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Potato Protein vs Soy
**Potato Protein vs Soy** is a comparison of two plant-based protein isolates that differ in allergenicity and processing while both reaching high protein-quality scores. Soy is one of the major recognized food allergens; potato protein is not.
Completeness and protein quality
Both are complete proteins by amino-acid scoring. Under the Protein Digestibility-Corrected Amino Acid Score (PDCAAS), values above 100% are truncated to a maximum of 100% (a score of 1.00), so a high-quality protein like soy isolate reaches that ceiling (The Journal of Nutrition, Schaafsma, 2000, PMID:10867064). Potato protein isolate also scores at the high end and contains all nine essential amino acids. On the newer Digestible Indispensable Amino Acid Score (DIAAS), potato protein is classified as an excellent-quality protein with an average above 100%, while soy is classified as a high-quality protein with an average DIAAS of about 90% (Food Science & Nutrition, Herreman et al., 2020, PMID:33133540).
Equal PDCAAS values do not guarantee equal effects on muscle. Soy and whey can differentially stimulate muscle protein synthesis despite sharing the same PDCAAS, and whey stimulated greater post-exercise mixed muscle protein synthesis than soy or casein, attributed to faster digestion kinetics and higher leucine content (Journal of Applied Physiology, 2009, PMID:19589961).
Allergenicity
This is the clearest practical difference. Soy is among the major food allergens that regulators require to be declared on labels. Potato allergy is uncommon, and potato protein is frequently described as an allergy-free protein source. For a household avoiding dairy, eggs, nuts, and soy, potato protein sidesteps soy entirely.
The caveat: potato protein is not allergen-free in an absolute sense. Patatin and a 53 kDa protein have been identified as the main potato allergens (Molecular Immunology, 2018, PMID:30031281), and the Center for Research on Ingredient Safety at Michigan State University notes that anyone with a potato allergy should not consume potato protein, since the allergen is still present.
Processing
Potato protein is extracted from potato fruit juice and potato fruit water, a byproduct of potato starch production (Food and Bioprocess Technology, 2012). Commercial isolates contain roughly 80–95% protein on a dry basis. Soy isolate is produced from defatted soy through separate steps.
Purification also affects digestive tolerance. Monash University notes that plant-derived proteins such as soy and pea can be particularly challenging to purify and often retain some FODMAPs such as GOS and fructan, which can trigger symptoms in people with IBS. For a broader framework on weighing completeness, allergens, and additives across sources, see our guide to choosing a protein powder.
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