A recent study published on medRxiv indicates that tirzepatide medications, such as Mounjaro and Zepbound, may lead to a greater loss of lean body mass compared to semaglutide medications like Ozempic and Wegovy. This finding suggests a potential trade-off for the more significant weight loss often achieved with tirzepatide.
Understanding Lean Body Mass
Lean body mass encompasses muscles, connective tissues, and other vital components that are crucial for metabolism, strength, and overall physical function. Preserving lean body mass is important as it contributes to energy expenditure and metabolic health.
Study Findings on Lean Body Mass Loss
The preprint study, which has not yet undergone peer review, analyzed data from 7,965 individuals initiating GLP-1 medications. Of these, 6,196 used semaglutide and 1,769 used tirzepatide. Researchers measured lean body mass before and after treatment. The findings revealed that individuals on tirzepatide experienced a greater loss of lean body mass. In the first three months, tirzepatide users lost approximately 1.1% more lean body mass than semaglutide users, a figure that increased to 2% more by the 12-month mark.
Why Muscle Loss Matters and Risk Factors
The loss of muscle, a significant component of lean body mass, can lead to fatigue, reduced physical performance, and an increased risk of injury. Factors that may heighten the risk of lean body mass loss while using GLP-1s include higher medication doses, longer treatment durations, lower exercise tolerance during treatment, and pre-existing musculoskeletal conditions. Approximately 10% of tirzepatide users experienced a 5% reduction in lean body mass alongside a 20% weight reduction, compared to about 7% of semaglutide users.
Strategies for Managing Lean Body Mass Loss
Experts emphasize the importance of incorporating physical activity, particularly strength training, while using GLP-1 medications to help preserve lean muscle mass. Dr. Jeffrey Lee, a plastic surgeon, stated, “Exercise (particularly strength training) plays a critical role in preserving lean muscle mass while on GLP-1 medications.” He added that resistance training signals the body to maintain muscle, even during a calorie deficit, making it a vital part of any weight loss plan involving these drugs. Dr. Mir Ali, a bariatric surgeon, also highlighted the significance of adequate protein intake and gradual weight loss. “Just as important is the pace of weight loss — slower, more gradual weight reduction tends to better preserve lean mass compared to rapid weight loss,” he noted, underscoring the need for careful dose titration and ongoing monitoring.
