DXA precision and the least significant change for lean mass — the long version

Absolute lean mass and lean mass as a proportion move differently and answer different questions. Report both or say which.

That matches what I was told, which is not the same as knowing it.

Post #29 describes the usual case. This is about the unusual one.

Air displacement plethysmography and hydrostatic weighing have their own precision limits and their own protocol sensitivities. None of these are exact.

Genuinely open to being wrong about this one.

Comparison to published data: the trials reported mean fat and lean mass changes. Individual results vary around that mean. Being above or below average is not a sign of something wrong.

Nothing above should be read as advice about what anyone else should do.

Post #42 is right about the mechanism and I think understates the practical bit.

Precision versus accuracy: the precision you need depends on what question you are answering. "Am I losing fat?" requires less precision than "Is my lean mass preservation within the expected range?"

A weak preference rather than a position.

Noted, and thank you for writing it out rather than summarising it.

Coming back to post #58, because the follow-up matters more than the original answer.

Bone mineral density changes with substantial weight loss are measurable and slow, and are one of the better reasons to have a baseline scan.

For what it is worth, the same held on the two occasions I checked.

This follows post #73 rather than contradicting it.

Comparing a body composition result against a population reference is a different exercise from tracking your own change, and the second is what most people want.

The arithmetic in post #85 is right; the assumption feeding it is the part to check.

Neither method is capable of detecting the month-to-month changes that people report detecting month to month.

I have said this before in a thread nobody could find, so it is worth repeating.

Visceral fat: DXA does not distinguish visceral (organ-associated) fat from subcutaneous fat. That distinction might matter but requires different imaging to measure.

I have written this out at length because the short version keeps being misread.