If you've ever heard that plant protein is automatically "lower quality" than animal protein, potato and soy are two foods worth a closer look.
On modern protein-quality scales, both can perform remarkably well. In fact, potato protein can rank among the highest-quality plant proteins measured by DIAAS, while soy routinely scores as a high-quality protein source.
That may sound strange. Potatoes are usually thought of as a starchy carbohydrate, not a protein powerhouse. Soy, meanwhile, is sometimes dismissed as merely one more plant-based alternative to animal protein.
The reality is more interesting.
Protein quality isn't determined simply by how many grams of protein a food contains. It depends on the amino acids that protein provides, how well those amino acids are digested and absorbed, and whether the protein supplies enough of the essential amino acids the human body needs.
That's where DIAAS, or the Digestible Indispensable Amino Acid Score, becomes useful.
DIAAS helps explain why some plant proteins outperform expectations. It also reveals why the blanket statement that "plant protein is incomplete" is far too simplistic.
For people eating a vegan or plant-forward diet, this distinction matters. A food doesn't have to resemble meat, dairy, or eggs to provide high-quality protein.
And while potatoes themselves aren't especially protein-dense, the protein fraction extracted from potatoes has an unusually favorable amino acid profile.
What Is the Potato Protein Quality Score?
The potato protein quality score refers to how well potato protein performs when evaluated using measures such as DIAAS and PDCAAS.
Potato protein is notable because it contains all nine essential amino acids in meaningful amounts and has a relatively favorable balance of those amino acids.
Studies evaluating potato protein have reported DIAAS values around or above the 0.90 range, with some analyses placing potato protein above 1.00 depending on the reference pattern and methodology used.
That is unusually strong for a plant protein.
One important qualification: a DIAAS value belongs to a particular protein ingredient or food sample under a particular testing method. It isn't necessarily a permanent score for every potato, potato product, or potato protein powder.
Processing, variety, measurement technique, and the reference amino acid pattern can all influence the result.
Still, the broader finding is consistent: potato protein can have exceptionally high protein quality.
Does potato protein have a DIAAS above 100?
In some published analyses, yes.
When protein quality is evaluated against the amino acid requirements of young children, potato protein has been classified as an "excellent quality" protein with a DIAAS above 100.
That doesn't mean a potato provides more than 100% of your daily protein needs. It means the digestible essential amino acid content of the protein exceeds the selected reference pattern.
The distinction is important.
DIAAS is a protein quality measure, not a percentage of daily protein intake.
A food can have excellent protein quality while containing relatively little total protein.
That's exactly why potatoes make this topic so fascinating.
Why DIAAS Matters More Than Simply Counting Protein
Looking only at grams of protein tells you how much protein you're eating. It doesn't tell you how useful that protein is as a source of essential amino acids.
Imagine two foods each provide 20 grams of protein.
One might contain a well-balanced supply of essential amino acids and be highly digestible. The other could contain less of one essential amino acid, making that amino acid the limiting factor.
The two foods would not necessarily provide equivalent nutritional value.
DIAAS attempts to capture this difference.
What does DIAAS measure?
DIAAS measures the digestible amount of each indispensable, or essential, amino acid in a protein and compares it with human amino acid requirements.
The basic idea is:
- Identify the essential amino acids in a protein.
- Determine how much of those amino acids is digestible.
- Compare the digestible amino acid amounts with an age-specific reference pattern.
- Identify the lowest ratio.
- Use that lowest ratio as the DIAAS.
The lowest ratio is especially important because it identifies the limiting amino acid.
If a protein has plenty of every essential amino acid except one, that weaker amino acid can determine the overall score.
This is one reason different plant proteins perform so differently.
Why Plant Protein Quality Varies So Much
"Plant protein" isn't one nutritional category.
That's perhaps the biggest misconception surrounding vegan protein.
Rice protein, wheat protein, pea protein, soy protein, potato protein, oat protein, hemp protein, and other plant proteins have different amino acid profiles and different digestibility characteristics.
Their protein quality scores can therefore vary substantially.
Grains often have a lysine problem
Many cereal grains are relatively low in lysine compared with human amino acid requirements.
That makes lysine a common limiting amino acid for proteins from foods such as wheat, corn, and rice.
This doesn't make those foods unhealthy or nutritionally useless.
It simply means that, when the protein is evaluated by itself, its amino acid pattern may be less favorable than that of a protein such as soy or potato.
Legumes have a different limitation
Beans, peas, and other legumes tend to have strong lysine content but are comparatively less abundant in the sulfur-containing amino acids methionine and cysteine.
Again, that doesn't mean legumes are poor foods.
It means different plant proteins have different strengths and weaknesses.
This is precisely why eating a varied plant-based diet works so well nutritionally.
Potato protein is unusual
Potato protein doesn't fit neatly into the traditional grain-versus-legume comparison.
Its amino acid pattern is unusually favorable.
Potato protein provides substantial amounts of essential amino acids including lysine, leucine, isoleucine, valine, threonine, and tryptophan.
That combination helps explain its strong performance on protein quality scales.
Why Potato Protein Scores So Well
There are several reasons the potato protein quality score can be surprisingly high.
1. Potato protein contains all the essential amino acids
Humans require nine essential amino acids from the diet:
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
Potato protein contains all nine.
The important point isn't merely that they're present. Their relative amounts matter.
Potato protein has a particularly favorable balance of several essential amino acids that commonly limit other plant proteins.
2. Potato protein is rich in lysine
Lysine is one of the amino acids that can limit the quality of grain-based proteins.
Potato protein, by comparison, contains a relatively generous amount of lysine.
That helps explain why it can perform so differently from proteins derived from wheat or rice.
3. It supplies substantial branched-chain amino acids
Potato protein also provides the branched-chain amino acids leucine, isoleucine, and valine.
Leucine is especially well known for its role in stimulating muscle protein synthesis.
That doesn't make potato protein a magic muscle-building food. Muscle growth depends on total protein intake, energy intake, resistance training, recovery, and many other factors.
But its amino acid profile is one reason researchers find potato protein nutritionally interesting.
4. Digestibility matters
Amino acid content is only part of protein quality.
The body has to digest the protein and absorb its amino acids.
DIAAS incorporates digestibility at the level of individual indispensable amino acids, making it more informative than simply looking at the amino acid content of an undigested protein.
That distinction matters when comparing different plant proteins.
Potato Protein vs. Soy Protein: Which Is Better?
Both are among the more impressive plant proteins, but they aren't identical.
Soy protein is generally considered a high-quality plant protein, while potato protein can score exceptionally high in certain DIAAS analyses.
Soy has a long history of use as a major plant protein source. Soybeans, tofu, tempeh, soy milk, soy flour, soy concentrate, and soy isolate all provide protein, but their quality scores aren't necessarily identical.
The form and processing method matter.
Soy protein DIAAS score
Soy protein products have produced DIAAS values that commonly fall in the high-quality range, with many analyses around the mid-80s to low-90s.
Soy protein isolate often performs particularly well because processing removes much of the carbohydrate, fiber, and other components, leaving a concentrated protein ingredient.
The exact soy protein DIAAS score depends on the product and the study.
A useful way to think about it is that soy generally clears the bar for high-quality plant protein, even though its score may not always match the highest-scoring animal proteins or certain potato protein preparations.
Potato vs. soy protein
The comparison gets more interesting when you look beyond a single number.
| Protein | General protein-quality picture |
|---|---|
| Potato protein | Exceptionally high in some DIAAS analyses |
| Soy protein | Consistently high-quality plant protein |
| Pea protein | Moderate to high, depending on product |
| Wheat protein | Lower, largely because of lysine |
| Rice protein | Lower, with lysine often limiting |
| Many nuts and seeds | Variable, depending on amino acid profile and digestibility |
The important lesson isn't that potato "beats" soy or that soy "beats" every other plant.
The lesson is that plant protein quality exists on a spectrum.
Potato Protein Is Not the Same as Eating a Potato for Protein
Here's an important distinction that often gets lost in online discussions.
A potato can contain high-quality protein while still being a relatively low-protein food.
That's not contradictory.
Protein quality and protein quantity are different measurements.
A potato contains mostly water and carbohydrate, with protein making up a smaller portion of its total weight. Potato protein isolates and concentrates, on the other hand, are specifically manufactured to concentrate the protein fraction.
So when researchers report an impressive potato protein quality score, they're usually evaluating potato protein itself, often in a concentrated ingredient—not claiming that a baked potato is equivalent to a scoop of protein powder.
This distinction also explains why potato protein can be nutritionally interesting without turning the humble potato into a high-protein food.
How DIAAS Differs From PDCAAS
If you've researched protein quality before, you've probably encountered another acronym: PDCAAS.
That's the Protein Digestibility-Corrected Amino Acid Score.
PDCAAS has been widely used to evaluate protein quality, but it has limitations.
One major difference is that PDCAAS traditionally uses overall fecal nitrogen digestibility and caps scores at 1.00.
DIAAS instead focuses on the digestibility of individual indispensable amino acids, using ileal digestibility, and scores aren't capped at 1.00.
That means a DIAAS can exceed 100.
Why can a DIAAS score be greater than 100?
A score above 100 means the digestible indispensable amino acid content exceeds the amino acid requirement represented by the selected reference pattern.
It does not mean the food is "100% more nutritious."
It also doesn't mean that eating twice as much protein produces twice the benefit.
Think of DIAAS as a way to evaluate the quality and amino acid adequacy of a protein—not as a measure of overall healthfulness.
The Most Important Protein Quality Concept: The Limiting Amino Acid
One of the best ways to understand DIAAS is to imagine a barrel made from wooden planks.
The barrel can only hold water up to the height of its shortest plank.
Protein quality works somewhat similarly.
A protein might contain abundant leucine, valine, and lysine, but if one essential amino acid is relatively scarce, that amino acid can limit the score.
This is why simply saying "this food contains all nine essential amino acids" isn't enough.
The proportions matter.
Why combining plant proteins works
Different plant proteins have different limiting amino acids.
That creates an opportunity for protein complementarity.
For example, a grain-based protein that is relatively low in lysine can complement a legume protein that supplies more lysine.
Likewise, a high-quality protein such as soy or potato protein can contribute an amino acid pattern that helps improve the overall quality of a mixture.
You don't need to calculate amino acid ratios at every meal.
A varied diet generally accomplishes this naturally.
Does Being Vegan Mean You Get Lower-Quality Protein?
No.
A vegan diet can provide high-quality protein.
The misconception comes partly from treating all plant proteins as though they have the same amino acid profile.
They don't.
Soy and potato are two examples of plant proteins that challenge that assumption.
Other plant foods can contribute useful protein as well. Beans, lentils, peas, whole grains, nuts, seeds, and higher-protein plant products can all fit into a balanced diet.
The practical issue for someone eating entirely plant-based is less about finding one magical "perfect" protein and more about getting enough total protein from a varied selection of foods.
What Are the Best Quality Vegan Protein Sources?
If your goal is to prioritize protein quality on a vegan diet, soy and potato protein are especially interesting choices.
Other options include:
Soy foods
Tofu, tempeh, edamame, soy milk, textured soy protein, and soy protein isolate can all contribute substantial protein.
Soy is especially useful because it's available in both minimally processed foods and concentrated protein products.
Potato protein
Potato protein isolate is less familiar to consumers but has gained attention as a high-quality plant protein ingredient.
Its particularly favorable amino acid profile makes it one of the more interesting alternatives to conventional pea, rice, or wheat protein.
Pea protein
Pea protein can provide a substantial amount of protein and performs better than many people might assume.
Its amino acid profile is different from soy and potato, however, and its DIAAS can vary by product.
Beans and lentils
Whole legumes aren't necessarily as concentrated in protein as protein isolates, but they're valuable foods because they provide protein alongside fiber, carbohydrates, minerals, and other nutrients.
Whole grains and seeds
These contribute protein too, but they shouldn't necessarily be evaluated in isolation.
A diet containing multiple plant protein sources can provide a broad amino acid profile across the day.
How to Choose a High-Quality Plant Protein Powder
If you're buying a vegan protein powder, don't judge it solely by the number printed next to "protein."
Consider several factors.
Look at the protein source
Soy, potato, pea, and blends can all be useful.
A blend may combine proteins with complementary amino acid profiles.
Check the protein per serving
A protein powder can have an impressive amino acid profile but still provide relatively little protein per scoop.
Look at the actual grams of protein.
Consider the ingredient list
A shorter ingredient list isn't automatically better, but it can make it easier to understand what you're consuming.
Look for amino acid information when available
If a manufacturer provides an amino acid profile, pay attention to essential amino acids rather than focusing exclusively on total protein.
Leucine can be particularly relevant for people interested in muscle protein synthesis.
Don't confuse "complete protein" with "high-quality protein"
A complete protein contains all nine essential amino acids.
A high-quality protein also needs to provide them in useful amounts and in a form the body can digest and absorb efficiently.
Those concepts overlap, but they aren't identical.
Common Plant Protein Misconceptions
"Plant proteins are incomplete."
Some plant proteins have less of one or more essential amino acids than the reference pattern, but that doesn't make plant protein useless.
And some plant proteins, including soy, provide all nine essential amino acids in favorable amounts.
"You have to combine proteins at every meal."
Not necessarily.
The idea that every meal must contain a perfectly calculated complementary protein combination is an oversimplification.
Eating a varied diet over the course of the day provides multiple protein sources and amino acid profiles.
"Potatoes don't count as protein."
Potatoes are not high-protein foods, but the protein they contain has an interesting amino acid profile.
Those are two different statements.
"A DIAAS of 100 means the food is nutritionally perfect."
No.
DIAAS evaluates protein quality. It doesn't measure fiber, vitamins, minerals, fats, calories, phytochemicals, or the overall healthfulness of a food.
A protein-quality score is one piece of nutritional information.
"The highest protein-quality score automatically means the healthiest food."
Not at all.
A protein isolate and a whole food can have very different nutritional roles.
The best diet isn't simply the one containing foods with the highest DIAAS values. Overall dietary pattern matters.
Why This Matters for Plant-Based Athletes
Protein quality becomes especially interesting for people who train regularly.
Resistance exercise increases the importance of consuming sufficient protein and essential amino acids.
Plant-based athletes can meet protein needs, but they may benefit from paying attention to both total protein intake and the amino acid composition of their protein sources.
High-quality plant proteins such as soy and potato protein can make this easier.
That doesn't mean every vegan athlete needs a specialized potato protein supplement.
It means that plant-based eating doesn't require accepting inherently inferior protein.
A well-planned vegan diet can include concentrated, high-quality protein sources alongside whole foods.
How to Use This Information in Real Life
You don't need a spreadsheet of amino acid ratios to eat well.
Instead, use a few simple principles.
First, eat enough total protein.
Protein quality can't compensate for an inadequate overall protein intake.
Second, vary your sources.
Rotate among legumes, soy foods, grains, seeds, nuts, and other plant protein sources.
Third, include concentrated protein sources when useful.
Protein-rich tofu, tempeh, textured soy protein, or a plant protein powder can make it easier to reach higher protein targets.
Fourth, don't judge a food by reputation.
A food's category doesn't tell you everything about its protein quality.
Potato protein is a perfect example.
Finally, look at the whole diet.
Protein quality is important, but so are fiber, micronutrients, energy intake, food variety, and overall dietary pattern.
For people who want their lifestyle to reflect plant-based values beyond the dinner plate, brands such as The Dharma Store pair plant-based living with mindfulness and ethical lifestyle choices, including Vegan T-Shirts.
Is Potato Protein the Future of Vegan Protein?
It could become more prominent, particularly as food manufacturers look for plant proteins with strong nutritional characteristics.
Potato protein offers an unusual combination: a favorable essential amino acid profile, high protein quality in several analyses, and a source that doesn't depend on the traditional grain-or-legume protein categories.
But it's important not to turn an interesting scientific finding into another nutrition myth.
Potato protein isn't automatically superior to every other plant protein.
Its score varies by test conditions and reference population. Different products can have different nutritional characteristics. And a high-quality protein ingredient doesn't replace the benefits of eating whole plant foods.
What potato protein does provide is a useful counterexample to the idea that plant proteins are inherently low quality.
Why Protein Quality Is More Complicated Than "Animal vs. Plant"
The most useful takeaway from DIAAS isn't that one category of food wins.
It's that protein quality is a spectrum.
Some plant proteins have relatively low scores when evaluated alone. Others perform extremely well.
Soy is a strong example of a high-quality plant protein. Potato protein is an even more surprising example because the whole potato is rarely thought of as a meaningful protein source.
The difference comes down to amino acid composition and digestibility—not whether the protein originated in a plant.
That's an important shift in how to think about vegan nutrition.
Instead of asking, "Is plant protein lower quality?" a better question is:
Which plant proteins provide the essential amino acids I need, in useful amounts, and in a form my body can digest?
That question produces a much more accurate answer.
Potato Protein Quality Score: The Bottom Line
The potato protein quality score is surprisingly high because potato protein has a favorable essential amino acid profile and can provide highly digestible indispensable amino acids.
DIAAS research has identified potato protein as an unusually high-quality plant protein, with some analyses placing it above 100 under certain reference patterns. Soy protein also consistently performs well, generally landing in the high-quality range.
The broader lesson is even more useful.
Plant protein is not one thing.
Rice, wheat, pea, soy, potato, beans, and other plant proteins differ substantially in amino acid composition and digestibility. Some have limiting amino acids that lower their individual scores. Others, such as soy and potato protein, can score remarkably well.
For anyone following a vegan or plant-forward diet, that means there's no reason to think of protein quality as an automatic disadvantage.
Choose a variety of protein-rich plant foods, consume enough total protein, and remember that the nutritional value of a diet is determined by far more than a single score.
The humble potato, surprisingly, has a pretty good protein story after all.
Frequently Asked Questions
What is the potato protein quality score?
Potato protein has demonstrated a high DIAAS in research, with reported values around 0.94 to 1.00 or higher depending on the study, protein preparation, and reference amino acid pattern. Some analyses classify potato protein as an excellent-quality protein.
Is potato protein a complete protein?
Yes. Potato protein contains all nine essential amino acids. Its favorable balance of essential amino acids is one reason it performs unusually well on protein-quality assessments.
What is the soy protein DIAAS score?
Soy protein generally has a DIAAS in the high-quality range, with many analyses producing scores around the mid-80s to low-90s. Soy protein isolate can perform particularly well. The exact value varies with processing, product, testing method, and reference pattern.
Is potato protein better than pea protein?
Not necessarily in every situation. Potato protein can have a higher DIAAS than many pea protein preparations, but protein quality varies by product and measurement method. Both can be useful components of a plant-based diet.
What is the best quality vegan protein?
There isn't one universal winner, but soy and potato protein are among the most impressive plant proteins based on amino acid composition and DIAAS research. Pea protein, legumes, grains, nuts, and seeds can also contribute meaningfully to a balanced vegan diet.
Do vegans need to combine proteins at every meal?
No. Most people don't need to carefully combine complementary proteins at every meal. Eating a varied diet containing different plant protein sources throughout the day can provide a broad range of essential amino acids.
The information in this article is for educational purposes only and should not be considered medical advice. Always consult a qualified healthcare professional regarding dietary or health concerns.