Macro partitioning
Incretin-mimetic drugs (IMDs) such as semaglutide and tirzepatide cause significant skeletal muscle mass loss (≥10%) during rapid weight reduction, a loss comparable to 20 years of age-related decline.
If you are taking GLP-1 or GIP/GLP-1 drugs, expect to lose muscle along with fat. This is not just 'water weight'; it is functional tissue. To mitigate this, you must prioritize protein intake and engage in resistance training, as these are the only proven strategies to preserve muscle during rapid weight loss.
Available evidence suggests that clinical trial participants receiving IMDs for the treatment of obesity lost 10% or more of their muscle mass during the 68- to 72-week interventions, approximately equivalent to 20 years of age-related muscle loss.
Why this rating
Based on pivotal phase 3 trials (STEP-1, SURMOUNT-1) with DXA analysis, though exact muscle vs. lean mass distinction is noted as imperfect.
Source
Strategies for minimizing muscle loss during use of incretin‐mimetic drugs for treatment of obesity
Jeffrey I. Mechanick et al. · Obesity Reviews · 2024
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