GLP-1 Medicines Promote Weight Loss While Preserving Muscle Mass and Function

Weight loss, while beneficial for obesity and metabolic syndrome, often comes with an undesirable side effect: the loss of lean muscle mass. This can negatively impact strength, metabolic rate, and overall physical function, especially in older adults. Concerns have been raised whether GLP-1 receptor agonists, a class of highly effective weight loss medications, might exacerbate this issue by causing a disproportionate reduction in muscle. This study specifically addresses whether GLP-1-induced weight loss leads to excessive muscle mass or function loss in both preclinical and clinical settings.

The study demonstrated that GLP-1 treatment effectively induced significant weight loss in both models. In obese mice, GLP-1 agonists led to an average 15-20% reduction in body weight. Crucially, body composition analysis revealed that while total body weight decreased by 18%, lean mass decreased by only 5% in the GLP-1 group, significantly better than the 10% lean mass decrease observed in pair-fed controls for a similar 18% total weight loss (p<0.01). Muscle strength, assessed by grip strength, was maintained or improved by 10-15% in GLP-1 treated mice compared to controls. > The study definitively showed that GLP-1 medicines promote weight loss without a disproportionate reduction in muscle mass or function in both obese mice and humans. In human participants, those on GLP-1 agonists achieved an average weight loss of 12-15% over 24-68 weeks. The percentage of lean body mass relative to total weight loss was preserved or even slightly increased (+0.5% to +1.2% change in lean mass percentage, p<0.05) compared to the lifestyle intervention group, which showed a -0.8% decrease. Measures of physical function, such as the 6-minute walk test, were maintained or improved by 5-8% in the GLP-1 groups, indicating no functional deficit.