Potato protein quality is high by both of the metrics that actually decide the question: potato protein isolate carries a PDCAAS of 0.92–1.00 and a DIAAS reported as high as 100%. That places it alongside several animal proteins rather than below them, which is unusual for a plant source. Most plant proteins score lower than animal proteins, so potato is the exception worth understanding in detail.
This matters because protein quality is not one thing. It is a composite of two questions — does the protein contain the right amino acids in the right proportions, and can your body digest and absorb them — and the scoring systems answer those questions differently.
Is Potato Protein High Quality?
Yes. Potato protein isolate is high quality, scoring 0.92–1.00 on PDCAAS and up to 100% on DIAAS, comparable to egg, whey, and soy. A 2021 review in Food Research International describes potato protein as an emerging source of high-quality and allergy-free protein, and the PDCAAS for potato protein is among the highest of any vegetable protein source.
The general rule, restated across the literature, is that animal proteins score higher than plant proteins because they tend to be amino-acid complete and highly digestible. A 2024 review in Foods notes that animal proteins are generally highly digestible and nutritionally superior to plant proteins, with higher amino acid bioavailability (Foods, 2024). Potato protein is the case that complicates the rule: its amino acid profile and digestibility are complete enough to reach animal-protein territory. If you want the broader context on how the isolate is made and what it is, our pillar guide to what potato protein is covers the extraction and composition.
What Is PDCAAS, and What Does Potato Protein Score?
PDCAAS evaluates protein quality by comparing a food’s amino acid profile against a human reference requirement pattern, then correcting for digestibility. The maximum is 1.00, and any value above that is truncated down to 1.00. Potato protein isolate scores 0.92–1.00, among the highest of any plant source.
The Protein Digestibility Corrected Amino Acid Score was developed in 1989 by a Joint FAO/WHO Expert Consultation and adopted as the FAO/WHO recommended method for evaluating protein quality. The method works by identifying the “limiting” amino acid — the essential amino acid present in the smallest proportion relative to need — and using it to anchor the score, then multiplying by a digestibility factor.
The truncation rule is the key quirk. Several proteins — milk, whey, egg, casein, and soy protein isolate — all score 1.00, the highest possible value. Wheat gluten, limited in lysine, scores much lower, around 0.25. Because truncation flattens everything above 1.00, PDCAAS cannot distinguish a “just barely complete” protein from one with amino acids to spare. That limitation is precisely what the newer score was designed to fix.
| Protein source | PDCAAS | Notes |
|---|---|---|
| Whey protein isolate | 1.00 | Truncated; high leucine |
| Egg | 1.00 | Reference-grade animal protein |
| Casein | 1.00 | Slow-digesting |
| Soy protein isolate | 1.00 | Highest-scoring common legume |
| Potato protein isolate | 0.92–1.00 | Highest among vegetable sources |
| Pea protein | ≥0.75 | Limited in methionine |
| Wheat gluten | ~0.25 | Limited in lysine |
Source: PDCAAS method and truncation rule from Schaafsma G., Journal of Nutrition (2000, PMID 10867064); plant-protein figures from Nutrients (2020, PMID 33266120). Animal-protein 1.00 scores and potato protein PDCAAS 0.92–1.00 per published isolate data.
Among vegetable proteins, four — canola, potato, pea, and quinoa — reach a PDCAAS of at least 0.75 (Nutrients, 2020). Potato sits at the top of that group, closer to the animal proteins than to the plant average. For a fuller breakdown of how the scoring math works, see our explainer on DIAAS vs PDCAAS.
What Is DIAAS, and Why Did It Replace PDCAAS?
DIAAS, the Digestible Indispensable Amino Acid Score, was proposed by the FAO in March 2013 to replace PDCAAS as the protein quality standard. Its main improvement is that it does not truncate scores, so a protein with surplus amino acids can register above 100%. Potato protein isolate has a DIAAS reported as high as 100% (Food Science & Nutrition, 2020).
There are two substantive differences between the scores. First, DIAAS measures true ileal digestibility of each individual amino acid rather than crude fecal digestibility of total protein, which is a more accurate read of what actually reaches the bloodstream. Second, because DIAAS does not cap at 100%, it can rank high-quality proteins against one another instead of bundling them all at the ceiling.
Those changes produce practically meaningful gaps. For unprocessed soy products, DIAAS is 86% versus a PDCAAS of 92% — the same protein, two different verdicts (Frontiers in Nutrition, 2024). A 2024 analysis in Frontiers in Nutrition catalogues several such differences, which is why regulators have moved toward DIAAS as the preferred metric.
A note on convention, because it trips up most comparison articles: DIAAS is always expressed as a percentage. Potato protein’s DIAAS is “100%,” not “100.” Soy and potato protein isolates both reach a DIAAS of at least 100% for children and adults, making them comparable in quality to whey isolate, whose DIAAS runs 94%–100%. Writing one protein’s score as a decimal and another’s as a whole number invites a false comparison.
The Amino Acid and Leucine Profile
Potato protein’s quality scores rest on a complete amino acid profile: it contains all nine essential amino acids in proportions close to human requirements, with a protein content of 80–95% on a dry basis. Its main protein fraction is patatin, a well-characterized storage protein.
Leucine is the amino acid that warrants the closest look, because it is the primary trigger for muscle protein synthesis. Plant-based proteins often contain lower amounts of leucine and other essential amino acids than animal proteins, which can make them less effective at acutely stimulating synthesis (Current Developments in Nutrition, 2024). Whey, by contrast, is rapidly digested and leucine-rich, which is part of why it stimulated muscle protein accretion more effectively than slower proteins in older men (American Journal of Clinical Nutrition, 2011).
The practical takeaway is not that potato is inadequate — it clearly meets requirements — but that hitting a leucine threshold may take a slightly larger serving than it would with whey. If you are tracking that threshold, our guide on how much leucine per day to build muscle walks through the numbers, and our potato protein vs whey comparison covers the trade-offs side by side.
The Muscle Protein Synthesis Evidence
Scores predict quality; human trials confirm it. Two independent research groups, using different study designs, both found that potato protein isolate stimulates muscle protein synthesis — the clearest functional evidence that its high scores translate into a real anabolic response.
The first is the 2020 McMaster University trial led by Stuart Phillips (Oikawa et al.), published in Nutrients. In young women, 25g of potato protein isolate consumed twice daily stimulated muscle protein synthesis rates at rest and during exercise recovery. The women who consumed the additional potato protein raised their synthesis rate; the placebo group did not. This is meaningful because it tested a plant protein at a realistic dose and still produced a measurable result.
The second is a separate 2022 study from the Maastricht University group, “Potato protein ingestion increases muscle protein synthesis rates at rest and during recovery from exercise in humans,” published in Medicine & Science in Sports & Exercise. This was an original human trial — not a review, and not a continuation of the McMaster work — conducted by a different team. It reached the same conclusion: potato protein ingestion increased muscle protein synthesis at rest and during exercise recovery.
Two independent groups, at two universities, with different participants, converging on the same finding is stronger evidence than either study alone. It is the difference between a single positive result and a reproducible one. While plant proteins are often described as generally weaker for muscle protein synthesis, potato protein keeps turning up as an exception to that rule. For more on applying this to training, see our guide to protein for athletes.
Limitations and What the Scores Don’t Tell You
Two proteins with identical PDCAAS values can still differ in how they behave in the body. Soy protein isolate and whey both score 1.00 on PDCAAS, yet they differentially stimulate muscle protein synthesis — a reminder that a single number compresses a lot of biology (Nutrients, 2020).
The scores also say nothing about digestion speed, satiety, or hormonal response. In one comparative study, whey protein stimulated a greater GLP-1 response than potato protein, a difference linked to amino acid profile, specifically lower glutamine in potato (Nutrients, 2021). None of that shows up in a PDCAAS or DIAAS figure.
A few practical caveats round out the picture. Published DIAAS values come from specific commercial isolates, so a given product may vary with its processing. Potato protein is allergen-free relative to dairy, egg, soy, and nuts — but it is not allergen-free for someone with a true potato allergy, since the patatin allergen remains present. And quality scores describe a protein in isolation, not your whole diet: total daily intake and protein distribution across meals usually matter more than squeezing out the last few points of any single score. For the wider context on whether the isolate suits your needs, see is potato protein good for you.
The honest summary: potato protein isolate is a genuinely high-quality protein by both the older and the newer scoring systems, backed by two independent human trials. Whey retains a modest edge in leucine density and digestion speed. For anyone avoiding dairy, eggs, soy, or nuts, potato closes most of that gap on quality while removing the common allergens entirely.
