GLP-1 Muscle Loss: How to Protect Your Muscle While Losing Weight

Yes, GLP-1 (glucagon-like peptide-1) medications like Ozempic, Wegovy, Mounjaro and Zepbound can cost you muscle. In the big trials, roughly 25% to 40% of the weight people lost was lean mass. You protect it with three things: strength training at least two to three times a week, about 1 gram of protein per pound of lean body mass a day, and moving more between workouts, not less.

I'm Kevin Brown. I've been a physical therapist (PT) for 38 years, I have two artificial hips, and I'm a 3rd-degree black belt in jiu-jitsu. I'm also on a GLP-1 myself.

My doctor put me on it for prediabetes, not weight loss. I take a microdose, about one-tenth of a normal weekly dose. In roughly three years I've lost about 5 pounds. That's it. I wasn't expecting to lose much, and I'm not comfortable losing muscle to get there, because muscle is so important. Not just for looks, but for your metabolic health.

If you're on one of these medications, here's what I want you to know, and what I tell my own patients.

How much muscle do you lose on a GLP-1?

More than most people expect. In the STEP 1 trial of semaglutide (Ozempic and Wegovy), a body-scan substudy found that close to 40% of the weight people lost was lean mass. In the SURMOUNT-1 trial of tirzepatide (Mounjaro and Zepbound), it was about 25%.

One fair caveat: "lean mass" on those scans isn't only muscle. It also includes water and organ tissue. So not every lean pound lost is muscle. But a lot of it is, and that matters.

Here's why it matters even more if you're over 35. You're already losing muscle with age: roughly 3% to 8% per decade starting around 30, and the rate speeds up after 50. By your 70s, studies show people lose close to 1% of their muscle a year, and their strength drops even faster, about 3% a year. Over a decade, that adds up to several pounds of muscle, and that's before a GLP-1 enters the picture. Stack fast weight loss on top of that and you can lose years' worth of muscle in months. Muscle is what gets you up off the floor, carries the groceries and keeps your blood sugar in check. You want to keep it.

Why it happens (it's not just the drug)

Any time you lose weight, some of it comes from muscle. That happens on a diet too. GLP-1s just make you lose weight faster, and they shrink your appetite, so a lot of people end up eating very little protein without noticing.

And here's the part almost nobody talks about. People on GLP-1s tend to move less. A study presented at the Endocrine Society's ENDO 2026 meeting tracked Fitbit data from adults who started a GLP-1. Their daily steps dropped from about 5,047 to 4,487, and their moderate-to-vigorous exercise fell from 28 to 22 minutes a day.

You'd think losing weight would make people more active. Instead, lower energy and less food add up to less movement. Less food plus less movement is the recipe for losing muscle.

You can't control how the drug works. You can control what you do while you're on it.

How to prevent muscle loss on a GLP-1: 3 rules

Rule 1: Strength train, starting this week

This is the big one. Lifting something challenging tells your body, "We need this muscle, don't get rid of it." Cardio is great for your heart, but on its own it doesn't send that signal nearly as well.

In 2025, four major obesity and nutrition organizations put out a joint advisory on GLP-1 care. It recommends strength training at least 3 times a week, plus about 150 minutes of moderate activity like brisk walking. If you've never lifted, start with 2 days a week and work up to 3.

Here's a simple beginner routine. All you need is a chair, a wall or bench, and a resistance band.

Exercise	Sets × reps	What it does
Chair sit-to-stand	2 × 8–12	Legs and hips. The movement you use every time you get up.
Push-ups from a bench or wall	2 × 8–12	Chest, shoulders and arms
Hip bridge	2 × 10–15	Glutes and the back of your legs
Band row	2 × 10–15	Upper back and posture
Bird dog	2 × 6 each side	Core and back stability

Stop each set with 2 or 3 good reps left in the tank. It should feel like work, not like a fight. When the top of the rep range starts feeling easy, make it a little harder. Use a lower chair, a heavier weight or a stronger band. That steady push, the increased stimulus, is what builds and keeps muscle.

Mobility first, strength second. If your hips or knees are stiff, a few minutes of mobility work before you lift will make every exercise feel better.

Rule 2: Eat your protein, and eat it first

Strength training gives your muscles the reason to stay. Protein gives them the building material. On a GLP-1 you need both, because the medication makes it really easy to under-eat.

That same joint advisory suggests 1.2 to 1.6 grams of protein per kilogram of body weight per day while you're losing weight, or about 80 to 120 grams a day. With my clients, I aim for the middle to upper end, and I use one simple rule: about 1 gram of protein per pound of lean body mass.

Lean body mass is everything that isn't fat: muscle, bone, organs and water. Basing protein on lean mass instead of total weight keeps the target realistic if you're carrying a lot of extra weight, because your fat doesn't need protein. Say you weigh 240 pounds and you're 40% body fat. Your lean mass is about 145 pounds, so you'd aim for about 145 grams a day. Going by total weight would have told you to eat 240 grams, which almost nobody on a GLP-1 can do.

Don't know your lean mass? A body composition scan will tell you (more on that below). Until then, start at 100 grams a day and build from there.

If that sounds like a lot when you're barely hungry, here's how I'd make it doable:

Eat the protein first. Before the bread, before the sides. If you fill up halfway through the plate, you got the important part in.
Get some at every meal. Aim for about 25 to 40 grams each time instead of trying to cram it into dinner.
Pick easy, dense foods. Greek yogurt, cottage cheese, eggs, chicken, fish, tuna packets, lean beef, tofu, and a protein shake when you just can't eat.

One caution: if you have kidney disease, talk with your doctor before raising your protein.

Rule 3: Keep moving between workouts

Remember those steps that dropped? Win them back. Walk after meals, take the stairs, park farther away. A short walk after eating is also one of the simplest ways to help your blood sugar, which is exactly why I'm on this medication in the first place. Walking won't build muscle by itself, but it keeps you from sliding into the "less food, less movement" trap.

What about microdosing?

This is my situation, so I get asked a lot. The honest answer: nobody has studied muscle loss in people on microdoses yet. On a low dose, weight usually comes off more slowly, and in my experience as a clinician that gives you more time to build strength alongside it. But a slower pace doesn't make the rules optional. I still train, I still watch my protein, and I still pay attention to my body composition: how much is fat and how much is muscle.

Track your body composition, not just the scale

The scale can't tell you whether you lost fat or muscle. Two people can lose the same 10 pounds and end up in completely different places.

That's why I just got an InBody unit. It's a bioimpedance (BIA) scanner: it sends a tiny, harmless electrical signal through your body to estimate how much of you is muscle, fat and water. It isn't perfect. Hydration, a recent meal or a hard workout can shift the numbers. But scanned the same way each time (same time of day, before eating), it's very good at showing which way you're trending. It also gives you your lean body mass, which is the number I use to set your protein target.

I'm using it to run a body composition challenge: gain muscle, lose fat, or both. If you're local to Encinitas and want in, email me.

Frequently asked questions

Does Ozempic cause muscle loss if you work out?

You can still lose some lean mass, because any time you lose weight some of it comes from muscle. But strength training at least two to three times a week, plus enough protein, is the best-supported way to keep that loss small. Working out is what tells your body the muscle is worth keeping.

How much protein should I eat on a GLP-1?

A 2025 joint advisory from four obesity and nutrition societies suggests 1.2 to 1.6 grams per kilogram of body weight per day during active weight loss, or about 80 to 120 grams per day. I aim for the middle to upper end with a simple rule: about 1 gram per pound of lean body mass, which keeps the target realistic if you have a lot of weight to lose. Spread it across your meals and eat the protein first, since GLP-1s shrink your appetite. If you have kidney disease, check with your doctor first.

Can you build muscle on a GLP-1?

Yes, especially if you are new to strength training. Beginners respond quickly to a real training stimulus. Building muscle while eating less is harder than holding on to it, so the realistic first goal is to keep what you have and lose mostly fat.

Does microdosing a GLP-1 cause muscle loss?

No study has measured muscle loss in people on microdoses yet. Weight usually comes off more slowly on a low dose, but the same rules apply: strength train, eat enough protein and keep moving.

Should I stop or lower my dose to protect my muscle?

Don't change your medication on your own. That's a conversation for your prescriber. What you can change today is how you train and eat.

The bottom line

A GLP-1 can be a great tool. But losing weight isn't the win if half of what you lose is the muscle you need to stay strong, steady and independent. Lift something two or three times a week, eat your protein first, keep walking, and judge your progress by what you're made of, not just what you weigh.

You're not getting too old. You just need to train and exercise wisely.

This article is for general education and isn't medical advice. Don't change your medication without talking to your prescriber. If you have pain, a recent injury or surgery, kidney disease or another medical condition, check with your doctor or physical therapist before starting a new exercise or nutrition plan.

Sources

Mozaffarian D, et al. Nutritional Priorities to Support GLP-1 Therapy for Obesity: A Joint Advisory from the American College of Lifestyle Medicine, American Society for Nutrition, Obesity Medicine Association and The Obesity Society. 2025.
Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). New England Journal of Medicine, 2021, including its body-composition (DXA) substudy.
Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). New England Journal of Medicine, 2022, including its body-composition substudy.
Endocrine Society. Exercise decreases among people taking GLP-1 medication. Presented at ENDO 2026; conference findings, not yet peer-reviewed.
Mitchell WK, et al. Sarcopenia, Dynapenia, and the Impact of Advancing Age on Human Skeletal Muscle Size and Strength; a Quantitative Review. Frontiers in Physiology, 2012.