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Does a DEXA repeated every six weeks give me an usable lean-mass trend?

Asked 12 May 2025Modified 11 months agoViewed 4.7k times
4

I would like to know what to measure as much as what to do.

I would like the axes of comparison first and the recommendation second.

I have tried the first option and it works; the question is whether the second is better rather than merely different.

Is there a defensible reason to prefer one, or is this a coin flip?

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DT
askedday_seven_trough11k1712 May 2025

5 Answers

Accepted answer first, then by votes
46

Accepted answer

More usefully, the mechanism is worth having straight, because it predicts which interventions can work and which cannot.

DEXA precision is better than people assume for fat mass and worse than people assume for lean mass in a single scan — the least significant change for regional lean mass on a well-maintained scanner is on the order of a few per cent. That means two scans three months apart can differ without anything having happened, and it means a scan sequence needs to be at least three points before a trend is interpretable.

Protein target arithmetic

Body mass1.2 g/kg1.6 g/kg2.0 g/kgPer meal at 1.6 (÷3)
62 kg74 g99 g124 g33 g
74 kg89 g118 g148 g39 g
88 kg106 g141 g176 g47 g
103 kg124 g165 g206 g55 g
124 kg149 g198 g248 g66 g

At roughly 4 kcal per gram, 141 g of protein is about 564 kcal — a substantial fraction of a 900 kcal budget, which is the real constraint.

Specifically, the regain trajectory after stopping is roughly a mirror of the loss trajectory, and it is not primarily a willpower phenomenon. Appetite signalling returns, energy expenditure remains suppressed relative to the original mass, and the two combine. That is an argument for a maintenance plan existing before the stop, rather than an argument against stopping.

The evidence for a higher protein intake preserving lean mass during an energy deficit is reasonably strong in resistance-trained populations and weaker in sedentary ones, with the meta-analytic estimates supporting intakes in the region of 1.6 g/kg over lower intakes when training is present[1].

One qualification: none of this is a clinical assessment, and unexplained loss of function rather than of mass is a reason to see someone rather than to adjust a programme.

Measure strength as well as mass. It is cheaper, it is less noisy, and it is closer to what you actually care about.

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VV
answered · acceptedvoid_volume13k1610 Aug 2025
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53

It helps to be literal here: the distinction that resolves this is between proportional loss and functional loss. Losing lean mass in proportion to total mass is what happens in every weight loss intervention. Losing function is not, and function is measurable.

Absolute strength holds up better than scale weight during a deficit for a straightforward reason: strength is substantially neural and skill-based, and the contractile tissue you retain is being trained harder relative to its size. Grip strength and repetition maxima are therefore lagging indicators of muscle loss rather than leading ones, which is an argument for measuring both.

Protein target, worked: at 88 kg, a target of 1.6 g/kg is 88 × 1.6 = 141 g per day. Spread across three eating occasions that is roughly 47 g each, and the leucine threshold for a maximal muscle protein synthetic response is met at around 2.5 to 3 g of leucine, which corresponds to roughly 30 to 40 g of a high-quality protein. So three meals at 40 g plus one 25 g snack gets you to 145 g and clears the per-meal threshold each time. On 900 kcal that leaves about 340 kcal for everything else, which is the actual constraint.

Worth stating that a DEXA sequence is only as good as its protocol consistency, and most people’s sequences are not consistent enough to support the conclusions drawn from them.

Train, eat the protein, measure something functional, and give the trend three months before you interpret it.

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VR
answeredv_ramaswamy40k381 Sept 2025
6This is the first explanation of that which has actually made sense to me. – tess_amankwah 8 months ago
7Note that the label instructions differ between agents on precisely this point. – tandem_gradient 10 months ago
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35

The commonly quoted figures for lean-mass loss are mostly measurement artefacts, and the artefact is well understood: fat-free mass as measured includes water and glycogen, both of which fall early and neither of which is contractile tissue.

Fibre at very low total intake is a trap. Soluble fibre needs water and motility to work; insoluble fibre adds bulk to a slow transit. At 900 kcal a day with delayed gastric emptying, an osmotic agent is more predictable than a bulking one, and adequate fluid is doing more work than either.

Food noise returning is not obviously tolerance. Receptor desensitisation is one hypothesis; a second is that the initial effect was partly novelty and partly the steep early deficit, and a third is that intake has drifted upward and the signal is being outcompeted rather than weakened. The three make different predictions about what a dose increase would do.

Adaptive thermogenesis — a fall in energy expenditure beyond that predicted by the change in body composition — is documented across weight-loss interventions and is the mechanistic basis for the plateau being expected rather than anomalous.

The plateau is arithmetic. Treat it as arithmetic and the response follows.

edited 4 Jun 2025 by orla_ferriter — reworded for clarity after a comment

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OF
answeredorla_ferriter47k3816 May 2025
4Minor: the trial name is hyphenated in the original publication. – e_dziedzic 3 months ago
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The underlying point is that a plateau at four to six months is the expected shape of the curve, not a failure of it. Energy expenditure falls with mass, and the deficit closes itself unless intake falls further.

Cardio does not interfere with lean-mass retention at the volumes anyone here is doing; the interference effect in the literature appears at high concurrent volumes in trained athletes. What cardio does at a large deficit is add to the deficit, which is either the point or a problem depending on the objective.

The STEP 1 extension reported substantial regain in the year after treatment withdrawal, with weight and cardiometabolic variables trending back toward baseline[1].

A maintenance plan written before you need it is worth more than a better loss plan.

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TO
answeredt_oyelaran41k3821 Aug 2025
16

On the detail: start with the arithmetic, because the answer to the practical question is usually a number and the number is usually achievable.

The minimum effective resistance-training dose in a deficit is lower than most programmes assume. Two sessions a week covering the major movement patterns, with loads taken close to failure, is sufficient to retain most of what would otherwise be lost. Volume beyond that adds recovery cost that a large energy deficit is poorly placed to pay.

The limitation of the arithmetic is that it assumes intake is being measured accurately, and self-reported intake is systematically underestimated by a substantial margin.

Two resistance sessions a week and a protein target you actually hit will do more than any refinement beyond them.

edited 3 Jul 2025 by Dr_Rosalind_Achebe — added a caveat about sampling

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DA
answeredDr_Rosalind_Achebe90k15818 Jun 2025

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Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.

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