Digestible Indispensable Amino Acid Score
Digestible Indispensable Amino Acid Score is a protein quality method proposed in March 2013 by the Food and Agriculture Organization to replace the current protein ranking standard, the Protein Digestibility Corrected [Amino Acid Score].
The DIAAS accounts for amino acid digestibility at the end of the small intestine, providing a more accurate measure of the amounts of amino acids absorbed by the body and the protein's contribution to human amino acid and nitrogen requirements. This is in contrast to the PDCAAS, which is based on an estimate of total protein digestibility over the total digestive tract. Values stated using PDCAAS generally overestimate the amount of amino acids absorbed.
Calculation
As noted before, DIAAS considers the digestibility of individual essential amino acids. The amounts of each amino acid in the test food and in the digested mixture at the end of the small intestine is subtracted to give the absorbed amount of each EAA. The value is divided by the total amount of protein in the test food to give the milligrams of each EAA absorbed for each gram of the protein. One then looks up the desired reference pattern, which gives the amount of an EAA in 1 gram of the "reference protein". For each EAA, the "reference ratio" is calculated. The final DIAAS is 100% times the lowest reference ratio.Amino acid digestibility is preferably scored using humans. If humans are not available, determination in growing pigs or growing rats are acceptable. For measurement in humans, a minimally invasive dual-tracer method has been developed for the DIAAS method.
Example values
The table shows the ratings of selected foods comparing PDCAAS to DIAAS. The quality of various sources of protein depends on how it is processed, refined, stored, or cooked. . A major difference between DIAAS and PDCAAS, is that PDCAAS is truncated at 100%, while DIAAS is not. Multiple protein sources can also be combined to increase DIAAS, which can be effective at raising the max DIAAS of plant-based diets.When attempting to read the results the score refers to how much of each required protein is available to absorb in reference to how much is required per day.
| Food | PDCAAS | DIAAS for 0.5-3 yo | Limiting AA |
| Milk Protein Concentrate | 1.00 | 1.18 | Met + Cys |
| Whey Protein Isolate | 1.00 | 1.09 | Val |
| Soy Protein Isolate | 0.98 | 0.898 | Met + Cys |
| Pea Protein Concentrate | 0.893 | 0.822 | Met + Cys |
| Rice Protein Concentrate | 0.419 | 0.371 | Lys |
| Whole milk powder | 1.000 | 1.159 | |
| Tilapia | 1.00 | ||
| Tuna | 1.00 | ||
| Chicken breast | 1.00 | 1.08 | Trp |
| Pork | 1.17 | ||
| Beef | 1.000 | 1.116 | |
| Whole milk | 1.00 | 1.14 | Met + Cys |
| Egg | 1.00 | 1.13 | His |
| Egg | 1.01 | ||
| Chickpeas | 0.74 | 0.83 | Met + Cys |
| Tofu | 0.70 | 0.97 | Met + Cys |
| Peas | 0.782 | 0.647 | |
| Cooked peas | 0.597 | 0.579 | Met + Cys |
| Soybean | 1.000 | 0.996 | |
| Soy | 0.91 | Met + Cys | |
| Soya Flour | 1.00 | 1.05 | |
| Fava Bean | 0.55 | Met + Cys | |
| Cooked kidney beans | 0.648 | 0.588 | |
| Roasted peanuts | 0.509 | 0.434 | |
| Almonds | 0.39 | 0.40 | Lys |
| Wheat | 0.463 | 0.40-0.48 | |
| Wheat flour | 0.40 | ||
| Wheat bran | 0.53-0.60 | 0.41-0.49 | |
| Barley | 0.591 | 0.472 | |
| Rye | 0.553 | 0.476 | |
| Triticale | 0.553 | 0.498 | |
| Corn | 0.37 | 0.36 | Met + Cys |
| Corn Grain | 0.473 | 0.424 | |
| Corn-based cereal | 0.078 | 0.012 | Lys |
| Rice | 0.47 | Lys | |
| Cooked rice | 0.616 | 0.595 | Lys |
| Oats | 0.57 | Lys | |
| Cooked rolled oats | 0.670 | 0.542 | |
| Potato | 0.99 | 1.00 | |
| Quinoa | 0.677 | ||
| Quinoa flour | 0.79 | ||
| Gelatin | 0.02 | Trp | |
| Wheat/potato | 1.00 | ||
| Vegetables | 0.73-0.89 | ||
| Tubercles | 0.74-0.89 | ||
| Fresh Fruits | 0.64-0.76 | ||
| Dried Fruits | 0.48-0.66 | ||
| Legumes | 0.70-0.89 |
Comparing DIAAS to PDCAAS
- The PDCAAS uses the faecal digestibility while the DIAAS considers the ileal digestibility.
- The PDCAAS is truncated at 100% while DIAAS is not
- The PDCAAS experimentation protocol that determines the digestibility involves rats while the DIAAS advises to use pigs preferably as the pig digestive system is closer to the human's system.
- The PDCAAS considers the global digestibility of the product's protein while the DIAAS accounts for a specific digestibility percentage for each indispensable amino acid
- The reference values for the PDCAAS are based on a unique age group, the 2 to 5-year-old child which is deemed to be the more demanding. The DIAAS provides values for three different age groups, with more up to date data about human needs.