A feature in Women's Health reports that the warnings about GLP-1 drugs destroying muscle have gotten ahead of the evidence, and that most of the research behind the alarm measured something broader than muscle. The drugs involved include semaglutide (sold as Ozempic and Wegovy) and tirzepatide (Zepbound), both widely prescribed for obesity and type 2 diabetes.

Lean mass is not muscle

The alarm traces largely to two body composition substudies: STEP 1 on semaglutide in 2021 and SURMOUNT-1 on tirzepatide in 2025, which each found participants lost around 10 percent of lean body mass. Lean body mass is everything in the body that is not fat, including organs, water and connective tissue, and Henning Langer, head of the Muscle Wasting Laboratory at Charite in Berlin, estimates only about half of it is actually muscle.

Stuart Phillips, chair of kinesiology at McMaster University, points out that the liver shrinks quickly during weight loss as it burns stored glycogen, and glycogen holds water. That shows up on a scan as lost lean mass without the same amount of lost muscle tissue.

Size fell, strength held

Langer's study, published this spring in Cell Reports Medicine, was among the first to measure muscle size and strength directly rather than lean mass alone. It followed 10 men taking semaglutide for 12 weeks: their thigh muscles shrank slightly, while grip strength and knee extension against resistance stayed the same.

Langer suggests some of that size reduction may have come from fat, stored carbohydrate and water inside the muscle rather than from the working tissue. His verdict is measured: there does not seem to be anything particularly negative about the type of weight loss achieved with these medicines.

Limitations

Ten men over 12 weeks is a very small, very short study, and no women were enrolled. Langer says it cannot speak to older adults or to people with heart failure, cancer or neuromuscular disease, and that bigger studies following people for longer are needed.

Who clinicians still watch

Robert F. Kushner of Northwestern names patients over 65, those with chronic kidney or heart disease, those starting with low muscle mass, and those losing weight unusually fast. Pooja Gidwani adds women in perimenopause and after menopause, where estrogen changes affect bone and body composition.

Bottom line

Phillips frames the goal as high-quality weight loss, meaning fat lost while strength and function are preserved, which the scale cannot measure. His sharpest line is also the most useful one: a higher lean-mass percentage is not a muscle-preservation certificate.