Outcomes · Body composition · continued

Lean mass preservation: what the evidence supports — does this still hold? posts 61–90

Outcomes › Body composition bioimpedance lean mass loss data table DXA

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.

journalclub_wrenTL3Regular19 Apr 2026#61

b.correia, post #7: The arithmetic in post #6 is right; the assumption feeding it is the part to check. Having read the whole Lean mass preservation thread before replying: the question in the first post has not actually been answered yet, and three of us have answered a nearby one instead. Go to post

Picking up post #59: that is the part I would want checked first.

Marking my uncertainty on Lean mass preservation explicitly. I am confident about the direction, much less confident about the size, and not confident at all that it generalises past the case in the first post.

7 likes in reply to #7 3mo

n.cabreraTL221 Apr 2026#62

p.boateng, post #21: I will take the caveat as seriously as the claim, which is the point of putting it there. Go to post

On post #58 — agreed on the reasoning, with one qualification.

If someone has run Lean mass preservation properly I would rather read that than my own reconstruction of it. Posting mine only because the thread has gone quiet.

17 likes in reply to #21 3mo

steady_stateTL3Regular22 Apr 2026#63

Agreed on all of that, and I have nothing to add to it.

33 likes 3mo

s.vukovicTL224 Apr 2026#64

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.

0 likes 3mo

n.abernathyTL3Analytical chemist26 Apr 2026 · edited#65

orbitrap_ola, post #14: Post #12 answers the question as asked. The question underneath it is different. Filing a mild objection to the consensus on Lean mass preservation. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. Go to post

Adding the measurement that post #64 says would settle it.

Reading back through the Lean mass preservation threads from last year, the same three questions come up every time and only one of them has ever been answered properly. That seems like a documentation gap rather than a knowledge gap.

3 likes in reply to #14 3mo

h.agyemanTL227 Apr 2026#66

Lean mass preservation is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.

11 likes 3mo

dietitian_hollisTL3Dietitian29 Apr 2026#67

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

25 likes 3mo

e.halonenTL21 May 2026#68

Where I part company with post #66, and it is a narrow parting.

DXA on the same machine with the same technician has a least significant change for lean mass of roughly a kilogram, sometimes more. Below that, two scans are the same scan.

0 likes 3mo

cannula_traceTL3Regular3 May 2026#69

n.cabrera, post #62: On post #58 — agreed on the reasoning, with one qualification. If someone has run Lean mass preservation properly I would rather read that than my own reconstruction of it. Posting mine only because the thread has gone quiet. Go to post

DXA (dual-energy X-ray absorptiometry): the standard for body composition in research. Precision is roughly ±1 kg for lean mass. Two scans six months apart on the same machine with the same technician give you useful information. Two scans six weeks apart on different machines tell you about the machines.

That much is documented. The rest is how I have interpreted it.

1 like in reply to #62 3mo

v.rautioTL24 May 2026#70

Nobody has said the unglamorous part of Lean mass preservation yet, so: most of the variation is explained by things that are boring to write about and easy to check.

7 likes 3mo

glossary_checkTL2Member6 May 2026 · edited#71

v.salgado, post #45: Lean mass preservation sits at the boundary between what this community can usefully discuss and what it cannot, and I think it falls on the discussable side, narrowly. Go to post

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

3 likes in reply to #45 3mo

an.kirchnerTL28 May 2026#72

Building on post #69 rather than restating it.

Agreed on Lean mass preservation, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.

0 likes 3mo

glossary_deskTL39 May 2026#73

Collapsed as off-topic by two members at trust level 3 or above

The most useful protocol is the one you will actually repeat identically. An imperfect measurement repeated consistently beats a better one repeated carelessly.

Two people can read the same figure differently here and both be reasonable.

a.vestergaardTL211 May 2026#74

glossary_check, post #71: Noted, and thank you for writing it out rather than summarising it. Go to post

A methods point on Lean mass preservation rather than a substantive one: if the comparison is not like for like, the difference you are measuring is the difference in method.

16 likes in reply to #71 3mo

GEldridgeTL3Regular13 May 2026#75

Where I part company with post #74, and it is a narrow parting.

I have no financial interest in anything named in this thread and I want to say so before I comment on Lean mass preservation, because it is the sort of subject where it matters.

1 like 3mo

a.krastevTL214 May 2026#76

Post #74 is the version of this I will quote in future. One addition.

Percentage body fat is a ratio, so it changes when either component changes. A rising percentage during weight loss is arithmetic before it is physiology.

If anyone has run this properly I would rather read that than my own guess.

0 likes 2mo

d.bramleyTL3Regular16 May 2026#77

Genuine question rather than a rhetorical one: has anyone here actually observed Lean mass preservation, as opposed to read about it? The thread is long and I cannot tell.

23 likes 2mo

a.nascimentoTL218 May 2026#78

n.achebe, post #5: Fine by me. I had wanted a stronger conclusion and there is not one available. Go to post

Practical answer on Lean mass preservation, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.

10 likes in reply to #5 2mo

MakinenTL2Member19 May 2026#79

I had written a reply contradicting post #77 and deleted it. Here is what survived.

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

If anyone can point at the primary source I would be grateful.

0 likes 2mo

s.radichTL221 May 2026#80

Nothing to add on the substance. Thank you for taking the question at face value.

32 likes 2mo

d.nwosuTL223 May 2026#81

GDashwood, post #41: Lean mass preservation looks different depending on whether you are reading the primary literature or the summaries of it, and the difference is not in our favour. Go to post

That is a cleaner way of putting what I was circling around.

12 likes in reply to #41 2mo

e.mikkelsenTL2Member24 May 2026#82

i.bakken, post #59: 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?" Go to post

Post #79 put the caveat in the right place and I want to underline it.

My experience of Lean mass preservation contradicts the reply above. I am posting it as a data point rather than as a refutation, because one person's experience is exactly that.

25 likes in reply to #59 2mo

r.oyelaranTL226 May 2026#83

The arithmetic in post #82 is right; the assumption feeding it is the part to check.

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 would be glad to be shown a cleaner way of putting this.

0 likes 2mo

r.torrenceTL2Member27 May 2026 · edited#84

The reason Lean mass preservation keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.

4 likes 2mo

m.yildizTL229 May 2026#85

r.aldana_pharmd, post #34: DXA on the same machine with the same technician has a least significant change for lean mass of roughly a kilogram, sometimes more. Below that, two scans are the same scan. Worth reading the earlier posts in this thread before acting on mine. Go to post

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

17 likes in reply to #34 2mo

k.farrugiaTL3Regular31 May 2026#86

p.ostergaard, post #53: That reframing is the whole thing. The facts I already had. Go to post

Lean mass in these measurements includes water, so a change in hydration appears as a change in lean mass.

The confident version of this sentence would be wrong, so here is the hedged one.

0 likes in reply to #53 2mo

a.amankwahTL21 Jun 2026#87

Narrowing post #86, because the general version has more than one answer.

On Lean mass preservation: the maintained page in the documentation commons covers the general case with citations and a review date, which is more reliable than any reply here including this one.

1 like 2mo

lyophil_marginTL3Regular3 Jun 2026#88

Everything in post #84 holds. The case it does not cover is the one I have.

Answering the Lean mass preservation question as asked, then the question I think is meant. As asked: yes, with the qualification below. As meant: it depends on how the first measurement was taken.

7 likes 2mo

i.brobergTL25 Jun 2026#89

steady_state, post #63: Agreed on all of that, and I have nothing to add to it. Go to post

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

Take it as a starting point and not as a specification.

24 likes in reply to #63 2mo

KnowltonTL3Regular6 Jun 2026#90

That is consistent with mine, for whatever one more account is worth.

0 likes 2mo