My trainer has no idea what GLP-1 is and it shows — May 2025

Short answer first, then the reasoning. The honest range is roughly 20 to 40% of total loss as lean mass without deliberate resistance training, and roughly 10 to 20% with it plus adequate protein. Both numbers need a caveat that matters: "lean mass" on a DEXA is not muscle. It includes water, glycogen and the lean fraction of organs, and glycogen alone carries about three grams of water per gram. A large early lean drop is mostly the glycogen and water going, which is why the first scan flatters and the second is the honest one.

Dr.BariatricHTX said:

The honest range is roughly 20 to 40% of total loss as lean mass without deliberate resistance training, and roughly 10 to 20% with it plus adequate…

Agreed on the ranges, with the condition that a single DEXA is not a measurement, it is one draw from a distribution. Hydration status moves the lean compartment by a kilogram or more between scans, so any comparison of scans done at different times of day or different hydration states is noise.

wendy_avl said:

I lifted three times a week throughout and still lost lean mass.

This matches mine closely enough to be worth saying so. There is also a quality change that the scan cannot see. Weight loss shifts fiber-type distribution toward Type I and improves mitochondrial density and insulin-stimulated glucose uptake per fiber — so the muscle you keep is metabolically better even though there is less of it. That does not make the loss irrelevant, but it explains why function often holds up better than the number suggests.

Adding the clinical framing, because it changes how the question reads.

OMG yes. lean mass + resistance training is the combo. Can confirm.