GLP-1 receptor agonists – medications like semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro) have transformed the way we approach weight management. But alongside the impressive results, a concern has emerged: are these drugs causing us to lose muscle?
It’s a question worth taking seriously. Muscle mass isn’t just about aesthetics – it’s central to metabolic health, strength, balance, bone density, and long-term independence.
The short answer is: not directly – but the weight loss they drive can, if it’s not managed well.
GLP-1 receptor agonists work primarily by suppressing appetite and slowing gastric emptying. This leads to a reduction in hunger and overall energy intake, creating a sustained calorie deficit.
That deficit is what drives weight loss. And here’s the key point: any significant weight loss – whether through medication, surgery, or dieting – carries a risk of losing some lean mass alongside fat. This isn’t unique to GLP-1s; it’s a well-established physiological response to caloric restriction (Neeland et al., 2024).
Clinical trials do show that lean mass loss occurs during GLP-1 treatment. Studies report that anywhere from 15% to 40% – and in some cases up to 60% – of total weight lost can come from lean mass, depending on the individual, the drug, and critically, what lifestyle behaviours accompany treatment (Neeland et al., 2024; Karakasis et al., 2025).
This significant variation raises an important question: Why is there such a large range of lean mass lost?
GLP-1 medications reduce appetite which can lead to inadequate calorie and protein consumption, lower energy levels for exercise and reduced engagement in resistance training. In other words, the biggest driver of muscle loss are inactivity and under-fuelling, not the medication itself.
The bottom line: GLP-1 medications do not inherently cause muscle loss. However, they can create conditions – reduced appetite, lower food intake, rapid weight loss – where muscle loss becomes more likely if protective behaviours aren’t in place.
How to Protect Your Muscle Mass – 6 Key Strategies
The good news is that muscle loss during GLP-1 therapy is largely preventable with the right approach.
- Prioritise Protein – and Distribute It Throughout the Day
Protein is the single most important nutritional lever for preserving muscle during weight loss. Aim for 1.2 to 1.6 grams of protein per kilogram of body weight per day for people actively losing weight, up to 1.8 g/kg for older adults.
Because GLP-1 medications can reduce overall appetite and shift food preferences, it’s easy to under-eat protein without realising it. Aim to include a quality protein source at every meal, for example – lean meats, fish, eggs, dairy, legumes, tofu, or tempeh – and aim for roughly 30 grams per meal to maximise muscle protein synthesis throughout the day.
- Resistance Train Consistently
This is non-negotiable. Muscle tissue is preserved when it is being challenged. Without progressive resistance training, your body has little reason to hold onto muscle during a caloric deficit.
Aim for at least 2-3 resistance training sessions per week, targeting major muscle groups. This could include bodyweight training, resistance bands, free weights, or machine-based exercises. The key is consistency and progressive challenge over time.
- Don’t Rely on Weight Alone as a Metric
Scale weight doesn’t distinguish between fat and muscle. Where possible, track:
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- Body composition
- Strength progression
- Functional capacity
This shifts the focus from simply “losing weight” to improving overall body composition and health. Click here to learn more about tracking body composition via DEXA scans or click here to learn about functional strength testing.
- Support Energy for Movement
Some individuals experience fatigue or reduced exercise tolerance on GLP-1s. This can become a barrier to training. Strategies may include:
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- Timing meals or protein intake around workouts
- Adjusting training intensity temporarily
- Ensuring overall energy intake is not excessively restrictive
- Consider Working with a Dietitian
Given the appetite-suppressing effects of GLP-1 medications, individualised nutrition support can make a significant difference. A dietitian can help you meet your protein targets, ensure you’re getting adequate micronutrients (particularly important when eating less overall), and adjust your intake as your weight changes.
- Take a Structured, Supported Approach
People tend to do best when GLP-1 treatment is part of a broader plan that includes nutrition guidance, exercise programming, ongoing coaching and accountability.
This is where healthcare providers can make a significant difference. Find out more about our team of accredited exercise physiologists, dietitians and executive health coaches.
The Take-Home Message
GLP-1 medications are a powerful and effective tool for weight management. The concern around muscle loss is real and worth taking seriously – but it is not inevitable. The research is clear: the extent of lean mass loss depends far more on lifestyle behaviours than on the medication itself.
Eat enough protein. Lift weights. Stay active. Fuel your training. And if you need support getting those pieces right, that’s exactly what we’re here for at Oracle Healthcare.
Wriiten by Shivaun Conn
BSc Nut. HONS APD AN
References:
- Neeland, I.J., Linge, J., Birkenfeld, A.L. (2024). Changes in lean body mass with glucagon-like peptide-1-based therapies and mitigation strategies. Diabetes Obesity and Metabolism. https://doi:10.1111/dom.15728
- Karakasis, P., Patoulias, D., Fragakis, N., & Mantzoros, C. S. (2025). Effect of glucagon-like peptide-1 receptor agonists and co-agonists on body composition: Systematic review and network meta-analysis. Metabolism, 164, 156113. https://doi.org/10.1016/j.metabol.2024.156113
