Semaglutide melts fat—but may quietly strip away your strength

Losing muscle (or lean mass) is a common side effect of weight loss in adults with obesity and may negatively affect metabolism and bone health. This is because muscle helps control blood sugar after meals and plays an important role in keeping bones strong, according to study lead researcher Melanie Haines, M.D., of Massachusetts General Hospital and Harvard Medical School in Boston, Mass.

Approximately 40% of the weight lost from taking semaglutide — a type of weight-loss medication known as a GLP-1 — comes from lean mass, including muscle. It is not yet known who is at highest risk for muscle loss or how it affects blood sugar levels, Haines said.

The researchers studied 40 adults with obesity for three months. Of these patients, 23 were prescribed semaglutide, while 17 followed a diet and lifestyle program for weight loss called Healthy Habits for Life (HHL). The researchers evaluated how their muscle mass changed.

Study participants who were prescribed semaglutide lost more weight than those who participated in the diet and lifestyle program, but the percent of weight loss that was lean mass was similar between the two groups.

After accounting for weight loss, the researchers found that in the semaglutide group, being older, female or eating less protein was linked to greater muscle loss. Also in this group, losing more muscle was linked to less improvement in blood sugar (HbA1c levels).

“Older adults and women may be more likely to lose muscle on semaglutide, but eating more protein may help protect against this,” Haines said. “Losing too much muscle may reduce the benefits of semaglutide on blood sugar control. This means preserving muscle during weight loss with semaglutide may be important to reduce insulin resistance and prevent frailty in people with obesity.”

Haines said that more studies are needed to find the best way to lose fat but keep muscle when using GLP-1 medications.