“25–40% of weight loss is lean muscle” is not accurate. What those analyses (STEP, SURMOUNT) actually report is loss of lean mass on DEXA—and that is not the same thing as skeletal muscle. DEXA divides the body into: 🔹Fat mass 🔹Bone 🔹Lean soft tissue That “lean” bucket includes water, glycogen, organs, connective tissue, and muscle. It is highly dynamic and shifts with caloric restriction, hydration, and glycogen depletion. So when you see “25–40% lean mass loss,” what you’re really seeing is: ➡️ fat-free tissue change—not isolated muscle loss If you want to measure actual skeletal muscle, you need CT or MRI (cross-sectional area, muscle volume, etc.). And here’s the key point: There is no consistent CT/MRI evidence showing that GLP-1–based therapies cause disproportionate skeletal muscle loss relative to expected weight loss physiology. What we do know: 🔹All weight loss (diet, surgery, pharmacotherapy) includes some lean/FFM reduction 🔹The ~25–40% range is well-described baseline physiology, not a GLP-1-specific signal 🔹The dominant effect remains preferential fat mass loss with significant metabolic benefit So this isn’t a drug-specific muscle-wasting phenomenon. It’s a misinterpretation of what DEXA actually measures. If we’re going to have strong opinions here, we should at least be precise about the difference between: lean mass, fat-free mass, and skeletal muscle Because those are not interchangeable terms—and treating them like they are leads to bad conclusions.