Creatine kinase elevations on GLP-1 — looking for input

Short answer first, then the reasoning. 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.

Dr.SurgeonPGH said:

There is also a quality change that the scan cannot see.

Right, and protein targets should be set on a reference weight rather than current weight. Setting 1.6 g/kg on a starting weight of 130kg produces a target nobody hits on a suppressed appetite.

BethLabQueen said:

Two DEXA scans eleven months apart: down 24kg total, of which the scan says 6kg was lean.

This matches mine closely enough to be worth saying so. The intervention that works is boring and well evidenced: resistance training two to three times a week at a genuine effort, protein at 1.4 to 2.0 g/kg of reference body weight, and not making the deficit larger than the training can support. Cardio does not protect lean mass and in a deep deficit competes with recovery.

From the other side of the consultation, briefly.

Body composition tracking via bioimpedance on lean mass (InBody scan every 3 months):

Note: skeletal muscle mass dipped initially then recovered with consistent resistance training + high protein. The visceral fat reduction is where the metabolic magic happens.