Semaglutide and lean mass: DEXA scan longitudinal data

Answering the narrow version, because the broad one does not have a single answer. The intervention that works is boring and well evidenced: resistance training two to three times a week at a genuine effort, protein at 1.4 to 2.0 g/kg of reference body weight, and not making the deficit larger than the training can support. Cardio does not protect lean mass and in a deep deficit competes with recovery.

BenResearch_OR said:

The intervention that works is boring and well evidenced: resistance training two to three times a week at a genuine effort, protein at 1.4 to 2.0…

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.

Happy to go further on any of that.

MikeFit_NJ said:

Two DEXA scans eleven months apart: down 24kg total, of which the scan says 6kg was lean.

Same position here, arrived at the long way round. 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 protein. Both numbers need a caveat that matters: "lean mass" on a DEXA is not muscle. It includes water, glycogen and the lean fraction of organs, and glycogen alone carries about three grams of water per gram. A large early lean drop is mostly the glycogen and water going, which is why the first scan flatters and the second is the honest one.

From the other side of the consultation, briefly.

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].