Weight loss drugs: Utah study in mice finds ‘unexpected’ effects

SALT LAKE CITY — Researchers at the University of Utah say new weight loss drugs pose new questions about what happens to muscle mass and strength when people slim down and lose more than just fat.

The scientists are starting to get answers to those questions by studying the effects of semaglutide — the active ingredient in the popular weightloss drugs Ozempic and Wegovy — on mice.

In their study, published this month in the journal Cell Metabolism, the research team said they found “unexpected effects” when it came to lean mass, or weight that isn’t body fat.

When people taking semaglutide lose lean mass, it’s often assumed they’re losing muscle mass, said Katsu Funai, the study’s senior author.

“What we found in mice is that’s actually not really true,” Funai told KSL Monday.

The team found weight loss drugs cut lean mass by about 10%, but most of that was in tissue, like in the liver. However, “it’s not expected to really be a harmful thing,” Funai said, because organ size changees alongside weight loss without affecting the organ’s function.

A finding the research team didn’t expect: even when muscle stays about the same in size, it may get weaker in strength, Funai said.

Is that a cause for concern?

“Concern is a strong word, but we need to pay attention to it,” Funai said.

He said those over 60 years old may want to pay more attention, because loss of physical function could affect their quality of life and how long they live.

“There’s a lot lot of good, but there’s also a lot of things that we still don’t understand,” Funai said of weight loss drugs.

The biggest takeaway, Funai said, is that clinical studies on human subjects are needed. He and his colleagues are in the early stages of developing that sort of study.

“We need to measure physical function of individuals who are taking these drugs, because they may be getting weaker and we don’t really know,” Funai said.