This gets cited here weekly, usually second-hand, so it is worth setting out what it does and does not establish.
There is also a quality change that the scan cannot see. Weight loss shifts fiber-type distribution toward Type I and improves mitochondrial density and insulin-stimulated glucose uptake per fiber — so the muscle you keep is metabolically better even though there is less of it. That does not make the loss irrelevant, but it explains why function often holds up better than the number suggests.
Where I think it is weakest: the subgroup findings are the part I trust least — with enough subgroups something is always significant, and these were not all pre-registered.
So the question, as narrowly as I can put it: 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. I would rather have one careful answer than five confident ones.
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.
SleepDoc_PDX said:There is also a quality change that the scan cannot see.
Agreeing with SleepDoc_PDX, and the qualification matters more than the agreement. 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.
SleepDoc_PDX said:There is also a quality change that the scan cannot see.
Pushing back on SleepDoc_PDX here. 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.
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Shop Reference StandardsAnswering the narrow version, because the broad one does not have a single answer. 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.
Dr.SportsMedIN 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…
This is my experience too, for whatever a second data point is worth.