Mounjaro has become increasingly popular for its effectiveness in driving weight loss. But as more people start using it, many are asking the same question: does it cause muscle loss alongside fat loss?
And it’s not just Mounjaro. Similar concerns have been raised about other GLP-1 medications, including Ozempic and Wegovy.
So what does the research actually say? Here’s what to know about GLP-1s and muscle loss.
Do Mounjaro and other GLP-1s cause muscle loss?
In short: yes. It’s normal to lose some muscle when losing weight, no matter how you do it.
Medications like Ozempic and Wegovy are called "GLP-1s" because they mimic GLP-1, a hormone that slows digestion, reduces appetite and regulates blood sugar. Mounjaro is slightly different as it works by mimicking GLP-1 and another hormone called GIP, which also suppresses appetite and regulates blood sugar.
Since these medications reduce overall body weight rather than only fat, some muscle loss is expected. The same thing happens with weight loss from diet or lifestyle changes alone. This is simply how weight loss works.
What do GLP-1s do to muscle?
Here's what the research shows:
They reduce total weight, not just fat
GLP-1s do not only target body fat. They reduce overall weight, which means some lean mass and muscle are usually lost alongside fat. Recent evidence suggests this may be an adaptive response, helping the body use less energy at a lower weight.
Muscle loss is proportional to weight loss
Studies suggest that the amount of muscle lost with GLP-1s is generally in line with what you would expect from any significant weight loss. It's a normal part of losing weight, not a harmful side effect of the medication itself.
They may improve muscle quality
GLP-1s might actually improve muscle function by making you more sensitive to insulin. This means your muscles can take up and use glucose more effectively, which may support better muscle function even if muscle size changes.
Strength and function often stay the same
In many trials, measures like grip strength, walking speed, and chair-stand tests stay stable during GLP-1 treatment. So although some muscle mass may be lost, day-to-day strength and mobility don't seem to drop in most people.
Can you build muscle while taking a GLP-1?
Yes, absolutely. With regular strength training and a nutritionally balanced diet (including enough protein), you can build muscle while taking GLP-1 medications. Many people see results within 6 to 8 weeks.
How to prevent muscle loss on Mounjaro (and other GLP-1s)
The good news is you can minimise muscle loss while taking GLP-1 medications. Here's how:
Prioritise strength training
Strength training is critical for muscle building and preservation. Aim for at least two sessions per week.
When you lift weights, your muscles contract and generate tension against resistance. This creates metabolic stress and controlled muscle damage, which triggers muscle repair and growth.
Eat enough protein
Think of protein as the building blocks of muscle. It's essential for growth and helps preserve the muscle you already have.
To support muscle maintenance and growth, aim for 1.2 to 1.5g of protein per kilogram of your body weight daily. Spread this across 3 to 4 meals throughout the day.
Your weight loss journey
Mounjaro muscle loss is a normal part of losing weight. But with consistent strength training and proper nutrition, you can maintain and even build muscle during your weight loss journey.
We can help you make these lifestyle changes through our weight loss programme. Your weight loss medication, including options like Mounjaro and Wegovy, will be delivered directly to you each month.
Take our quiz to see if you’re eligible.
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