ZaraB_AL said:

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

Agreeing with ZaraB_AL, and the qualification matters more than the agreement. 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.

ZaraB_AL said:

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

Pushing back on ZaraB_AL here. I think this board over-worries about lean mass. Some lean loss is obligatory — you need less muscle to move a smaller body, and preserving mass you no longer need is not a health outcome. The question is whether strength and function held, and mine did.

This one has a reasonably settled answer, so here it is. 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.

mike_nyc said:

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…

Second this.