ZaraB_AL said:

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

Back pain as a lean mass side effect: not from the medication itself, but from rapid body composition changes. Losing 53 lbs shifts your center of gravity and your core muscles need time to adjust.

Physical therapy has been essential. Core strengthening exercises (planks, dead bugs, bird dogs) daily for 10 minutes have eliminated my lower back pain. Your body is literally relearning how to carry itself.

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?

labquiet_amy said:

Back pain as a lean mass side effect: not from the medication itself, but from rapid body composition changes.

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

Reporting back.

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.

Dr.NephBHM_UK said:

lean mass + resistance training is the combo.

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.

Happy to go further on any of that.