By Joshua Shavit

Copyright thebrighterside

A new study suggests that some people taking the popular weight-loss drug Semaglutide may face an unexpected downside: loss of muscle. Older adults and women seem to be at greater risk, but researchers found that eating more protein might reduce this risk. This early research offers important insight into how weight loss with medication can affect your body in ways you might not expect.

Semaglutide, part of a class of medications called GLP-1 receptor agonists, helps people lose weight by reducing hunger and improving how the body uses insulin. It’s commonly sold under brand names like Wegovy and Ozempic. Many people taking it have seen dramatic results. However, scientists are now exploring how this drug affects more than just fat.

Muscle, also known as lean mass, plays a major role in keeping your body healthy. It helps control blood sugar after meals and keeps bones strong, especially as you age. According to lead researcher Dr. Melanie Haines from Harvard Medical School, losing too much muscle during weight loss could harm your metabolism and bone health.

“When someone loses weight, about 40% of that loss tends to come from lean mass, which includes muscle,” Haines said. That’s not just true with Semaglutide. It’s also common in traditional weight loss through diet and exercise. But it’s still unclear how to know who is most at risk or how this muscle loss affects other parts of health like blood sugar control.

To explore these concerns, Haines and her team studied 40 adults with obesity over three months. Out of the group, 23 participants were prescribed Semaglutide. The other 17 joined a structured diet and exercise program called Healthy Habits for Life, or HHL. As expected, those on Semaglutide lost more weight than the group focused only on lifestyle changes. But here’s the twist: the percentage of that weight loss that came from muscle was nearly the same in both groups.

This means that while Semaglutide may lead to faster or greater weight loss, it doesn’t reduce the chance that some of that lost weight is muscle. However, when researchers looked closer, they found that in the Semaglutide group, muscle loss wasn’t the same for everyone.

Women, older adults, and those who ate less protein lost more muscle compared to others. For these patients, greater muscle loss was also tied to weaker improvements in their blood sugar, measured through HbA1c levels—a key marker for blood sugar control over time. “Older adults and women may be more likely to lose muscle on Semaglutide, but eating more protein may help protect against this,” Haines said.

Muscle doesn’t just help you lift heavy things—it also helps burn calories, manage blood sugar, and support your bones. So losing muscle during weight loss can lead to problems, especially as people age. It can make it harder to stay active, raise the risk of falling, and even increase the chances of developing type 2 diabetes.

In the study, those who lost more muscle didn’t benefit as much from the drug’s effects on blood sugar. That could mean Semaglutide is less effective at preventing insulin resistance in those cases. Losing too much muscle might also lead to frailty later in life. These findings matter not only for doctors prescribing GLP-1 medications but also for anyone using them to manage their weight. Preserving muscle could be key to getting the full health benefits of Semaglutide.

One encouraging part of the study was the link between protein intake and muscle protection. People who ate more protein while taking Semaglutide kept more of their muscle, even as they lost fat. Protein helps rebuild and maintain muscle, especially during weight loss when the body is under extra strain. This suggests that simple changes in diet—like eating more protein-rich foods—could make a real difference for people on Semaglutide.

Dr. Haines emphasized that this is an area where more research is still needed. “Losing too much muscle may reduce the benefits of Semaglutide on blood sugar control,” she said. “This means preserving muscle during weight loss with Semaglutide may be important to reduce insulin resistance and prevent frailty in people with obesity.”

While the study was small and lasted only three months, the findings point to a larger issue that could impact the millions of people using weight-loss drugs. There’s still much to learn about how to balance fat loss with muscle protection.

This research opens the door for new questions. What is the right amount of protein for someone taking Semaglutide? Should exercise be added to protect muscle mass? Are some people more at risk than others because of their age, gender, or health history?

Dr. Haines and her team believe future studies should look at longer-term effects of Semaglutide and how different strategies can help patients lose fat while keeping their muscles strong.

As the use of GLP-1 medications continues to grow, especially among older adults, understanding how to protect muscle may become just as important as losing weight.

Research findings are available online at ENDO 2025.

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