Amino acid score

Amino Acids

Amino acid score, in combination with protein digestibility, is used to determine if a protein is complete. It compares the proportion of essential amino acids found in one protein to the proportion in a "reference protein" considered to be complete.

Methods of amino acid score calculation

PDCAAS and DIAAS are the two major protein standards which determine the completeness of proteins by their unique composition of essential amino acids. ^[1]

Simple AAS, PDCAAS

PDCAAS considers digestibility and AAS separately. It has a single "reference protein" profile, in which the amounts in milligrams of each essential amino acid (EAA) in each gram of the reference protein is listed. To find the AAS given the amino acid profile of the test protein T_i and the amino acid profile of the reference protein R_i: ^[2]

• For each essential amino acid i, calculate ⁠T_i/R_i⁠.
• Take the amino acid with the smallest value of ⁠T_i/R_i⁠. Call it l. This is the limiting amino acid.
• The AAS is 100% ×⁠T_l/R_l⁠.

PDCAAS estimates digestibility in a separate procedure. The estimated PD is multiplied with AAS to get PDCAAS. ^[2]

Digestibility-corrected AAS, DIAAS

DIAAS considers the profile of the essential amino acids that are actually absorbed. This value is calculated by estimating the amount of each EAA absorbed in the "test protein" by comparing how much of each EAA went into the mouth and how much was pumped out of the end of the small intestines. This was then turned into a profile A_i by dividing the amounts in milligrams of each EAA with the grams of the test protein eaten. From then on, the calculation is similar:

• For each essential amino acid i, calculate ⁠A_i/R_i⁠.
• Take the amino acid with the smallest value of ⁠A_i/R_i⁠. Call it l. This is the limiting amino acid taking actual absorption into account.
• The DIAAS is 100% ×⁠A_l/R_l⁠.

DIAAS provides three separate R_i reference profiles for different human age groups. ^[1]

References

1. Leser, S. (December 2013). "The 2013 FAO report on dietary protein quality evaluation in human nutrition: Recommendations and implications: FAO dietary protein report" (PDF). Nutrition Bulletin. 38 (4): 421–428. doi:10.1111/nbu.12063.
2. Gilani, G. Sarwar; Sepehr, Estatira (January 2003). "Protein Digestibility and Quality in Products Containing Antinutritional Factors Are Adversely Affected by Old Age in Rats". The Journal of Nutrition. 133 (1): 220–225. doi: 10.1093/jn/133.1.220 .