On Ozempic or Mounjaro? Here's How to Protect Your Muscle While You Lose Weight

GLP-1 medications like semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) have been genuinely transformative for weight loss. Patients are seeing results they couldn't achieve with diet and exercise alone — and for many, these medications have been life-changing.

But there's an important side effect that doesn't get enough attention: muscle loss. And as your family physicians, it's something we talk about with every patient we put on a GLP-1 medication.

The muscle loss problem with GLP-1s

When you lose weight — through any method — some of that weight comes from fat, and some comes from muscle (lean mass). This is normal. The concern with GLP-1 medications is the proportion of weight lost that comes from muscle.

Studies show that between 26–40% of total weight lost on semaglutide or tirzepatide can come from lean mass, including muscle. In the large STEP-1 semaglutide trial, lean mass decreased by about 9.7% while fat mass fell by 19.3%. That ratio isn't ideal — and for certain patients, it's a meaningful concern.

Why does muscle loss matter? Muscle is your metabolic engine. It controls blood sugar after meals, supports bone health, drives your resting metabolism, and is the foundation of strength and function as you age. Losing too much muscle while on a GLP-1 medication can reduce the metabolic benefits of weight loss — and increase your risk of frailty and insulin resistance over time.

Research presented at the Endocrine Society's 2025 annual meeting found that women and older adults are at the highest risk for muscle loss on semaglutide — two groups who are also among the most common users of these medications.

The good news: you can protect your muscle

This is not a reason to avoid GLP-1 medications. It is a reason to use them correctly — under the guidance of a physician who monitors your body composition and gives you a plan to protect your muscle while you lose fat. Here's what the evidence supports:

Strategy 1 — Eat enough protein. Aim for 100g per day

Protein is the building block of muscle. When you're in a calorie deficit — which is exactly what GLP-1 medications create — your body needs adequate protein to maintain muscle mass. Without it, muscle breakdown accelerates.

Current research supports aiming for a minimum of approximately 100 grams of protein per day while on a GLP-1 medication. This is higher than the standard dietary reference intake of 0.8 g/kg, and for good reason — the standard intake was designed for sedentary adults maintaining their weight, not for people losing weight rapidly on medication.

Practical protein targets: Spread your protein intake across 3–4 meals. Aim for at least 30–35 grams of protein per meal. Good sources include eggs, Greek yogurt, cottage cheese, chicken, fish, lean beef, tofu, legumes, and protein shakes when needed. GLP-1 medications often reduce appetite — make sure the food you do eat is protein-rich rather than filling up on lower-quality calories.

Strategy 2 — Resistance train at least 2–3 times per week

Resistance training is the most powerful tool we have for preserving muscle during weight loss. Multiple systematic reviews confirm that strength training effectively counteracts the lean mass loss associated with GLP-1 medications and caloric restriction.

In a 6-month study of 200 adults taking semaglutide or tirzepatide who received guidance on resistance training and protein intake, participants lost an average of 13% of their body weight but only about 3% of their muscle mass — a dramatically better ratio than seen in medication trials alone.

You don't need to lift heavy. Resistance exercise with lighter weights and higher repetitions (20–25 reps) is just as effective for preserving muscle as heavier lifting — and significantly safer, especially for patients who are new to strength training.

Good options include:

• Free weights or machines at a gym

• Resistance bands (inexpensive and effective at home)

• Bodyweight exercises: squats, lunges, push-ups, rows

• Classes like Pilates, barre, or circuit training

Strategy 3 — Stay active throughout the day

Beyond structured exercise, daily movement matters. Walking 8,000 steps per day is a good target for general activity. Every step you take is your body using its muscles — and keeping them engaged.

What we do differently at Plasencia Family Medicine

At our practice, we don't just prescribe a GLP-1 medication and send you home. We use body composition measurements to track not just your weight — but your fat mass, muscle mass, and metabolic health — so we can see what is actually happening inside your body as you lose weight.

This gives us the data to personalize your protein targets, adjust your exercise recommendations, and catch any excess muscle loss early — before it becomes a problem. It's the difference between weight loss and healthy weight loss.

A note for older adults: If you are over 60 and taking a GLP-1 medication, protecting your muscle mass is especially important. Sarcopenia — age-related muscle loss — already accelerates after 65, and significant additional muscle loss from rapid weight loss can increase your risk of falls, frailty, and loss of independence. Please discuss a personalized muscle-preservation plan with us at your next visit.

The bottom line

GLP-1 medications like semaglutide and tirzepatide are powerful and effective — but they work best when paired with the right nutrition and exercise plan. Protein and resistance training aren't optional additions to your GLP-1 regimen. They're essential parts of doing it right.

This blog is written to educate and inform — not to replace the personalized care of your physician. Every patient is different, and what's right for one person may not be right for another. Please talk to Dr. Daly, Dr. Plasencia, or your own healthcare provider before making any medical decisions based on what you read here.

Are you on a GLP-1 medication and wondering if you're protecting your muscle? Or interested in starting a medically supervised weight loss program that includes body composition monitoring? Call us at (989) 791-3401 to schedule a consultation with Dr. Daly or Dr. Plasencia. We serve patients throughout Saginaw, Bay City, Midland, and Mid-Michigan.