Protein Quality Metrics: PDCAAS vs DIAAS — What Actually Matters in Formulation
Protein quality metrics are often treated as verdicts.
A number appears. A score is assigned. A protein is labeled “high quality” or “inferior”.
From a manufacturing point of view, that interpretation is deeply misleading.
PDCAAS and DIAAS are measurement tools, not formulation guides. They answer specific nutritional questions — but they say very little about whether a protein will behave well in a real product.
Understanding what these scores actually mean — and what they deliberately ignore — is essential if you want to design protein systems rather than chase numbers.
PDCAAS and DIAAS are measurement tools, not formulation guides. They answer specific nutritional questions — but they say very little about whether a protein will behave well in a real product.
Understanding what these scores actually mean — and what they deliberately ignore — is essential if you want to design protein systems rather than chase numbers.
What PDCAAS Was Designed to Do
PDCAAS (Protein Digestibility-Corrected Amino Acid Score) was introduced to answer a single question:
Does this protein provide essential amino acids in sufficient amounts after digestion?
Does this protein provide essential amino acids in sufficient amounts after digestion?
- It compares a protein’s amino acid profile to a reference pattern and then corrects the result based on overall digestibility. The score is capped at 1.0, meaning anything above the reference requirement is flattened.
- From a regulatory and public-health perspective, this made sense. It allowed policymakers to compare proteins and ensure minimum nutritional adequacy.
- From a formulation perspective, it already introduces distortion.
Once scores are capped, differences between proteins disappear. A whey isolate and a perfectly engineered milk protein system may both score 1.0 — despite behaving completely differently in digestion kinetics, mouthfeel, and real-world use.
PDCAAS tells you whether a protein is adequate.
It does not tell you how it performs.
It does not tell you how it performs.
How PDCAAS is Calculated: Explanation
To calculate PDCAAS, you need data on the protein's amino acid profile and its digestibility factor.
Determine the Amino Acid Composition:
The amount of each essential amino acid (EAA) in the protein source, expressed in mg per gram of protein. The nine EAAs are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Calculate the Amino Acid Score (AAS) for Each EAA:
- Use the FAO/WHO reference pattern for adults (in mg/g protein):
Histidine: 15, Isoleucine: 30, Leucine: 59, Lysine: 45, Methionine: 16 (or Methionine + Cystine: 22), Phenylalanine + Tyrosine: 30, Threonine: 23, Tryptophan: 6, Valine: 39.
- For each EAA: AAS = (mg of EAA in 1g of test protein) / (mg of EAA in reference pattern for 1g).
- Example: If a protein has 50 mg lysine per g, AAS for lysine = 50 / 45 ≈ 1.11.
Histidine: 15, Isoleucine: 30, Leucine: 59, Lysine: 45, Methionine: 16 (or Methionine + Cystine: 22), Phenylalanine + Tyrosine: 30, Threonine: 23, Tryptophan: 6, Valine: 39.
- For each EAA: AAS = (mg of EAA in 1g of test protein) / (mg of EAA in reference pattern for 1g).
- Example: If a protein has 50 mg lysine per g, AAS for lysine = 50 / 45 ≈ 1.11.
Identify the Limiting Amino Acid Score:
The overall AAS is the lowest individual AAS among the EAAs (the "limiting" one). If any AAS is below 1, it caps the score.
- Continuing the example: If lysine AAS is 1.11 but tryptophan is 0.80 (lowest), then AAS = 0.80.
- Continuing the example: If lysine AAS is 1.11 but tryptophan is 0.80 (lowest), then AAS = 0.80.
Factor in Protein Digestibility:
Use the true fecal digestibility (FTPD), a percentage based on how much of the protein is absorbed (e.g., 92% or 0.92 for whey, 85% or 0.85 for beans). This is often from standardized.
Compute PDCAAS:
PDCAAS = AAS × FTPD.
- Example: If AAS = 0.80 and FTPD = 0.92, PDCAAS = 0.80 × 0.92 = 0.736 (or 73.6%).
- Truncate if over 1: PDCAAS is capped at 1.0 (perfect score), even if calculations exceed it.
- Example: If AAS = 0.80 and FTPD = 0.92, PDCAAS = 0.80 × 0.92 = 0.736 (or 73.6%).
- Truncate if over 1: PDCAAS is capped at 1.0 (perfect score), even if calculations exceed it.
For blended proteins (e.g., in foods), average the contributions weighted by each protein's amount, then apply the steps.
This method has limitations (e.g., doesn't account for anti-nutritional factors or overvalues some proteins), but it's standard for %DV on labels.
This method has limitations (e.g., doesn't account for anti-nutritional factors or overvalues some proteins), but it's standard for %DV on labels.
Why DIAAS Was Introduced
DIAAS (Digestible Indispensable Amino Acid Score) was created to fix known weaknesses in PDCAAS.
Instead of using total protein digestibility, DIAAS measures digestibility of individual essential amino acids at the end of the small intestine. It does not cap scores, allowing proteins to exceed the reference value.
Scientifically, this is an improvement.
Nutritionally, it gives a more precise picture of amino acid availability.
But here is the critical point:
DIAAS still measures nutrient absorption, not product behavior.
It tells you how efficiently amino acids are absorbed — not how fast they are released, not how the protein feels when consumed, and not whether the formulation survives processing, storage, or consumer handling
Scientifically, this is an improvement.
Nutritionally, it gives a more precise picture of amino acid availability.
But here is the critical point:
DIAAS still measures nutrient absorption, not product behavior.
It tells you how efficiently amino acids are absorbed — not how fast they are released, not how the protein feels when consumed, and not whether the formulation survives processing, storage, or consumer handling
DIAAS requires lab data on the protein's amino acid profile and ileal digestibility coefficients (from human, pig, or rat studies, as pigs are a good model for human digestion).
Example how DAAS can be calculated:
Determine the Digestible Indispensable Amino Acid Content:
For each of the nine IAAs (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine—note: cysteine and tyrosine are considered with methionine and phenylalanine), calculate the digestible amount in mg per gram of protein.
Select the Reference Pattern: Use the FAO-recommended IAA requirements per gram of protein, adjusted for age groups (e.g., infants, children, adults).
For adults (the most common): Histidine: 10 mg/g, Isoleucine: 20, Leucine: 39, Lysine: 30, Methionine: 10.4 (or Methionine + Cystine: 15), Phenylalanine + Tyrosine: 25, Threonine: 15, Tryptophan: 4, Valine: 26. (For infants 0-6 months: Higher values, e.g., Lysine: 57 mg/g.)
Calculate the Digestible Amino Acid Score (DAAS) for Each IAA:
Example: If lysine DAAS is 1.60 but tryptophan is 0.90 (lowest), DIAAS = 0.90 (or 90%).
Express as Percentage (Optional): Multiply by 100 for % format, e.g., 90%.
For mixed proteins, calculate weighted averages based on each component's contribution.
Determine the Digestible Indispensable Amino Acid Content:
For each of the nine IAAs (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine—note: cysteine and tyrosine are considered with methionine and phenylalanine), calculate the digestible amount in mg per gram of protein.
- Formula: Digestible IAA (mg/g) = (Total IAA in test protein, mg/g) × (Ileal digestibility coefficient for that IAA, as a decimal; e.g., 0.95 for 95%).
- Digestibility is amino acid-specific and measured via ileal sampling (more precise than PDCAAS's fecal method).
Select the Reference Pattern: Use the FAO-recommended IAA requirements per gram of protein, adjusted for age groups (e.g., infants, children, adults).
For adults (the most common): Histidine: 10 mg/g, Isoleucine: 20, Leucine: 39, Lysine: 30, Methionine: 10.4 (or Methionine + Cystine: 15), Phenylalanine + Tyrosine: 25, Threonine: 15, Tryptophan: 4, Valine: 26. (For infants 0-6 months: Higher values, e.g., Lysine: 57 mg/g.)
Calculate the Digestible Amino Acid Score (DAAS) for Each IAA:
- For each IAA: DAAS = (Digestible IAA in 1g test protein, mg) / (IAA in reference pattern for 1g, mg).
- Example: For lysine in whey (48 mg digestible) vs. adult reference (30 mg): DAAS = 48 / 30 = 1.60 (or 160%).
Example: If lysine DAAS is 1.60 but tryptophan is 0.90 (lowest), DIAAS = 0.90 (or 90%).
Express as Percentage (Optional): Multiply by 100 for % format, e.g., 90%.
For mixed proteins, calculate weighted averages based on each component's contribution.
Where Both Metrics Quietly Stop Being Useful
Both PDCAAS and DIAAS treat protein as something eaten in isolation, under standardized conditions.
Real products are not eaten that way.
Real products are not eaten that way.
In supplements:
proteins are blended
sweeteners are present
fats and fibers modify digestion
surfactants alter interface behavior
matrix effects dominate perception
proteins are blended
sweeteners are present
fats and fibers modify digestion
surfactants alter interface behavior
matrix effects dominate perception
A protein with an excellent DIAAS score can:
taste unpleasant
foam excessively
feel thin or chalky
require heavy correction
taste unpleasant
foam excessively
feel thin or chalky
require heavy correction
Conversely, a blended protein system with a lower theoretical score can deliver:
better satiety
smoother digestion
higher compliance
more consistent daily intake
better satiety
smoother digestion
higher compliance
more consistent daily intake
From a CMO perspective, the best protein is the one people actually consume consistently.
Neither PDCAAS nor DIAAS measures that.
Neither PDCAAS nor DIAAS measures that.
The Hidden Problem: Scores Don’t Describe Systems
Quality metrics evaluate single proteins.
Manufacturers work with systems.
When proteins are blended — whey with casein, dairy with plant, collagen as a modifier — the amino acid profile, digestion kinetics, and functional behavior change. Scores are no longer additive in a simple way.
This is why chasing a single “high score” ingredient often produces worse products than designing a balanced system.
The metric rewards purity.
The product rewards balance.
Manufacturers work with systems.
When proteins are blended — whey with casein, dairy with plant, collagen as a modifier — the amino acid profile, digestion kinetics, and functional behavior change. Scores are no longer additive in a simple way.
This is why chasing a single “high score” ingredient often produces worse products than designing a balanced system.
The metric rewards purity.
The product rewards balance.
How CMOs Actually Use These Metrics
At BF-ESSE, PDCAAS and DIAAS are treated as boundary conditions, not goals.
They answer questions like:
Does this system meet nutritional adequacy requirements?
Are there limiting amino acids we must compensate for?
Will regulatory or market positioning require specific benchmarks?
They do not answer:
Will this product taste good?
Will it dissolve cleanly?
Will it feel satisfying?
Will consumers keep using it?
Those answers come from matrix design, not scores.
They answer questions like:
Does this system meet nutritional adequacy requirements?
Are there limiting amino acids we must compensate for?
Will regulatory or market positioning require specific benchmarks?
They do not answer:
Will this product taste good?
Will it dissolve cleanly?
Will it feel satisfying?
Will consumers keep using it?
Those answers come from matrix design, not scores.
How CMOs Actually Use These Metrics
At BF-ESSE, protein development does not start with flavors or claims.
It starts with questions like:
How should this product hydrate?
How should it move and disappear in the mouth?
How tolerant must it be to real-world use?
How much correction should be needed later?
Only after the protein matrix is defined do we add correction layers.
That is the difference between engineering and assembly.
It starts with questions like:
How should this product hydrate?
How should it move and disappear in the mouth?
How tolerant must it be to real-world use?
How much correction should be needed later?
Only after the protein matrix is defined do we add correction layers.
- When the matrix is right:
- fewer additives are needed
- mouthfeel feels natural
- flavors behave predictably
- scale-up becomes boring (in the best sense)
That is the difference between engineering and assembly.
The Practical Takeaway
PDCAAS and DIAAS are useful — but only if you know what problem you are solving.
If the goal is:
nutritional adequacy → metrics matter
regulatory alignment → metrics matter
clinical comparison → metrics matter
If the goal is:
a successful protein product
repeat consumption
stable manufacturing
scalable formulation
Then metrics are just the starting line.
Protein quality in formulation is not a number.
It is an experience shaped by structure, digestion dynamics, and system behavior.
If the goal is:
nutritional adequacy → metrics matter
regulatory alignment → metrics matter
clinical comparison → metrics matter
If the goal is:
a successful protein product
repeat consumption
stable manufacturing
scalable formulation
Then metrics are just the starting line.
Protein quality in formulation is not a number.
It is an experience shaped by structure, digestion dynamics, and system behavior.