The figures, for anyone assembling their own picture. If you are tracking this properly: same scanner, same time of day, same hydration, at least six months apart, and read grip strength or a lift number alongside it. Function is the outcome; the scan is the proxy.

Worth separating that from lean-mass preservation, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.

A narrower follow-up, since the general answer is now clear:

What fraction of loss being lean mass is actually normal, because the numbers quoted here range from 10% to 40% and cannot all be right?

PharmacoVig_BOS said:

If you are tracking this properly: same scanner, same time of day, same hydration, at least six months apart, and read grip strength or a lift number…

Adding the part of the answer the thread has not reached. 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.

OP back with an update, since a thread like this is useless without one.

Follow-up: I dropped the cardio to two easy sessions and put the effort into three real lifting sessions. The scale slowed and the scan improved.

LibrarianMeg 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.

Worth separating that from lean-mass preservation, which this thread keeps folding into the same question. They behave differently and the advice does not transfer.