Tirzepatide, a dual glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist, has been recognized for its substantial efficacy in promoting weight loss among individuals with overweight and obesity. However, the implications of this weight reduction on lean mass remain inadequately understood. This narrative review evaluates the current evidence regarding tirzepatide’s impact on body composition, focusing specifically on changes in lean mass and its proxy measures.
A structured literature search identified ten studies, including randomized controlled trials, observational studies, and modeling analyses. These studies encompassed diverse populations, both with and without type 2 diabetes mellitus. Across these studies, tirzepatide consistently produced significant, dose-dependent reductions in body weight. Notably, these reductions were primarily attributed to fat mass; however, decreases in lean mass, fat-free mass, or skeletal muscle mass were observed across all studies.
The proportion of total weight loss attributable to lean mass generally ranged from 10% to 30%, which aligns with expected physiological responses to weight loss. Despite these findings, substantial heterogeneity in study design, population characteristics, and body composition assessment methods limits the ability to draw definitive conclusions about tirzepatide’s effects on lean mass.
Most studies relied on indirect measures such as bioelectrical impedance analysis, with limited use of dual-energy X-ray absorptiometry, which is considered a more accurate method for assessing body composition. Importantly, functional outcomes related to muscle mass were not assessed in these studies, leaving the clinical significance of the observed reductions in lean mass uncertain.
Overall, while tirzepatide appears to promote preferential fat loss, it is associated with some loss of lean mass. To mitigate potential adverse effects on muscle mass during treatment, strategies such as resistance training and adequate protein intake may be beneficial. However, further research is necessary to clarify these relationships and to establish effective strategies for preserving lean mass in individuals undergoing treatment with tirzepatide.
What this study does not show
This review does not provide definitive conclusions regarding the clinical significance of lean mass reductions associated with tirzepatide treatment.
Evidence scorecard
- Analytic validity: Not established
- Clinical validity: Partial
- Clinical utility: Not established