TirzTom said:

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

I read this differently from TirzTom, on substance rather than tone. 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.

nick_newbie said:

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

Bone density monitoring on lean mass: DEXA bone density at baseline and month 12.

Lumbar spine T-score: -0.12 → -0.8 (stable to slightly improved)
Femoral neck T-score: -0.13 → -0.9 (stable)

No significant bone loss despite 54 lbs of weight loss. Key factors: adequate calcium (1200mg/day), vitamin D (5000 IU/day), resistance training 3x/week, and adequate protein. Weight-bearing exercise is critical for maintaining bone density during rapid weight loss.

LibrarianMeg said:

I think this board over-worries about lean mass.

LibrarianMeg 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 RunnerRach’s answer:

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?

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.