DXA precision and the least significant change for lean mass posts 61–86

Confirming post #58 from a second method, which matters more than confirming it from a second person.

Photographs under fixed lighting and posture are a genuine record and are the hardest of these to standardise.

Reading it again, the caveat matters more than the finding.

I had written a reply contradicting post #61 and deleted it. Here is what survived.

I would rather this thread reach "we do not know" about DXA precision than reach a confident answer that nobody can support when asked.

Useful. I had the fact and not the reason, which turns out to be the important half.

Resting metabolic rate: body composition affects metabolic rate. As fat mass decreases and lean mass is maintained, metabolic rate is usually maintained better than with simple weight loss alone.

I changed my mind about DXA precision after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.

Coming back to post #64, because the follow-up matters more than the original answer.

Preserving lean tissue during a substantial deficit depends on protein intake and a resistance stimulus, and the evidence for both is reasonably strong.

Posting it because the silence on this was starting to look like agreement.

This follows post #66 rather than contradicting it.

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

Happy to expand any of that if it is the useful part.

Speaking only to DXA precision as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.

Maintenance phase: tracking body composition during maintenance (weight stable) is different from tracking during active loss. Changes are smaller and precision becomes more important.

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

I read post #67 twice before replying, because I had assumed the opposite.

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

The part I am sure of is shorter than the part I have written.

Post #71 answers the question as asked. The question underneath it is different.

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

Genuinely open to being wrong about this one.

Circumference measurements at marked sites, taken consistently, track composition change better than most people expect for the cost.

Where a scan disagrees with the mirror over a short period, the scan's precision limits are usually the explanation.