InsuranceTom said:

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

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.

FitDadDave said:

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

Muscle fiber type changes during GLP-1-mediated weight loss, relevant to lean mass: preliminary biopsy data suggests that weight loss shifts the skeletal muscle fiber type distribution:

• Decreased Type IIx (glycolytic, fast-twitch) fibers
• Increased Type I (oxidative, slow-twitch) fibers
• Improved mitochondrial density and function
• Enhanced insulin-stimulated glucose uptake per fiber

This "metabolic remodeling" of muscle may contribute to improved insulin sensitivity independent of total lean mass changes. The muscle you keep becomes metabolically better, even if there's less of it[1].

julia.endo said:

I think this board over-worries about lean mass.

Body composition tracking via bioimpedance on lean mass (InBody scan every 3 months):

Note: skeletal muscle mass dipped initially then recovered with consistent resistance training + high protein. The visceral fat reduction is where the metabolic magic happens.

Following on from ben_calgary — and this may be the naive question:

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

Reporting back.

Second scan under matched conditions, six months apart, same time of day: the lean number came back nearly a kilo higher than the panic scan. Strength was up throughout.