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Onboarding calculation

Protein Efficiency Curve Methodology

How the article calculator interpolates source anchors into a simple protein-use efficiency percentage while separating absorption, muscle protein synthesis, and extended amino acid availability.

Status: Used by the protein efficiency article calculator and planned for onboarding protein explanation screens.
Last updated: June 15, 2026

Inputs and outputs

Inputs

  • Body weight
  • Sex/body-composition reference
  • Body fat percentage
  • Age
  • Goal
  • Training pattern
  • Daily protein grams
  • Protein feedings per day
  • Protein source

Outputs

  • Protein grams per feeding
  • Dose in g/kg/meal
  • Estimated protein-use efficiency percentage
  • Marginal value of the next 10 g protein
  • Low-return meal dose
  • Daily target range
  • Evidence-confidence label

Formula

reference_mass_kg = adjusted body weight from body weight and body-fat context
dose_g_per_kg = meal_protein_g / reference_mass_kg
context_target = general 0.30, active 0.34, resistance 0.40, whole_body 0.44, deficit_or_preserve +0.04, bulk +0.02
age_shift = 18-39 +0.00, 40-59 +0.03, 60-74 +0.08, 75+ +0.11
source_multiplier = whey 0.95, mixed_animal 1.00, mixed_meal 1.03, soy 1.10, plant_mixed 1.18
target_g_per_kg = clamp((context_target + age_shift) * source_multiplier, 0.24, 0.62)
half_dose = target_g_per_kg * 0.50
mps_signal = 100 * dose^hill / (dose^hill + half_dose^hill)
marginal_next_10g = mps_signal(dose + 10/reference_mass_kg) - mps_signal(dose)
protein_use_efficiency_percent = normalized marginal_next_10g against the high-efficiency zone
low_return_dose = first dose above target where marginal_next_10g < 2 signal points

Calculation steps

  1. Calculate a reference mass from body weight and body-composition context, while keeping body-weight-based source anchors visible.
  2. Convert current meal protein into grams per kilogram per meal.
  3. Shift the target dose upward for older age, whole-body resistance training, hard energy deficit, and lower-digestibility protein sources.
  4. Use a saturating curve for acute muscle protein synthesis signal, then convert the marginal value of additional grams into a simpler protein-use efficiency percentage.
  5. Show larger meals as lower marginal efficiency, not as zero absorption or automatic fat storage.

Guardrails

  • The curve is educational and does not measure personal muscle protein synthesis.
  • Protein above 30-40 grams is never described as wasted.
  • The percentage is a normalized protein-use efficiency estimate, not a literal isotope-measured fate of every gram.
  • Sex is treated mainly as a body-composition reference because direct sex-specific per-meal dose-response evidence is limited.
  • Users with kidney disease, dialysis, low eGFR, albuminuria, liver disease, pregnancy, eating disorder risk, or clinician-prescribed protein restriction need individualized guidance.

Sources

Interactive protein efficiency graph

This graph changes with age, sex/body-composition reference, body fat, goal, training pattern, meal frequency, and protein source. The green line is a simple interpolated percentage: higher means the next protein grams are still high-yield for protein synthesis and retention goals; lower means extra grams are increasingly lower-return. It is interpolated from the strongest available dose-response anchors, not a claim that every protein study in the world can be collapsed into one exact biological percentage.

Young adults, leg exercise Moore and Witard dose-response studies anchor the early plateau around 20-25 g high-quality protein for smaller exercise models.
Older adults and whole-body training Yang and Macnaughton shift the useful meal dose upward: 40 g can outperform 20 g in older men or whole-body resistance exercise.
Large meals are not zero-use Trommelen shows 100 g can produce a larger and longer response, so the curve tails downward instead of falling to zero after 40 g.
Daily range --
Current meal --
Protein-use efficiency --
Low-return starts --
Next 10 g efficiency --
Protein efficiency curve Interactive line chart showing estimated protein-use efficiency percentage by protein dose per meal. 0 0.25 0.50 0.75 1.0 g/kg/meal 100 0 Current meal Estimated protein-use % MPS signal reference Diversion pressure efficient range

This is an evidence-based teaching model, not a lab measurement.

These formulas describe how Unflame estimates onboarding targets. They are planning estimates and should be reviewed against real-world trends, user preference, symptoms, and professional guidance where relevant.