Ozempic, Wegovy, Mounjaro: How to Avoid Muscle Loss and Track Your Progress

GLP-1 medications such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, sold as Zepbound for weight management in the US) produce large weight losses, often faster than diet alone. Which raises the question everyone asks sooner or later: am I losing fat, or muscle too? The answer from the research is "both". The good news is that you have real levers to limit muscle loss, and simple ways to check that the weight you're losing is the right kind.

This article is for information only. These are prescription medications: never start, change or stop a treatment without your doctor's advice.

In short

• On a GLP-1, part of the weight you lose is lean mass: about a quarter in the SURMOUNT-1 trial (tirzepatide), a share similar to a conventional diet.
• Strength training (two to three sessions a week) and enough protein are the two recommended ways to protect your muscle.
• The scale doesn't tell you what you're losing: also track your waist, body fat percentage, training loads and monthly photos.
• Weight regain after stopping is common: keeping an eye on your numbers helps you spot it early.

How much weight do Ozempic, Wegovy and Mounjaro help you lose?

The two landmark trials in adults with obesity or overweight, without diabetes, give clear orders of magnitude.

These are averages: some people lose much more, others much less. They were also achieved alongside diet and physical activity counseling. Ozempic contains the same active ingredient as Wegovy, but it is approved for type 2 diabetes, at different doses.

Do you lose muscle on a GLP-1?

Yes, partly. Any substantial weight loss, whatever the method, lowers both fat mass and lean mass, and GLP-1 drugs are no exception. Two substudies measured body composition with DXA, the reference method in research:

• STEP 1, semaglutide (Wilding et al., Journal of the Endocrine Society, 2021, 140 participants): over 68 weeks, total fat mass fell by 19.3%, visceral fat by 27.4% and lean mass by 9.7%. Because fat went down faster, the proportion of lean mass in the body actually rose by about 3 percentage points.
• SURMOUNT-1, tirzepatide (Look et al., Diabetes, Obesity and Metabolism, 2025, 160 participants): over 72 weeks, fat mass fell by 33.9% and lean mass by 10.9%. About 75% of the weight lost was fat and 25% lean mass, a split close to the one seen with placebo.

Two important caveats. First, "lean mass" doesn't mean "muscle": it includes water and organs, and DXA even counts some of the fat stored in the liver and muscles as lean tissue. Second, losing some lean mass is expected when you carry less weight around every day. The real goal is to limit the loss of functional muscle, the kind that keeps you strong and independent, especially after 50.

How to prevent muscle loss on Ozempic, Wegovy or Mounjaro

In 2025, four US societies (the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society) published nutrition priorities to support these treatments (Mozaffarian et al., American Journal of Clinical Nutrition). Preserving muscle rests on two pillars.

1. Strength training is non-negotiable

Muscle needs a reason to stay, and that reason is working against resistance. Aim for two to three full-body sessions a week (squats or sit-to-stands, pushes, pulls, hinges) with progressive overload: a little more weight or a few more reps as the weeks go by. Walking and cardio remain great for your health, but they don't replace resistance work. If you're a beginner or have a health condition, get guidance from a coach or physical therapist.

2. Enough protein, despite a smaller appetite

This is the main challenge on a GLP-1: you eat much less, and protein drops along with everything else. The ranges usually cited during weight loss are roughly 1.2 to 1.6 g of protein per kilogram of body weight per day (about 0.55 to 0.75 g per pound). A few tips:

• start each meal with your protein source (eggs, fish, meat, tofu, legumes, dairy);
• spread it over three or four meals or snacks rather than one big meal you'll struggle to finish;
• lean on protein-dense, low-volume foods (Greek yogurt, cottage cheese, eggs) when your appetite is at its lowest.

If you have kidney disease or any doubt, ask your doctor or a registered dietitian to set your target.

3. Don't chase speed at all costs

Skipping meals because you're not hungry, or celebrating a very fast drop on the scale, isn't necessarily good news for your muscles. Sleep and hydration matter too, especially to limit the fatigue and digestive side effects that are common early in treatment.

How do you know if you're losing fat or muscle?

The scale weighs everything at once: fat, muscle, water, the contents of your gut. On a GLP-1 it often drops fast, which makes it all the more useful to cross-check several indicators. To understand why the number alone is misleading, see our guide on losing inches but not weight.

The most reassuring signal: body fat percentage and waist going down while your training loads hold steady or go up. On the other hand, if you're losing weight fast but your loads are dropping, you feel weak or climbing stairs is getting harder, talk to your doctor.

For body fat, consistency matters more than precision: a bioimpedance scale used every morning on an empty stomach gives you a usable trend, even if the absolute number is approximate. Our comparison of ways to measure your body fat covers the methods, and our guide on how to take body measurements shows where to place the tape.

Why progress photos help on a GLP-1

When you lose 10 or 15% of your body weight in a few months, your brain struggles to keep up: many people say they don't recognize themselves, or that they can't see any change at all. Photos taken every month, in the same pose and the same light, let you judge your shape objectively, and spot whether your arms or legs are "shrinking" faster than your waist. Our guide on how to take progress photos walks you through the method.

In Marava, the ghost overlay shows your previous photo as a transparent layer so you can match the exact same pose, and the timeline lets you scroll through the months. On the dashboard, your weight, body fat percentage and BMI appear with their trend lines next to your photos. And because these images are personal, they're blurred by default when you open the app and encrypted on our servers.

What happens when you stop?

In the STEP 1 trial extension (Wilding et al., Diabetes, Obesity and Metabolism, 2022), participants regained on average about two-thirds of the weight they had lost within a year of stopping semaglutide, and most cardiometabolic improvements faded. The authors see this as a sign that obesity is a chronic disease that often requires long-term treatment.

Whether you continue or stop with your doctor, two things help: having kept as much muscle as possible, and continuing to track your numbers. Regain spotted at 2 kg (4–5 lb) is far easier to manage than regain discovered at 10 kg (22 lb). If the scale gets stuck along the way, our article on the weight loss plateau will help you sort things out.

Conclusion

Ozempic, Wegovy and Mounjaro make you lose fat, but also some lean mass, about a quarter of the weight lost in the trials. Regular strength training and enough protein are your best tools to protect your muscle. And since the scale can't tell fat from muscle, also track your waist, body fat percentage, strength and monthly photos: that combination tells you whether you're losing the right kind of weight.

To go further on losing fat while keeping, or even building, muscle, read our guide to body recomposition.