Understanding the PDCAAS
The Protein Digestibility-Corrected Amino Acid Score (PDCAAS) was the standard for measuring protein quality for many years, established by the FAO/WHO in 1991. The score ranges from 0 to 1.0, with 1.0 being the highest possible rank. The PDCAAS calculation is based on the amino acid profile of a food and its true fecal digestibility. Animal proteins generally have a higher PDCAAS than plant-based proteins. However, certain plant proteins, especially processed isolates, can achieve a top score. Although largely superseded by the Digestible Indispensable Amino Acid Score (DIAAS) due to limitations, PDCAAS remains widely used, particularly in the US.
Animal-Based Foods with the Highest PDCAAS
Many animal products are complete proteins and achieve the maximum PDCAAS of 1.0.
Eggs
Often called the "gold standard," whole eggs and egg whites have a perfect PDCAAS of 1.0.
Milk and Dairy Products
Dairy proteins like casein, whey, and milk protein concentrate also have a PDCAAS of 1.0. Whey is fast-absorbing, while casein is slow-digesting. Cottage cheese and Greek yogurt are other high-PDCAAS dairy options.
Meat and Fish
Meats and fish are very high-quality protein sources. Chicken and turkey breast often score close to 1.0. Lean beef, pork, and fish like salmon and tuna typically have scores above 0.90.
Plant-Based Foods with a High PDCAAS
Vegans and vegetarians have options to achieve high protein quality.
Soy Protein Isolate
Soy protein isolate is one of the few plant proteins with a perfect PDCAAS of 1.0.
Tofu and Edamame
Whole soybean products like tofu (around 0.90) and edamame (around 0.91) have very high PDCAAS scores.
Complementary Proteins
Combining plant foods can create a complete protein source with a high PDCAAS by pairing sources where one is high in an amino acid the other lacks. Examples include rice and beans, and hummus and pita bread.
PDCAAS Scores Comparison Table
| Food Item | PDCAAS Score | Limiting Amino Acid (if any) |
|---|---|---|
| Egg | 1.00 | None |
| Cow's Milk (Casein/Whey) | 1.00 | None |
| Soy Protein Isolate | 1.00 | None |
| Chicken Breast | ~1.00 | Tryptophan |
| Lean Beef | ~0.92 | - |
| Tofu | ~0.90 | Methionine+Cysteine |
| Edamame | ~0.91 | Methionine+Cysteine |
| Chickpeas | ~0.78 | Methionine+Cysteine |
| Rice + Beans | 1.00 | None |
List of High-Scoring PDCAAS Foods
- Eggs (Whole or Whites)
- Milk, Whey, and Casein Proteins
- Soy Protein Isolate
- Chicken and Turkey
- Lean Beef and Pork
- Fish (Salmon, Tuna, Shrimp)
- Cottage Cheese and Greek Yogurt
- Tofu and Edamame
- Combinations like Rice and Beans
The Shift to DIAAS
PDCAAS has limitations, such as truncating scores at 1.0 and using less accurate fecal digestibility data. The FAO proposed DIAAS in 2013 as a replacement. DIAAS uses ileal digestibility and offers untruncated scores for a more accurate measure. While DIAAS is more refined, PDCAAS is still widely used and relevant. For more details on the evolution of protein measurement, you can explore the comparative research published on NCBI.
Conclusion
Understanding what foods have the highest PDCAAS is valuable for optimizing protein intake. Foods with a PDCAAS of 1.0, including eggs, dairy proteins, and soy protein isolate, are the most complete and bioavailable sources. High-quality proteins are essential for functions like muscle repair, immune health, and growth. The PDCAAS serves as a useful benchmark, even with the newer DIAAS standard. Incorporating a variety of high-scoring animal and plant-based foods can help ensure a well-rounded diet that meets your nutritional needs.
