Will I Lose Muscle Instead of Fat on GLP-1 Medications Like Ozempic?

You’ve probably seen something like this floating around the internet: “Up to 40% of total weight lost on GLP-1s was lean mass.”

It’s not wrong, but without an explanation, it sounds like you’re just losing muscle left and right, and that’s not really the whole picture.

That 40% stat came from a 2024 systematic review¹ that looked at multiple semaglutide studies to see how people were actually losing weight (not just how much, but what kind). They pulled data from six different trials with over 1,500 adults who were overweight or living with obesity, using body scans to figure out how much was fat, muscle, and everything in between.

But when people see that number out of context, it usually causes major panic (rightfully so) and a bunch of back-and-forth, mostly because most people don’t realize “lean mass” isn’t just skeletal muscle.  

So, let’s clear up what’s going on behind that number and what you can do to protect your muscle while taking a GLP-1.

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What Makes Up Lean Body Mass?

Lean body mass includes everything in your body that isn’t fat, like:

• Muscles
• Bones
• Organs
• Tendons
• Ligaments
• Connective tissue
• Water

An article in Diabetes, Obesity, and Metabolism² explains that a big chunk of the lean mass lost with GLP-1 medications isn’t actually muscle; it’s coming from other parts of the body.

But we still can’t get too hung up on the numbers because one study might say lean mass loss is 40%, and another says it’s only 15% (they’re not all measuring the same way, and they’re definitely not just looking at muscle).

Some of that “loss” could be water weight, smaller organs (which naturally shrink when you’re eating less), or even fat that was stored inside your muscles, proving that not all of that lean body mass loss comes from your biceps or glutes.

That same article also shows that in most cases, muscle quality actually improves during GLP-1 weight loss. So, you might lose a little size, but what’s left is high-quality muscle that actually works better, is leaner, stronger, and more efficient (especially if you work to maintain and build it up).

Of The Three Types, Only One Kind of Muscle Builds Your Strength

When people talk about lean muscle, they usually mean the kind you build at the gym, but your body actually has three types of muscle, and they all matter.

• Cardiac muscle makes your heart beat and pushes blood through your body 24/7.
• Smooth muscle wraps around your organs and keeps things moving, like digestion, breathing, and other behind-the-scenes work you don’t consciously control.
• Skeletal muscle, the kind you can see and strengthen, the stuff that helps you lift, squat, carry groceries, stand tall, and even smile.

All three are made from protein, but skeletal muscle is the only one you can train and grow on purpose. And if you’re on GLP-1s, keeping skeletal muscle on your body is non-negotiable because when you lose weight fast (via medications, diet, or exercise), your body pulls from fat stores and lean body mass (LBM), which includes muscle, unless you give it a reason not to.

How Much Skeletal Muscle is Included in Lean Body Mass?

It varies, but skeletal muscle usually makes up about 35-45% of LBM³, depending on things like gender, age, activity level, and hormone balance.

LBM typically accounts for 69-75% of total body weight in healthy, non-athlete adult women, while fat mass makes up the remaining 25- 31%.

So, let’s say a woman weighs 140 lbs.:

• Of her total body weight, 42 lbs. (30%) is body fat,
• 98 lbs. (70%) is lean mass,
  • 34-44 lbs of that lean mass is skeletal muscle, and the rest is made up of water, bone, organs, and other tissues.

So, if she loses 15 lbs. of lean mass, it’s likely only 5-7 lbs. of that was actual muscle, and maybe even less if she’s strength training and eating well.

What’s Actually Happening When You Lose Weight?

When you’re in a calorie deficit (meaning you’re using more energy than you’re eating), your body starts pulling from its own energy reserves to keep things running.

And while the goal is usually fat loss, your body doesn’t just burn fat like it’s picking from a menu.

Without enough protein, strength training, or fuel from carbs, it can also break down muscle tissue and other parts of your lean mass, especially during rapid weight loss, like what happens on GLP-1s.

Water weight drops, too, especially early on. That’s not fat loss or detox magic, it’s your body burning through stored glycogen (your muscles’ carb stash), which also holds onto water. When glycogen goes down, water goes with it. So, if the scale moves fast at first, that’s normal… but it’s not all fat.

Muscle Is Expensive for the Body to Keep

Muscle is metabolically active, meaning it burns more calories even when you’re just sitting around. That’s amazing for your long-term metabolism and strength… but your body doesn’t always see it that way during rapid weight loss.

Instead, your body starts asking: “What can I get rid of that costs me energy to maintain?”

And if you’re not eating enough protein or using your muscles, your body may decide you don’t need them and start breaking them down.

Some muscle loss is expected when you lose weight. But too much, too fast means you’re not just getting smaller, you’re getting weaker. And that can lead to some real issues:

• Slower Resting Metabolic Rate – Less muscle means your body burns fewer calories at rest. That makes it harder to keep weight off long-term, especially after stopping the meds, and leads to what people often call a “slower” metabolism.
• Poor balance and joint support – Muscle keeps you stable and protects your joints. Without it, stairs, bending, or even walking can feel harder.
• More fatigue – Less muscle means your body has to work harder to do everyday stuff, so you tire out more quickly.
• Higher risk of injury or falls – Weak muscles can’t protect you when you trip, twist, or carry awkward loads. Your knees, hips, and back take the hit.

Okay, So… How Do You Know If You’re Losing Muscle?

Here are some signs your body might be shedding more muscle than it should, especially if you’re on a GLP-1:

• You feel wiped out doing basic stuff like carrying groceries or walking up stairs
  • Why: Muscle gives you stamina and strength. Lose too much, and everyday stuff starts to feel like a workout.

• You’re slouching more, or your body feels “wobbly”
  • Why: Muscles keep your joints stable and your spine upright. If they’re breaking down, everything feels less sturdy.

• You’re shrinking but still feel squishy; often called the “skinny fat” effect.
  • Why: You’ve lost weight, but without muscle underneath, there’s no shape or tone, just a smaller version of the same.

• You’re losing weight without strength training (huge red flag)
  • Why: When your body needs energy, it’s pulling from the muscle you’re not using.

• You’re not eating enough protein
  • Why: Your body might start breaking down muscle to get what it needs. Protein is not optional during weight loss; it’s fuel and protection for lean tissue.

• You’re strength training and lifting weights, but not progressing (or getting weaker)
  • Why: Your performance is dropping because you’re losing more muscle than you’re building. Losing weight should not mean losing strength. If it does, something’s off.

• You’re sick all the time or healing slower than usual
  • Why: Muscle plays a role in recovery and immune function. So, if your body is always rundown, it might struggle to keep up without the muscle it needs to repair and defend itself.

How to Keep (and Build) Muscle While on GLP-1s

GLP-1 medications help reduce appetite, so you’re probably eating less, therefore moving less, and maybe not getting enough of what your muscles need to stay strong.

Here’s how to protect your strength and support muscle while losing weight:

• Strength Train 2–3 Times a Week: You don’t need to crush it daily, but your muscles need a reason to stick around. Prioritize full-body strength training or split routines that challenge you, not exhaust you. Think: steady progress, not punishment.

• Slow Down Your Reps: Fast and sloppy doesn’t build strong, toned muscle. Slow, controlled movements (especially during the lowering phase) help your muscles work harder without needing to lift super heavy. Plus, it’s gentler on joints and reduces injury risk.

• Rest Is Part of the Process: When your energy dips (whether from the meds or the calorie deficit), your body needs recovery. That means:
  • Taking rest days seriously
  • Giving your muscles time between workouts
  • Not panicking if you initially need more time to bounce back

• Eat Enough Protein (Even If You’re Not Hungry): Protein, made up of long chains of amino acids, is what your muscles are built from. If you’re not getting enough through food, your body will start breaking down muscle tissue to get the amino acids it needs. To keep it simple, aim for at least 1 gram of protein per pound of your ideal body weight, spread out over the day.

• Don’t Ignore Fiber: GLP-1s can slow digestion, so getting enough fiber helps keep things moving. Women generally need around 25g/day, but to avoid GI issues, don’t go from zero to 25 overnight; build up slowly with foods like berries, beans, oats, or a supplement if needed.

• Hydrate Like You Mean It: Water helps with nausea, digestion, energy, recovery, muscle function, and even skin health. If your appetite’s low, hydration can slip, too, so stay on top of it. Sip throughout the day, not just at meals.

Safe Exercise Progressions After GLP-1 Weight Loss

If you’re new to movement or just getting back into it after a long break, I strongly recommend working with a professional, especially if you’re unsure where to start or struggle with proper form. But if that’s not an option right now, here’s a smarter approach than randomly following fitness trends online:

• Start with the Basics
  • Forget the flashy stuff on social media. Rebuild your foundation first: posture, balance, breathing, and how your body moves through space. If it feels “too easy” (right now), that usually means you’re doing it right.

• Begin with Bodyweight, Then Build
  • Start where your body is now. Master bodyweight movements first, then gradually add resistance bands or light dumbbells. You don’t need to “go heavy” right away; just stay consistent and pay attention to how your body moves.

• Rebuild Core & Stability
  • Your core isn’t just your abs; it’s your pelvic floor, hips, and glutes, too. These muscles are the foundation for everything else.

• Protect Your Joints
  • Rapid weight loss can throw your joint stability off, especially around the ankles, knees, hips, and shoulders. Go slow, check your form often, and don’t ignore little aches; they’re usually early warning signs. Listen to your body.

• Adjust Weekly, Not Randomly:
  • Check in with yourself every 1–2 weeks. How’s your energy? How’s your recovery? Can you do more well, not just more? Don’t rush progress, but make sure to track it.

• Move More:
  • Movement is movement, and when it’s done consistently, it adds up. Even if you start with a 10–15-minute walk daily and build from there, that still counts.

• Increase your NEAT (Non-Exercise Activity Thermogenesis):
  • Walk, clean, take the stairs, or do yard work. It’s not formal exercise, but it still burns energy, supports your metabolism, and helps you feel better overall, especially during weight loss.

Free Download:

This isn’t a full program, but it’s a great place to start if you’re not sure what your body needs right now. It’s structured for women on GLP-1s who want to train with purpose, without jumping into something random or too intense too soon. The focus here is on quality reps, solid movement patterns, and waking up your strength system the right way, especially if it’s been a while.

Final Thought

GLP-1s reduce appetite and lower calorie intake, which can lead to muscle loss, but not because of the medication itself. It’s the calorie deficit that puts muscle at risk, just like with any form of weight loss.

The difference comes down to what you do with your body while the scale is moving. GLP-1s don’t change patterns, habits, or the rules of muscle retention. Exercise still matters. Protein still matters. And your body will adapt and respond to what you consistently give it.

Maintaining or building muscle isn’t about getting bulky or living in a gym. It’s about protecting your strength, energy, and ability to move well long-term, because if you can’t move well, keep up with your life, or enjoy the energy you thought weight loss would give you, then something’s missing.

If you’re looking for a plan that actually makes sense for your body, I build personalized strength programs for women using GLP-1s who want to protect muscle, improve energy, and feel strong in a body that’s changing fast.

You can learn more about my program, The Remedy, or click here to get to know me.

Whenever you are ready to try something that’s built around you, I’d love to help. Feel free to reach out with any questions!

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Resources

1. NIH PubMed, A systematic review of the effect of semaglutide on lean mass: insights from clinical trials, Bikou A, Dermiki-Gkana F, Penteris M, Constantinides TK, Kontogiorgis C. A systematic review of the effect of semaglutide on lean mass: insights from clinical trials. Expert Opin Pharmacother. 2024 Apr;25(5):611-619. doi: 10.1080/14656566.2024.2343092. Epub 2024 Apr 18. PMID: 38629387. https://pubmed.ncbi.nlm.nih.gov/38629387/ ↩︎
2. NIH PubMed, Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies, Neeland IJ, Linge J, Birkenfeld AL. Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies. Diabetes Obes Metab. 2024 Sep;26 Suppl 4:16-27. doi: 10.1111/dom.15728. Epub 2024 Jun 27. PMID: 38937282. https://pubmed.ncbi.nlm.nih.gov/38937282/ ↩︎
3. American Physiology Society, Journal of Applied Physiology, Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr https://journals.physiology.org/doi/full/10.1152/jappl.2000.89.1.81?utm_source ↩︎

Photo Credits

Fit Female in Activewear Holding Dumbbells by Andrea Piacquadio from Pexels

Person Showing Weight Loss with Loose Pants by NOMADNES