Dr.GastroMayo said:

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

Dr.GastroMayo said:

...the muscle loss concern with lean mass...

This is a legitimate and well-studied concern. Let me put some numbers on it:

In STEP 1, approximately 39% of weight lost was lean mass. However, the Lundgren 2024 study showed that structured resistance training reduced this to ~25% lean mass loss.

Context matters: at BMI 35+, you're carrying excess lean mass to support the extra weight. Losing some lean mass is expected and not inherently harmful if you maintain adequate muscle function through exercise.

The solution isn't avoiding the medication — it's combining it with proper exercise and protein intake.

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?

wendy_avl said:

Dr.GastroMayo said: ...the muscle loss concern with lean mass...

Regarding lean mass: I accidentally injected my dose intramuscularly instead of subcutaneously last week (went in at wrong angle, too deep). Called my pharmacist — they said it's not dangerous but may absorb faster, potentially causing more GI effects.

Sure enough, had worse nausea that day. Lesson learned: pinch the skin properly and use the right needle length for your body composition.

Closing the loop on my own question.

Second scan under matched conditions came back with the lean number nearly a kilogram higher than the first, so a chunk of what I panicked about was hydration. Strength numbers were up throughout.

LibrarianMeg said:

Regarding lean mass: I accidentally injected my dose intramuscularly instead of subcutaneously last week (went in at wrong angle, too deep).

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.