#398 ‒ AMA #86: GLP-1 RAs and muscle loss: new data, better questions, and how to preserve muscle during weight loss

What It Covers

Peter Attia and a colleague examine GLP-1 receptor agonists—including semaglutide drugs like Ozempic and Wegovy—and their effects on muscle and lean mass loss, bone density, fat distribution, and how exercise and nutrition modify outcomes.

Key Questions Answered

• •Lean mass loss ratio: Early GLP-1 clinical data showed roughly a 50/50 split between fat and lean mass lost—meaning a 10-pound loss yielded only 5 pounds of fat loss. Contrast this with diet-based restriction, which typically produces an 80/20 fat-to-lean ratio.
• •DEXA scan limitations: DEXA measurements of lean mass can be misleading when interpreting body composition changes on GLP-1 drugs. Clinicians should look beyond the scale and DEXA numbers toward strength and physical function metrics as more reliable indicators of true muscle health.
• •Behavior modification changes outcomes: Clinical trial averages obscure the fact that patients counseled on resistance training and adequate protein intake during GLP-1 use show meaningfully better body composition results. Nutrition and exercise guidance should be integrated into any GLP-1 treatment protocol from day one.
• •Retatrutide on the horizon: Retatrutide, a next-generation weight-loss drug moving toward FDA approval, raises new questions about muscle mass preservation. Monitoring its body composition profile—not just weight loss magnitude—will be a priority as it enters mainstream clinical use.