GLP-1 Drugs Cost Muscle at Rates Similar to Diet and Exercise Programs, Meta-Analysis Finds

Incretin-based drugs such as semaglutide and tirzepatide produce large weight reductions, and clinicians and patients worry that some of the loss is muscle. Muscle matters for strength, metabolic health, mobility and healthy ageing, so it is important to know whether these drugs are unusually harmful to lean tissue or whether any weight loss carries this cost.

The authors searched four major databases through January 2026 for randomised trials of semaglutide, tirzepatide, liraglutide or lifestyle interventions in adults with overweight or obesity. Trials had to measure body composition by DXA or MRI. The co-primary outcomes were the absolute change in lean mass and the proportion of total weight loss attributable to lean mass. Data were pooled with random-effects models, and risk of bias and certainty of evidence were assessed with RoB 2 and GRADE.

Twenty trials with 15,782 participants were included. Lean mass accounted for 35.2% of weight lost with semaglutide, 25.4% with tirzepatide and 26.8% with liraglutide. Intensive lifestyle interventions showed 26.2%, and the comparison with incretin therapy was not significant (p = 0.42). Lifestyle plus resistance training had the most favourable profile at 17.5%. Heterogeneity was moderate (I2 = 68%), and no publication bias was detected.

The findings suggest that losing some lean mass is an expected part of major weight loss, whatever the method. Muscle-protective strategies, namely resistance training, sufficient protein and body composition monitoring, should be built into treatment programs.

Several caveats apply. The comparison is indirect and across trials, not head-to-head. Lean mass measured by DXA is not the same as muscle quality or function. The semaglutide estimate was numerically higher than the others, and moderate heterogeneity limits how far the pooled figures can be applied to individual patients.