Dr.CardioMD said:

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…

Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. 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.

mia_MS2 said:

I lifted three times a week throughout and still lost lean mass.

DEXA scan update relevant to lean mass:

Scanned at months 0, 6, and 12. Here are the body comp numbers:

Lean mass preserved — actually GAINED 1-2 lbs thanks to progressive overload + 1.6g/kg protein. The lean mass discussion needs to include body comp data, not just scale weight.

Dr.RenalNash said:

I think this board over-worries about lean mass.

Dr.RenalNash 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.

One thing that is still open after LarryQC_SD’s answer:

Whether resistance training and protein change the ratio or only the absolute amount?

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.