Scientists warn of muscle loss during rapid weight loss—here's how to stay strong
As someone who has spent over two decades studying muscle metabolism—from my PhD to my time as faculty at Harvard—I’ve seen firsthand the incredible role muscle plays in our health and performance. Muscle isn’t just about strength; it’s essential for metabolism, function, and your long-term healthspan. That’s why a new concern has caught my attention—and it’s one many people on weight loss drugs like Ozempic, Wegovy, and Mounjaro might not realize.
While these drugs have transformed the weight loss landscape, helping people shed pounds rapidly, a recent scientific review that analyzed seven major clinical trials has raised an important red flag: disproportionate lean muscle loss. In clinical trials, participants on these drugs lost as much as 10% or more of their muscle mass over the course of treatment. To put that into perspective, that’s the equivalent of losing two decades of muscle mass in just 68 to 72 weeks. This isn't just about fat disappearing—it's about losing the muscle that helps keep your metabolism running and your body functioning optimally.
Why Muscle Loss Matters More Than You Think
If you think muscle loss only negatively affects athletes, think again. Muscle is your body’s metabolic engine. It burns calories, regulates blood sugar, and powers you through everyday tasks. Losing muscle doesn’t just make you weaker—it slows down your metabolism, making it harder to keep the weight off and leading to what’s called sarcopenic obesity. This condition happens when muscle decreases while fat increases, and it’s linked to higher risks of diabetes, heart disease, and a range of other health problems. So, it’s not just about how you look—it’s about how well your body is functioning and how efficiently you burn calories.
How Do Ozempic, Wegovy, and Mounjaro Cause Muscle Loss?
Here’s where things get tricky. These weight loss drugs work by suppressing appetite, making it easier to eat less and lose weight. But when calorie intake drops significantly, your body can start losing muscle along with fat. Muscle is metabolically expensive to maintain, so when your body isn’t getting enough fuel from food, it makes cuts—and muscle is often the first to go.
In clinical trials, participants lost up to 40% of their total weight from lean body mass, which includes muscle. Since muscle is the most metabolically active tissue in your body, losing it slows down your metabolism even further. And here’s the kicker: when patients stop taking the medication, they often regain the fat—but not the muscle they’ve lost. This sets up a vicious cycle of fat regain and muscle loss, making it harder to maintain a healthy weight in the future.
(Photo: Obesity Reviews; STEP-1 (semaglutide), SURMOUNT-1 (tirzepatide))
How to Keep Your Muscle While Losing Weight
Luckily, there are steps you can take to minimize muscle loss while benefiting from the fat-shedding effects of these drugs. It comes down to two main key factors: nutrition and exercise—and doing them right. In fact, the most effective way to stimulate muscle maintenance is the combination of ingesting protein and using your muscles.
- Eat More Protein
The typical recommendation for protein intake—0.8 grams per kilogram of body weight—is simply too low, especially if you’re trying to lose weight. I recommend aiming closer to 1.5 grams per kilogram of body weight to help protect your muscle. For a 70 kg (154 lb) individual, that means consuming around 84 to 105 grams of protein per day.
To maximize muscle preservation, it’s important to spread protein intake evenly across meals, ensuring around 20-25 grams of protein per meal. This strategy helps stimulate muscle protein synthesis throughout the day, which is essential when overall calorie intake is reduced.
Given that GLP-1 drugs suppress appetite, getting enough protein through whole foods can be a challenge. This is where protein supplements become a practical tool. Adding a protein or essential amino acid supplement can help meet your daily protein and amino acid needs without feeling overly full—a consideration when appetite is lower than usual due to the medications.
- Prioritize Resistance Training
While cardio is fantastic for heart health, resistance training is critical if you want to preserve muscle. Whether it’s lifting weights, using resistance bands, or doing bodyweight exercises, resistance training helps maintain and build muscle, even while you’re losing fat. Aim for at least three sessions a week covering upper and lower body regions to see significant benefits. Studies consistently show that resistance training is the most effective way to prevent muscle loss during calorie restriction.
What the Science Says
The research on muscle loss with drugs like Ozempic and Wegovy is still evolving, but the early data is clear: rapid weight loss can lead to disproportionate muscle loss if you’re not careful. In one study, during a 68-week treatment with semaglutide (the active ingredient in Ozempic and Wegovy), participants lost 17.3 kg of body weight on average. But here’s the alarming part: 40% of that weight loss came from lean body mass, which includes muscle. Another trial with tirzepatide (branded as Mounjaro) showed similar results, with 10.9% of weight loss coming from lean mass during a 72-week intervention.
The takeaway? Weight loss isn’t just about seeing the numbers drop on the scale—it’s about preserving the muscle that keeps you healthy and strong. Without it, you could end up with a slower metabolism and a higher likelihood of regaining the weight you lost.
If you’re using drugs like Ozempic, Wegovy, or Mounjaro, take active steps to preserve your muscle while losing fat. Focus on protein intake, resistance training, and the right nutritional strategies to protect your strength—and set yourself up for long-term success.