GLP-1 receptor agonists do not necessarily cause muscle loss; on the contrary, they could reduce muscle atrophy, inflammation, and adiposity while improving muscle endurance.

noli's read

The idea that these treatments cause systematic muscle loss is nuanced by current research. Clinical studies confirm that a loss of lean mass (which includes water, glycogen, and non-adipose tissue) accompanies any significant weight loss, which is an adaptive physiological response to a caloric deficit, and not a specific or toxic side effect of the medication. Meta-analyses and systematic reviews (e.g.) indicate that this loss is often proportional to total weight loss. Furthermore, data using magnetic resonance imaging (MRI) suggest that these medications can reduce intramyocellular steatosis (fat infiltration into muscle), which potentially improves muscle quality and function despite a reduction in overall volume. The claim that they "reduce atrophy" is, however, ambitious: while the metabolic benefits are real, the maintenance of muscle mass depends primarily on protein intake and resistance exercise (strength training), and not solely on pharmacological action.

the sources

1. 1Wilding JPH et al. (STEP 1) 2021
2. 2Jastreboff AM et al. (SURMOUNT-1) 2022
3. 3Jastreboff AM et al. 2023
4. 4Wilding JPH et al. (STEP 1 extension) 2022