Protein Targets, Priced Out: What 0.8 vs 1.6 g/kg Actually Costs
Every protein conversation eventually lands on two numbers: 0.8 g/kg — the RDA — and something near 1.6 g/kg — where the training literature says added protein stops paying off on average. What the conversation rarely does is the accounting. We ran both targets on six personas through the same engine as the protein calculator, priced them against a fixed 2,000 kcal day, and wrote down what each one costs.
· 8 min read
Two numbers rule the protein debate. The first is 0.8 g/kg — the Recommended Dietary Allowance from the Institute of Medicine's 2005 DRI report, the intake set to meet the needs of nearly all healthy adults. The second is 1.6 g/kg — the fitted breakpoint in Morton et al.'s 2018 meta-analysis, the point past which total daily protein stopped predicting additional average lean-mass gain in resistance-training studies (about 1.62 g/kg/day, 95% CI 1.03–2.20), sitting mid-range in the ISSN's 2017 position stand of 1.4–2.0 g/kg for healthy exercising adults. Advice columns argue about which one is "right." This post does the accounting instead: we took the six personas from our earlier equation comparison, ran both targets through the exact engine behind the protein calculator, and priced the difference in grams, calories, and — the part nobody quotes — carbohydrate. Every figure below is a build-time output of that engine, not a hand-typed number.
The two targets, side by side
| Persona | Weight (kg) | RDA 0.8 g/kg | Training 1.6 g/kg | Protein energy @4 kcal/g | Share of a 2,000 kcal day | 1.6 g/kg in lb units | ISSN band 1.4–2.0 (g) |
|---|---|---|---|---|---|---|---|
| Man, 30, 180 cm, 80 kg | 80 | 64 g | 128 g | 256–512 | 12.8%–25.6% | ~58 g/lb | 112–160 g |
| Man, 45, 175 cm, 95 kg | 95 | 76 g | 152 g | 304–608 | 15.2%–30.4% | ~69 g/lb | 133–190 g |
| Man, 60, 172 cm, 78 kg | 78 | 62 g | 125 g | 248–500 | 12.4%–25% | ~57 g/lb | 109–156 g |
| Woman, 28, 165 cm, 60 kg | 60 | 48 g | 96 g | 192–384 | 9.6%–19.2% | ~44 g/lb | 84–120 g |
| Woman, 40, 160 cm, 75 kg | 75 | 60 g | 120 g | 240–480 | 12%–24% | ~54 g/lb | 105–150 g |
| Woman, 55, 163 cm, 68 kg | 68 | 54 g | 109 g | 216–436 | 10.8%–21.8% | ~49 g/lb | 95–136 g |
Grams = coefficient × body weight, rounded to whole grams (engine convention). Energy uses the American Atwater factor of 4 kcal/g. The 2,000 kcal frame is a standardized planning lens — see the caveats below before applying it to yourself.
What the first table shows
The same doubling of coefficient produces very different days depending on body size. Protein energy runs from 192 kcal/day at the RDA for the lightest persona to 608 kcal/day at 1.6 g/kg for the heaviest — a three-fold band that no single percentage can describe. As a share of a fixed 2,000 kcal budget, the RDA lands as low as 9.6% (the woman, 28, 165 cm, 60 kg persona) and the training target as high as 30.4% (the man, 45, 175 cm, 95 kg persona). Two boundary checks against the IOM's planning ranges fall out automatically. First, the woman, 28, 165 cm, 60 kg persona at the RDA sits below the 10% protein AMDR floor — not because the RDA is broken, but because a light body on a generic energy frame produces a small percentage. Second, the 1.6 g/kg target stays inside the 35% protein AMDR ceiling for all six personas, topping out at 30.4%: the official planning range comfortably absorbs the entire training recommendation at this budget.
The price: the bill is paid in carbohydrate
Here is the accounting everyone skips. Energy is conserved: protein and carbohydrate both yield 4 kcal/g, and a fixed budget cannot absorb extra protein for free. So pin the frame — 2,000 kcal total, fat fixed at exactly 30% of energy (600 kcal, 66.7 g) — and let carbohydrate take the remainder, exactly the allocation logic of the carb calculator's remainder mode. Upgrading each persona from 0.8 to 1.6 g/kg then produces a precise, person-specific bill:
| Persona | Carb remainder at 0.8 g/kg | Carb remainder at 1.6 g/kg | Carbs surrendered | Carb share of the day |
|---|---|---|---|---|
| Man, 30, 180 cm, 80 kg | 286 g | 222 g | 64 g | 57.2% → 44.4% |
| Man, 45, 175 cm, 95 kg | 274 g | 198 g | 76 g | 54.8% → 39.6% |
| Man, 60, 172 cm, 78 kg | 288 g | 225 g | 63 g | 57.6% → 45% |
| Woman, 28, 165 cm, 60 kg | 302 g | 254 g | 48 g | 60.4% → 50.8% |
| Woman, 40, 160 cm, 75 kg | 290 g | 230 g | 60 g | 58% → 46% |
| Woman, 55, 163 cm, 68 kg | 296 g | 241 g | 55 g | 59.2% → 48.2% |
Remainder arithmetic: C = (E − 4P − 9F) ÷ 4, with E = 2,000 kcal and F fixed at exactly 30% of energy (600 kcal; the unrounded gram value is used in the calculation, carbohydrates rounded to whole grams, percentages recomputed from rounded grams per site convention). "Carbs surrendered" = carbohydrate grams lost when protein doubles.
Read the last column: the upgrade costs 48–76 g of carbohydrate per day depending on body weight — heavier bodies buy more protein per step of coefficient, so they pay a larger absolute bill. And because both macros carry 4 kcal/g, the gram cost is exactly the protein gram increase: 64 g more protein for the man, 30, 180 cm, 80 kg persona means 64 g less carbohydrate, to the gram. Nothing mystical happens to your metabolism here; it is subtraction wearing a lab coat. Note also where the remainder lands: the man, 30, 180 cm, 80 kg and man, 45, 175 cm, 95 kg personas fall below the 45% carbohydrate AMDR floor on this fixed frame (44.4% and 39.6%) — the standard lens itself signalling that a 95 kg training body does not actually run on 2,000 kcal.
Why the two numbers coexist
The RDA and the training target were built to answer different questions, and most protein confusion is a category error between them. The 0.8 g/kg RDA (IOM 2005) asks: "what intake covers the needs of nearly all healthy adults?" — a population reference, by construction not aimed at maximizing training adaptations. The 1.4–2.0 g/kg ISSN range (Jäger et al. 2017, DOI 10.1186/s12970-017-0177-8) asks: "what range supports muscle building and repair in healthy exercising adults?" and the ~1.6 g/kg figure (Morton et al. 2018, DOI 10.1136/bjsports-2017-097608) is the fitted breakpoint of total daily protein versus lean-mass gain in pooled resistance-training studies — a group-average estimate with a 95% CI of 1.03–2.20, not a personal threshold. Neither paper says 0.8 is dangerous, and neither says 1.6 is mandatory; they describe different populations doing different things. Which question is yours determines which number is yours — and during a calorie deficit there is a third option on the protein calculator: 2.0 g/kg, the ISSN range's upper bound, where higher protein is commonly anchored while dieting to protect lean mass.
Using this without fooling yourself
Three honest caveats before the numbers leave this page. First, the 2,000 kcal frame is a standardized lens, chosen so six different bodies are priced comparably; it is not a recommendation to eat 2,000 kcal. Run the same math at your real TDEE — from the TDEE calculator — and both the percentages and the carb cost rescale immediately: at a 3,000 kcal training budget, every percentage above shrinks by a third, and the surrendered-carb column collapses toward zero. Second, the per-gram price assumes fat stays pinned; if you would rather trim fat than carbohydrate, the bill changes payees, though dropping fat far below ~20% of energy carries its own planning-range flags. Third, the gram targets anchor to current body weight as entered — the calculator states the basis and never swaps it silently, and anchoring to target weight during a cut is a legitimate declared choice, not a secret default.
The takeaway, priced
"How much protein should I eat?" has a hidden second question: "paid for out of what?" On a fixed budget, doubling your coefficient from the RDA to the training plateau costs 48–76 g of carbohydrate a day, lands protein between 9.6% and 30.4% of energy, and — on our six-persona run — stays inside every IOM planning ceiling while quietly violating two planning floors that are really budget artifacts. The number you should actually eat is the one whose bill you are willing and able to pay at your real energy budget, and the calculators exist to show that bill in full: grams, calories, share of the day, and the macro that pays the difference.