09/02/2026
Muscle loss on GLP-1s gets blamed on the drug. A new mouse study suggests that's not the full story.
Obese mice were given Semaglutide alone or Semaglutide plus ketone esters for 3 weeks. The Semaglutide-only group lost about 55% of body weight, but also lost roughly 9 grams of muscle, along with signs of muscle atrophy including reduced strength and altered gene expression. The group that also received ketone esters lost less weight overall, about 36%, but lost only around 3 grams of muscle, with no meaningful difference in fat loss between groups. That's roughly 67% less muscle loss for a similar reduction in fat.
This points to something important: the muscle loss often associated with GLP-1s may not be about the medication itself. It may be about how the body handles a steep, unsupported calorie deficit, something that can happen with any rapid weight loss, GLP-1 or not.
A few caveats worth naming. This is a mouse study, and fat metabolism differs meaningfully between mice and humans. The weight loss here was also rapid and extreme, with high daily doses of both Semaglutide and ketone esters, not the gradual titration typically used in practice. This is hypothesis-generating, not conclusive.
What is well established: adequate protein intake and resistance training remain essential tools for preserving muscle during any significant weight loss.
Read the full breakdown. Link in bio.
(For educational purposes only)