by a qualified healthcare professional.