What is PDCAAS and How is it Measured?
The Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method recommended by the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) to measure protein quality. The score is based on two key factors: the amino acid requirements for humans and the digestibility of the protein. It is calculated by comparing the food's essential amino acid content to a standard reference pattern and then correcting for how well the body can digest and absorb it.
The maximum possible score is 1.0, a perfect score which indicates that the protein provides 100% or more of all essential amino acids required per unit of protein after digestion. Any value higher than 1.0 is capped or 'truncated' to 1.0. The test was originally based on the needs of young children, and a PDCAAS of 1.0 signifies an excellent protein source.
Soy Protein Isolate: The Plant-Based Champion
Among all single-source plant proteins, soy protein isolate is the one that consistently achieves a PDCAAS of 1.0. Soy protein isolate is a highly refined form of soy protein, where the processing removes most carbohydrates and fats, leading to a protein content of over 90%. This refining process also improves its digestibility and reduces antinutritional factors, making the amino acids more available for the body to use. This complete amino acid profile, along with excellent digestibility, is what secures its top-tier PDCAAS score.
Other Complete Vegetarian Protein Sources
While soy protein isolate is the highest scorer, several other vegetarian foods are also considered 'complete' proteins, meaning they contain all nine essential amino acids. Their PDCAAS scores are often high, but may not reach the 1.0 cap, especially in their whole, unprocessed form.
- Quinoa: This ancient pseudocereal is a popular source of complete protein for vegetarians. A single cup of cooked quinoa provides a significant amount of protein and is also a great source of fiber, iron, and magnesium.
- Buckwheat: Another pseudocereal, buckwheat offers a complete amino acid profile, though it is slightly lower in protein than quinoa. It is an excellent source of manganese, phosphorus, and copper.
- Hemp Seeds: These small seeds are a fantastic source of complete protein and are rich in essential fatty acids. Just three tablespoons contain a substantial amount of protein and iron.
- Spirulina: This blue-green algae is a potent complete protein source and is also rich in antioxidants, B vitamins, and iron.
- Nutritional Yeast: Often used to add a cheesy flavor to dishes, nutritional yeast is a complete protein, particularly when fortified with vitamin B12.
- Ezekiel Bread: This bread is made from a combination of sprouted whole grains and legumes, including wheat, barley, beans, and lentils. The combination of these ingredients makes it a complete protein source.
The Power of Complementary Proteins
It's important to remember that achieving a PDCAAS of 1.0 isn't necessary with a single food if you have a varied diet. A balanced vegetarian diet can easily provide all essential amino acids by combining different plant protein sources throughout the day, a concept known as complementary proteins. The body stores essential amino acids and can combine them as needed. For example, grains like rice are typically low in lysine, while legumes like beans are rich in lysine but lower in methionine. Combining them, as in the classic beans and rice dish, creates a complete protein profile. This combination can also result in a combined PDCAAS of 1.0. Other classic examples include hummus with pita bread and peanut butter on whole wheat toast.
Comparison of Vegetarian Protein Sources
| Protein Source | PDCAAS Score | Completeness | Key Nutrients | Notes |
|---|---|---|---|---|
| Soy Protein Isolate | 1.00 | Complete | Protein, Iron, Calcium | Highly refined and bioavailable; often used in supplements. |
| Tofu/Tempeh | ~0.9-1.00 | Complete | Protein, Fiber, Calcium | Fermented and whole soy products with slightly lower scores than isolates. |
| Quinoa | Varies, high score | Complete | Fiber, Magnesium, Iron | Whole food pseudocereal; score depends on processing and type. |
| Pea Protein | 0.82-0.91 | Incomplete (low in SAA) | Iron, Fiber | Often blended with rice protein to increase PDCAAS. |
| Rice Protein | ~0.50 | Incomplete (low in Lysine) | Manganese, Phosphorus | Often blended with pea protein to create a complete profile. |
| Chickpeas | 0.78 | Incomplete | Fiber, Folate, Iron | Legume, can be paired with grains for a complete protein. |
The Shift to DIAAS: A More Accurate Measure
While PDCAAS is still widely used, a newer system, the Digestible Indispensable Amino Acid Score (DIAAS), is gaining traction. DIAAS is considered more accurate because it measures the digestibility of each individual essential amino acid at the end of the small intestine (ileum), rather than measuring total nitrogen digestibility in feces, which was a limitation of PDCAAS. Unlike PDCAAS, DIAAS does not cap scores at 1.0, allowing for a more accurate ranking of protein quality. However, the PDCAAS method remains the official standard in many countries, including the United States.
Conclusion: Prioritize Variety Over Perfection
The short answer to which vegetarian protein has PDCAAS 1 is soy protein isolate. Its refined and highly digestible nature earns it a perfect score, on par with high-quality animal proteins. However, a diverse and balanced vegetarian diet can effortlessly meet all essential amino acid needs without fixating on a single food's PDCAAS. Including a variety of legumes, whole grains, nuts, and seeds ensures a robust intake of all necessary amino acids. The discovery of soy protein's perfect score provides reassurance that vegetarians have access to excellent single-source proteins, but smart food combinations are equally effective and nutritious. For further information on obtaining a complete protein on a vegan or vegetarian diet, resources like Harvard's Nutrition Source can be helpful.
Why is Soy Protein Isolate the Only Vegetarian Protein with a PDCAAS of 1.0?
Soy protein isolate achieves a PDCAAS of 1.0 primarily because of its processing. The isolation process concentrates the protein to over 90%, removing antinutritional factors and making it highly digestible. It also contains all nine essential amino acids in the correct proportions, fulfilling the criteria for a perfect score.
Do other soy products like tofu and tempeh have a PDCAAS of 1.0?
While tofu and tempeh are complete proteins with high-quality amino acid profiles, their PDCAAS scores may be slightly lower than the isolate due to differences in processing and digestibility. However, their scores are still very high and they are considered excellent sources of protein for a vegetarian diet.
What is the difference between a complete protein and a PDCAAS of 1.0?
A complete protein contains all nine essential amino acids. A PDCAAS of 1.0 signifies that not only does the protein contain all essential amino acids, but it also does so in the correct proportions needed by the body and is highly digestible. All proteins with a PDCAAS of 1.0 are complete proteins, but not all complete proteins have a PDCAAS of 1.0.
Why was the PDCAAS score capped at 1.0?
The score was capped at 1.0 because anything higher was deemed to provide amino acids in excess of human requirements. The truncation of the score to 1.0 is a known limitation that the newer DIAAS system addresses.
Can a combination of incomplete proteins achieve a PDCAAS of 1.0?
Yes, absolutely. A blend of complementary proteins, such as pea protein (low in methionine) and rice protein (low in lysine), can create a combined amino acid profile that can achieve a PDCAAS of 1.0, or close to it. This is a fundamental concept in vegetarian nutrition.
Is it necessary to eat a PDCAAS 1.0 protein to be healthy as a vegetarian?
No. The PDCAAS score is a tool for comparing protein quality, but a varied and balanced vegetarian diet that includes a range of plant protein sources is more than sufficient to provide all essential amino acids. Consuming complementary proteins throughout the day is highly effective for meeting your needs.
Besides soy, what are some other notable complete vegetarian proteins?
In addition to soy, other noteworthy complete vegetarian protein sources include quinoa, buckwheat, hemp seeds, spirulina, and nutritional yeast. These can be easily incorporated into meals and snacks to boost your overall protein and nutrient intake.
Conclusion: Prioritize Variety Over Perfection
The short answer to which vegetarian protein has PDCAAS 1 is soy protein isolate. Its refined and highly digestible nature earns it a perfect score, on par with high-quality animal proteins. However, a diverse and balanced vegetarian diet can effortlessly meet all essential amino acid needs without fixating on a single food's PDCAAS. Including a variety of legumes, whole grains, nuts, and seeds ensures a robust intake of all necessary amino acids. The discovery of soy protein's perfect score provides reassurance that vegetarians have access to excellent single-source proteins, but smart food combinations are equally effective and nutritious. For further information on obtaining a complete protein on a vegan or vegetarian diet, resources like Harvard's Nutrition Source can be helpful.
Comparison of Vegetarian Protein Sources
| Protein Source | PDCAAS Score | Completeness | Key Nutrients | Notes |
|---|---|---|---|---|
| Soy Protein Isolate | 1.00 | Complete | Protein, Iron, Calcium | Highly refined and bioavailable; often used in supplements. |
| Tofu/Tempeh | High, close to 1.00 | Complete | Protein, Fiber, Calcium | Whole soy products, scores can be slightly lower than isolates. |
| Quinoa | Varies, high score | Complete | Fiber, Magnesium, Iron | Whole food pseudocereal; score depends on processing and type. |
| Pea Protein | 0.82-0.91 | Incomplete (low in SAA) | Iron, Fiber | Often blended with rice protein to increase PDCAAS. |
| Rice Protein | ~0.50 | Incomplete (low in Lysine) | Manganese, Phosphorus | Often blended with pea protein to create a complete profile. |
| Chickpeas | 0.78 | Incomplete | Fiber, Folate, Iron | Legume, can be paired with grains for a complete protein. |
The Power of Complementary Proteins
It's important to remember that achieving a PDCAAS of 1.0 isn't necessary with a single food if you have a varied diet. A balanced vegetarian diet can easily provide all essential amino acids by combining different plant protein sources throughout the day, a concept known as complementary proteins. The body stores essential amino acids and can combine them as needed. For example, grains like rice are typically low in lysine, while legumes like beans are rich in lysine but lower in methionine. Combining them, as in the classic beans and rice dish, creates a complete protein profile. This combination can also result in a combined PDCAAS of 1.0. Other classic examples include hummus with pita bread and peanut butter on whole wheat toast.
The Shift to DIAAS: A More Accurate Measure
While PDCAAS is still widely used, a newer system, the Digestible Indispensable Amino Acid Score (DIAAS), is gaining traction. DIAAS is considered more accurate because it measures the digestibility of each individual essential amino acid at the end of the small intestine (ileum), rather than measuring total nitrogen digestibility in feces, which was a limitation of PDCAAS. Unlike PDCAAS, DIAAS does not cap scores at 1.0, allowing for a more accurate ranking of protein quality. However, the PDCAAS method remains the official standard in many countries, including the United States.
Conclusion: Prioritize Variety Over Perfection
The short answer to which vegetarian protein has PDCAAS 1 is soy protein isolate. Its refined and highly digestible nature earns it a perfect score, on par with high-quality animal proteins. However, a diverse and balanced vegetarian diet can effortlessly meet all essential amino acid needs without fixating on a single food's PDCAAS. Including a variety of legumes, whole grains, nuts, and seeds ensures a robust intake of all necessary amino acids. The discovery of soy protein's perfect score provides reassurance that vegetarians have access to excellent single-source proteins, but smart food combinations are equally effective and nutritious. For further information on obtaining a complete protein on a vegan or vegetarian diet, resources like Harvard's Nutrition Source can be helpful.
