The seven-time Mr. Olympia, Arnold Schwarzenegger, broke down new research that shows that GLP-1 medication can cause normal muscle loss. In his April 28 Arnold's Pump Club newsletter, he took a hit at exaggerated fear around GLP-1 and medications like Ozempic, Wegovy, and Mounjaro.

"One of the biggest concerns people have about GLP-1 medications like Ozempic, Wegovy, and Mounjaro is muscle loss. Body scans show people losing lean mass alongside fat, and that's triggered fears of weakness and frailty. New research suggests the reality is more complicated and much less alarming."

He made it clear in the Pump Club newsletter: the myth does not hold up.

These medications have spread like fire in the mainstream market in recent years, primarily because of the drastic weight loss one undergoes because of them. The medicines work by influencing blood sugar, appetite, and digestion.

But with the amazing effects, there lay a concern in fitness communities that these drugs strip lean muscle alongside fat, leaving users weaker.

Body composition scans appeared to back the worry. The numbers showed "lean mass" declining in GLP-1 users, and the fitness community took notice. Schwarzenegger did not take kindly to such an assault.

Arnold Schwarzenegger Says Muscle Loss Numbers Are Being Misread

Schwarzenegger pointed to research published just last month evaluating several GLP-1 drugs in both obese mice and a pilot human study of 10 individuals.

When tested on obese mice, GLP-1 drugs caused a bodyweight loss of 22-35% in two to four weeks. There was a moderate loss in muscle mass, ranging from 5-10%. Fat mass loss was even more pronounced at 41-73%.

The difference is astounding, with each pound of muscle lost resulting in the loss of more pounds of fat.

The human trial tracked patients with obesity and diabetes over 12 weeks. The results looked similar. Fat accounted for 70% of total weight lost, with lean body mass making up the remaining 30%.

"This is consistent with what you typically see in non-GLP-1 studies with weight loss of 20 pounds or more," said Schwarzenegger

When the scan is done for body composition, it does not isolate skeletal muscle. They take into account all lean tissue and organs. In the study Schwarzenegger highlighted, the liver shrank considerably as people lost weight and fatty liver conditions were resolved.

"That means the 'muscle loss' numbers commonly cited may overstate what's actually happening to skeletal muscle because they include changes in the liver," he wrote.

GLP-1 medications have also increased mitochondrial proteins in muscle and altered metabolism. These drugs aren't simply suppressing appetite; they are actively changing how muscle tissue adapts to the weight loss.

Schwarzenegger did not give GLP-1 users a clean chit. Even with the more optimistic picture painted by new research, he clearly stated that strength training is of utmost importance.

"If you're using GLP-1 medications — or losing a lot of weight by any method — strength training isn't optional. You need to build strength and eat enough protein to support the changes occurring in your body."

The 78-year-old ex-bodybuilder does not seem to have abandoned that philosophy. Even decades after his professional career, Schwarzenegger remains devoted to sports performance and champions resistance exercise as the key to maintaining good health.

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Written by

Proma Chatterjee

Edited by

Ashvinkumar Patil