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How much protein in grams do I need at 81 kg on 900 kcal a day?

Asked 5 Jun 2025Modified 10 months agoViewed 12k times
19

The case in front of me: 81 kg · 900 kcal.

Please show the division. I want to check my own against yours.

I would like the general form as well as the specific number, so I can apply it again.

How many significant figures are actually justified here?

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IP
askedivo_paunovic15k185 Jun 2025

5 Answers

Accepted answer first, then by votes
36

Accepted answer

What the data supports is narrower than what gets recommended, so it is worth separating the two.

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.

The first four weeks of loss is substantially fluid and glycogen. Each gram of stored glycogen carries roughly three grams of water, and total glycogen is on the order of 400 to 500 g, so the obligatory water shift alone accounts for a couple of kilograms. This is why the first month looks dramatic and the second looks like a plateau when in fact the fat-loss rate has not changed.

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.

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.

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

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JW
answered · acceptedj_wierzbicki45k3814 Aug 2025
Worth adding that the method section is where the answer usually is. – ilaria_bertone 4 months ago
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31

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

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.

On the detail: 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].

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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DK
answeredDr_Sara_Kuusela46k382 Aug 2025
3Does this hold at lower concentrations, or does adsorption dominate? – RP_C18 2 months ago
4Worth flagging that this changed in 2025, so older answers on the site are out of date. – meniscus_film 3 months ago
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14

To be exact about it, 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.

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, 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.

I would be careful with the supplement literature here; effect sizes are small, the studies are mostly in trained young men, and generalisation to a large deficit is not obviously valid.

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

edited 14 Jul 2025 by nynke_dekker — added the citation requested in comments

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ND
answerednynke_dekker18k2811 Jul 2025
9

It helps to be literal here: 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.

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.

The body-composition substudies in the major programmes consistently report that the proportion of weight lost as fat mass is approximately three quarters or better, with the lean-mass fraction falling within the range seen in dietary weight loss of comparable magnitude[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.

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

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LC
answeredlyoph_cake95k25816 Sept 2025
-3

To be exact about it, start with the arithmetic, because the answer to the practical question is usually a number and the number is usually achievable.

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.

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.

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

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GP
answeredg_paskevicius44k3822 Jul 2025

Your answer

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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