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PDCAAS – Protein Quality Score Explained

PDCAAS is a method for evaluating protein quality based on amino acid composition and digestibility. It is recognized as an international standard in nutrition science.

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Things worth knowing about "PDCAAS"

PDCAAS is a method for evaluating protein quality based on amino acid composition and digestibility. It is recognized as an international standard in nutrition science.

What is PDCAAS?

The PDCAAS (Protein Digestibility Corrected Amino Acid Score) is a scientific method used to assess the quality of dietary proteins. It measures how well a food protein can meet human amino acid requirements, taking into account both the amino acid profile and the digestibility of the protein. The PDCAAS was recommended in 1993 by the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) as the preferred method for evaluating protein quality in human nutrition.

How is PDCAAS Calculated?

The PDCAAS value is calculated using the following formula:

PDCAAS = (Amino Acid Score) × (True Fecal Digestibility)

Amino Acid Score: The ratio of the most limiting essential amino acid in the test protein compared to a reference value based on human requirements (typically derived from the needs of preschool children).
True Fecal Digestibility: The proportion of protein that is actually absorbed in the gut, typically measured through animal studies or in vitro methods.

The maximum PDCAAS value is capped at 1.0 (or 100%). Proteins scoring 1.0 are considered to fully meet human essential amino acid requirements.

PDCAAS Values of Common Foods

Different foods show different PDCAAS values:

Whey protein: 1.0 – among the highest of all dietary proteins.
Egg white: 1.0 – considered a reference protein in nutrition science.
Casein (milk protein): 1.0
Soybeans: 0.91–1.0 – highest value among plant-based proteins.
Beef: 0.92
Wheat: 0.42 – limiting amino acid is lysine.
Lentils: 0.52
Peanut butter: 0.52

Nutritional Relevance

The PDCAAS is especially important for:

Vegan and vegetarian diets: Since many plant-based proteins have lower PDCAAS values, combining different protein sources is recommended to cover all essential amino acids.
Athletes and muscle building: High-quality proteins with a PDCAAS of 1.0 are particularly effective at supporting muscle protein synthesis.
Children and vulnerable populations: The PDCAAS reference value is based on the amino acid requirements of preschool children, as they have the highest need for essential amino acids relative to body weight.
Food labeling and regulation: In some countries, the PDCAAS is used in the official evaluation of protein products and dietary supplements.

Limitations of PDCAAS

Despite its widespread use, the PDCAAS has several methodological limitations:

The score is capped at 1.0, which means differences between high-quality proteins (e.g., whey vs. egg) are not visible.
Fecal digestibility is typically measured in rats, which does not always translate precisely to human digestion.
Antinutritional factors (e.g., phytic acid, tannins in plant-based foods) can reduce actual protein utilization but are not fully captured in the PDCAAS model.
The method does not account for the specific site of digestion and absorption within the gastrointestinal tract.

PDCAAS vs. DIAAS

As an advancement over PDCAAS, the FAO and WHO have recommended since 2013 the use of DIAAS (Digestible Indispensable Amino Acid Score) as a more precise method. DIAAS measures the digestibility of each individual amino acid in the small intestine (not the large intestine) and is not capped at 1.0. Nevertheless, PDCAAS remains widely used in practice, in the food industry, and in scientific literature due to its relative simplicity.

References

FAO/WHO: Protein Quality Evaluation. Report of the Joint FAO/WHO Expert Consultation. FAO Food and Nutrition Paper 51, Rome 1991.
Schaafsma, G.: The Protein Digestibility-Corrected Amino Acid Score. Journal of Nutrition, 2000; 130(7): 1865S–1867S.
FAO: Dietary Protein Quality Evaluation in Human Nutrition. FAO Food and Nutrition Paper 92, Rome 2013.

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