As use of the popular anti-diabetic and weight-loss drug Ozempic skyrockets, so have concerns about the medication’s side effects. One side effect is loss of “lean mass”—body weight that isn’t fat—raising concerns that Ozempic could be reducing muscle mass and strength.
New research in mice suggests that muscle mass changes less than expected, but muscles may still get weaker, pointing out an urgent need for clinical studies to pin down the full effects of the popular medications.
Researchers found that Ozempic-induced weight loss decreased lean mass by about 10%. But by doing research with mice, the scientists were able to measure changes in body composition much more precisely than is possible in humans. They discovered that most of the lost lean weight wasn’t from skeletal muscles but instead from tissues like the liver, which shrunk by nearly half.
Some skeletal muscles did shrink as the mice lost weight—on average, by about 6%, not enough to explain the overall loss in lean mass. Other muscles stayed the same size.
Doing research with mice also allowed the researchers to accurately measure the strength of individual muscles. They found that for some muscles, strength decreased as the mice lost weight, even when the size of the muscle stayed roughly the same. For other muscles, strength was unchanged. It’s unknown how weight loss drugs affect this balance in people, the researchers say.
The researchers caution against extrapolating their results directly into humans, because mice and humans gain and lose weight in different ways. In people, obesity is associated with lower physical activity, but mice don’t tend to become less active when they gain weight. And the mice in this study became overweight because they ate a high-fat diet, whereas people become overweight for a wide variety of reasons that include genetics, diet, sleeping patterns, and age.
Instead of drawing a one-to-one parallel with humans, animal research like this provides crucial background information for future clinical trials, helping scientists ask the right questions to determine the full side effects and risks of medications like Ozempic.
