Taking the question as asked, rather than the general version of it. 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.
Two DEXA scans eleven months apart: down 24kg total, of which the scan says 6kg was lean. I want to know whether that ratio is bad, normal, or simply what happens.
The narrow version of the question is 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.
Not looking for reassurance. Looking for the part I have got wrong.
Dr.ObesityMed said:There is also a quality change that the scan cannot see.
Agreed on the ranges, with the condition that a single DEXA is not a measurement, it is one draw from a distribution. Hydration status moves the lean compartment by a kilogram or more between scans, so any comparison of scans done at different times of day or different hydration states is noise.
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Shop Reference Standardsemily_PDX said:Two DEXA scans eleven months apart: down 24kg total, of which the scan says 6kg was lean.
Can confirm the pattern emily_PDX describes. 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.
From the other side of the consultation, briefly.
Back pain as a lean mass side effect: not from the medication itself, but from rapid body composition changes. Losing 53 lbs shifts your center of gravity and your core muscles need time to adjust.
Physical therapy has been essential. Core strengthening exercises (planks, dead bugs, bird dogs) daily for 10 minutes have eliminated my lower back pain. Your body is literally relearning how to carry itself.