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potatoprotein.com

An independent research resource on potato protein isolate.

Reference

PDCAAS

**PDCAAS** (Protein Digestibility-Corrected Amino Acid Score) is a method for rating dietary protein quality, calculated by multiplying a protein's amino acid score by its fecal digestibility, with the result truncated at a maximum of 1.00.

How PDCAAS is calculated

The PDCAAS method compares the amino acid profile of a food protein against a standard reference requirement pattern. The lowest-scoring essential amino acid — the limiting amino acid — sets the amino acid score, which is then corrected for the protein’s fecal true digestibility. The product of those two figures is the PDCAAS. Any value above 1.00 is truncated to 1.00, so several high-quality proteins share the maximum score without distinction.

PDCAAS was developed in 1989 by a Joint FAO/WHO Expert Consultation on Protein Quality Evaluation (Nutrients, 2020, PMID:33266120) and was subsequently adopted as the FAO/WHO-recommended standard for evaluating protein quality. It remains the metric the FDA uses for protein content claims on food labels.

Reference scores

Animal proteins generally score higher than plant proteins. Under the established FAO/WHO values, milk, whey, egg, casein, and soy protein isolate all reach the maximum 1.00, while wheat gluten scores around 0.25. Among plant sources, four — canola, potato, pea, and quinoa — score at least 0.75 (Nutrients, 2020, PMID:33266120).

ProteinPDCAAS
Egg, milk, whey, casein, soy isolate1.00
Potato protein isolate0.92–1.00
Wheat gluten~0.25

Potato protein isolate’s range of 0.92–1.00 places it on par with several animal proteins and among the highest of any vegetable protein source. For a broader comparison of how scores translate into product selection, see the complete protein powder buyer’s guide.

Limitations and the shift to DIAAS

PDCAAS has two recognized shortcomings: it uses fecal rather than ileal digestibility, and its truncation at 1.00 hides real differences between proteins that exceed the reference pattern. Because of this, two proteins with an identical PDCAAS of 1.00 can stimulate muscle protein synthesis differently. In March 2013, the FAO proposed the Digestible Indispensable Amino Acid Score (DIAAS) as a replacement; DIAAS uses ileal digestibility and does not truncate, so values can exceed 100%. For unprocessed soya, the two methods diverge — a DIAAS of 86% versus a PDCAAS of 92%.