Why You Lose Muscle on Mounjaro and Ozempic — and How to Prevent It

You've started a course of Mounjaro or Ozempic and the weight is finally coming off. But here's what's rarely discussed at the start: along with fat, your body is losing muscle. And this isn't a side effect — it's the physiology of weight loss.

DXA research from SURMOUNT-1 showed that participants on tirzepatide lost 10.9% of their lean mass over 72 weeks [3]. On semaglutide, the numbers are similar — 9.7% in STEP-1 [2]. The question isn't whether you're losing muscle. The question is how much and whether you can control it.

This article is a practical protocol for preserving muscle during GLP-1 medication treatment. No fluff, just concrete numbers from clinical studies and recommendations from leading medical organizations in 2025.

Why Mounjaro and Ozempic Cause Loss of Muscle, Not Just Fat

When you lose weight — by any method — your body loses both fat and muscle tissue. This is basic caloric deficit physiology. GLP-1 medications are no exception.

The mechanism is simple. Mounjaro and Ozempic reduce appetite through brain receptors and slow stomach emptying [2]. You eat less. A caloric deficit is created automatically. And when your body doesn't receive enough energy from outside, it takes it from within — not just from fat stores.

Muscle tissue is metabolically active. It requires energy even at rest. When the body enters conservation mode, it tries to eliminate "expensive" tissues. And if you don't signal it to preserve muscle — the body gradually breaks it down for energy.

Here's an interesting point. Research shows that the proportion of muscle to fat loss on GLP-1 medications is approximately the same as on placebo with similar weight loss [3]. So the problem isn't the medications themselves — it's how you support your treatment.

How Much Muscle Is Actually Lost — DXA Data from SURMOUNT-1 and STEP-1

Let's look at specific numbers. They may seem alarming, but it's important to understand the context.

In the SURMOUNT-1 sub-study (tirzepatide, also known as Mounjaro) with DXA measurements over 72 weeks, participants showed these results [3]:

In absolute numbers, this means: minus 15.9 kg of fat and minus 5.6 kg of muscle [14]. The ratio is approximately 75% fat to 25% muscle — and this is the same for both the tirzepatide and placebo groups [23].

For semaglutide (Ozempic), data from STEP-1 shows approximately 9.7% lean mass loss [2]. And a 2026 systematic review found that lean mass can account for 25.4% (tirzepatide) to 35.2% (semaglutide) of total weight lost [10].

Interestingly, real-world data (not from clinical trials) shows something different. A 2026 study on medRxiv found that tirzepatide leads to greater absolute muscle loss compared to semaglutide at every time point [12]. At 12 months, the difference was approximately 1 kg in favor of semaglutide.

But honestly, choosing a medication based solely on this metric is a mistake. Tirzepatide produces significantly greater total weight loss (20.2% vs 13.7% in the head-to-head SURMOUNT-5 comparison) [1]. And if you properly support your treatment — muscle loss is minimized on both medications.

Why Muscle Loss Is Dangerous: Sarcopenia, Metabolism, and Weight Regain

Muscle isn't just about aesthetics. It's your metabolic engine, protection against injury, and the foundation of functionality in older age.

Research shows that adults with sarcopenic obesity have 2-3 times higher risk of losing functional independence [27]. They fall more often, break bones more frequently, and lose the ability to care for themselves faster.

This especially applies to people over 50. By age 80, sarcopenia occurs in nearly half the population [16]. And if age-related muscle loss is combined with weight loss-induced muscle loss — functional strength and mobility suffer critically.

There's also the metabolic aspect. Each kilogram of muscle tissue burns calories even at rest. After losing 5 kg of muscle, you lower your basal metabolism. This means that after completing your treatment, you need to eat even less to maintain weight. Otherwise — the weight returns.

The ENDO 2025 meta-analysis from the Endocrine Society showed that approximately 40% of weight lost on semaglutide can be muscle mass [8]. But — and this is key — this primarily occurs in those who consume insufficient protein and don't exercise.

Protein — The Foundation: How Many Grams Per Kilogram and How to Distribute

The main news of 2025: four leading medical organizations (ACLM, ASN, OMA, TOS) published joint nutrition recommendations for GLP-1 therapy [13]. And protein is in first place.

What does this mean in practice? If you weigh 80 kg (176 lbs), your daily target is 96 to 128 grams of protein. For someone weighing 100 kg (220 lbs) — 120 to 160 grams.

Now let's be honest: this is difficult. GLP-1 medications reduce appetite. Eating at all is hard, and consuming 130 grams of protein per day is a real challenge.

A research review showed a clear correlation: those who consumed less than 1.0 g/kg protein lost approximately 39% of weight as muscle. Those who consumed 1.6 g/kg or more — only 22% [32]. Almost double the difference.

Practical tips:

• Distribute protein across 3-4 meals of 30-40 grams each. The body absorbs protein better in portions rather than the entire daily amount at once
• Start each meal with protein. When appetite is reduced, it's important to eat the most valuable food first
• Use protein supplements (whey protein, casein) if you can't reach your target from food alone
• Best sources: chicken breast (31g per 100g), Greek yogurt (10g per 100g), eggs (13g per 2 eggs), cottage cheese (18g per 100g), fish (20-25g per 100g)

Leucine is especially important — the amino acid that most stimulates muscle protein synthesis. Research showed that a combination of whey protein, leucine, and vitamin D preserves significantly more muscle mass during weight loss [38].

Resistance Training 2-3 Times Per Week: What the 2025-2026 Consensus Says

Protein is the building material. But without the signal to "build," the body doesn't know why it should keep this material. That signal is resistance training.

What does research say?

A clinical case published in PMC and 2024 analysis by Neeland, Linge, and Birkenfeld confirm: structured resistance training is the main tool for muscle preservation on GLP-1 therapy [2].

Recommendations from sources:

• Frequency: 2-4 sessions per week covering all major muscle groups [36]
• Intensity: RPE (rating of perceived exertion) 7-9 out of 10 on compound exercises. Not to complete failure — close to it [2]
• Exercise type: compound movements — squats, deadlifts, presses, rows [34]
• Progression: gradual increase in weight or repetitions — the body only adapts to increasing stimulus

The LEAN-PREP study (ClinicalTrials.gov: NCT06885736) is currently investigating specific resistance training protocols combined with protein for people on semaglutide and tirzepatide [25]. Participants in the training group perform moderate-to-high intensity sessions. Results are expected soon.

Important point: fatigue on GLP-1 medications is real. You may feel less energy, especially at the beginning. Therefore:

• Include rest days between workouts for recovery [34]
• Listen to your body — 2 quality workouts are better than 4 exhausting ones
• Don't expect progress like on full nutrition — the goal now is to maintain, not gain

Creatine, Vitamins, and Peptides for Muscle Preservation (MOTS-c, Ipamorelin, Tesamorelin)

Beyond protein and training, there are additional tools. Not replacements for the basics — but useful supplements.

Creatine

Creatine is the most researched sports supplement in the world. It supports muscle energy during resistance training and aids recovery.

On GLP-1 therapy, creatine may be especially beneficial because it:

• Helps maintain strength even during caloric deficit
• Supports water balance in muscle cells
• Is safe for long-term use

Standard dose: 3-5 grams per day. A loading phase is not required.

Vitamin D

Vitamin D deficiency is associated with muscle strength loss and increased sarcopenia risk. The combination of vitamin D with protein and leucine showed better muscle preservation results in a study of people with obesity [38].

Recommendation: check your 25(OH)D blood level and maintain it between 40-60 ng/ml.

Peptides for Muscle

DOZA offers peptides that can support muscle tissue and metabolism:

• MOTS-c — a mitochondrial peptide that supports muscle energy metabolism and promotes glucose utilization. May help preserve muscle mass during weight loss
• Ipamorelin — a growth hormone secretagogue that promotes tissue recovery and supports muscle mass
• Tesamorelin — another growth hormone stimulator, researched for reducing visceral fat while preserving muscle

Promising Solutions

At the ADA 2025 conference, results from the BELIEVE study were presented — a combination of bimagrumab with semaglutide [41]. Bimagrumab blocks receptors that inhibit muscle growth. Early data shows potential for preserving muscle mass during GLP-1 therapy. Still in research stages, but a promising direction.

Practical Weekly Plan: Nutrition + Training During Treatment

Theory is good. But what does this look like in practice? Here's an example weekly plan for someone weighing 80 kg (176 lbs) on Mounjaro.

Nutrition (goal: 100-130g protein per day)

Breakfast (25-30g protein):

• 3 eggs + 100g cottage cheese
• Or: 200g Greek yogurt + 20g protein powder

Lunch (35-40g protein):

• 150g chicken breast or fish
• Vegetables of choice
• If appetite is low — at least half the protein portion

Dinner (30-35g protein):

• 150g meat or fish
• Or: 200g tofu + 2 eggs

Snack (as needed):

• 25g protein shake
• Or: 100g cottage cheese

Training (3 times per week)

Monday — Lower Body:

• Squats: 3 sets of 8-12 reps
• Romanian deadlift: 3 × 10
• Lunges: 2 × 10 each leg
• Calf raises: 3 × 15

Wednesday — Upper Body (Pulling movements):

• Bent-over row: 3 × 10
• Pull-ups or lat pulldown: 3 × 8-12
• Single-arm dumbbell row: 2 × 10
• Biceps: 2 × 12

Friday — Upper Body (Pushing movements):

• Bench press or dumbbell press: 3 × 10
• Overhead press: 3 × 10
• Dips or push-ups: 2 × max
• Triceps: 2 × 12

Intensity: RPE 7-8 (hard, but you could do 2-3 more reps).

Progression: When an exercise becomes easy — add weight or reps.

Supplements (daily)

• Creatine monohydrate: 5g
• Vitamin D3: 2000-4000 IU (or based on test results)
• Omega-3: 2g EPA+DHA

Mistakes That Cause Muscle Loss Even With Protein

Doing everything right, but still losing muscle? Check if you're making these mistakes.

1. Counting protein but not eating it

Reduced appetite on GLP-1 is a real problem. You might plan 120g of protein but actually eat 60-70g. Keep a food diary for at least the first month to see real numbers.

2. Training without progression

If you've been lifting the same 5 kg dumbbells for three months — your body sees no reason to preserve muscle for greater loads. Progressive overload is critical.

3. Too much cardio

Running, cycling, elliptical — all burn calories but don't signal muscle preservation. During a caloric deficit, excessive cardio can accelerate muscle tissue loss. Focus on resistance training.

4. Insufficient recovery

Muscles grow (or at least are maintained) during rest, not during training. If you're training 5-6 times per week without proper sleep — your body doesn't have time to recover.

5. Rapid dose increases

Moving to a higher dose of Mounjaro or Ozempic can temporarily intensify appetite suppression. During this period, reaching your protein target is especially difficult. If possible — let your body adapt gradually.

6. Ignoring signs of muscle loss

How do you know if you're losing muscle?

• Strength decreases faster than weight
• Arm and leg circumferences decrease disproportionately
• Fatigue during usual activities
• "Saggy" skin with relatively small weight loss

If you notice these signs — it's time to review your protein and training protocol. Learn more about plateaus on Mounjaro and how to overcome them.

Monitoring: How to Track Body Composition During Treatment

Scale weight is a poor indicator. You might lose 1 kg of weight, of which 0.7 kg is muscle. Or 0.9 kg is fat. The scale won't show the difference.

DXA (dual-energy X-ray absorptiometry) — the most accurate method. Shows fat mass, lean mass, and bone density separately. If possible — do it at the start of treatment and every 3-4 months [10].

Alternatives:

• Bioimpedance analysis (InBody, Tanita) — less accurate but more accessible
• Circumference measurements — waist, biceps, thigh. Simple method that shows trends
• Handgrip strength — the SEMALEAN study showed that on semaglutide, grip strength can even increase by 4 kg over 12 months with the right approach [15]

What to Do Right Now: First Month Checklist

You've read to the end. Here are specific actions for your first month:

Week 1:

• [ ] Calculate your protein target (weight × 1.2-1.6)
• [ ] Start a food diary (MyFitnessPal, FatSecret)
• [ ] Weigh yourself and measure circumferences

Week 2:

• [ ] Start resistance training 2 times per week
• [ ] Order creatine and vitamin D
• [ ] Check actual protein intake — are you hitting your target?

Week 3-4:

• [ ] Increase training to 3 times per week
• [ ] Adjust diet if protein is insufficient
• [ ] Pay attention to recovery and sleep

After one month:

• [ ] Compare circumferences
• [ ] Assess strength progression during workouts
• [ ] If possible — get a DXA or bioimpedance scan