Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS)


Br J Nutr. 2017 Mathai JK et al. Feb;117(4):490-499. doi: 10.1017/S0007114517000125   Link to paper


“An experiment was conducted to compare values for digestible indispensable amino acid scores (DIAAS) for four animal proteins and four plant proteins with values calculated as recommended for protein digestibility-corrected amino acid scores (PDCAAS) but determined in pigs instead of in rats. Values for standardised total tract digestibility (STTD) of crude protein (CP) and standardised ileal digestibility (SID) of amino acids (AA) were calculated for whey protein isolate (WPI), whey protein concentrate (WPC), milk protein concentrate (MPC), skimmed milk powder (SMP), pea protein concentrate (PPC), soya protein isolate (SPI), soya flour and whole-grain wheat. The PDCAAS-like values were calculated using the STTD of CP to estimate AA digestibility and values for DIAAS were calculated from values for SID of AA. Results indicated that values for SID of most indispensable AA in WPI, WPC and MPC were greater (P<0·05) than for SMP, PPC, SPI, soya flour and wheat. With the exception of arginine and tryptophan, the SID of all indispensable AA in SPI was greater (P<0·05) than in soya flour, and with the exception of threonine, the SID of all indispensable AA in wheat was less (P<0·05) than in all other ingredients. If the same scoring pattern for children between 6 and 36 months was used to calculate PDCAAS-like values and DIAAS, PDCAAS-like values were greater (P<0·05) than DIAAS values for SMP, PPC, SPI, soya flour and wheat indicating that PDCAAS-like values estimated in pigs may overestimate the quality of these proteins.”


Protein digestibility-corrected amino acid scores and digestible indispensable amino acid scores differentially describe protein quality in growing male rats.


Rutherfurd SM et al. J Nutr. 2015 Feb; 145(2):372-9. doi: 10.3945/jn.114.195438.   Link to paper



The FAO has recommended replacing the protein digestibility-corrected amino acid score (PDCAAS) with the digestible indispensable amino acid score (DIAAS). 

The objective of this study was to compare aspects underlying the calculation of the DIAAS and PDCAAS, including 1) fecal digestibility vs. ileal digestibility, 2) using a single nitrogen digestibility value for all amino acids, and 3) the effect of truncation. Truncated PDCAAS and untruncated DIAAS values calculated as formally defined were also compared and DIAAS data presented for 14 dietary protein sources.



Semisynthetic wheat starch-based diets were formulated to contain the test protein (as consumed by humans) source (whey- and soy-protein isolates, milk-, whey-, rice- and pea- protein concentrates, cooked kidney beans, roasted peanuts, cooked peas, corn-based breakfast cereal, cooked rice, cooked rolled oats, and wheat bran) as the sole nitrogen source and with an indigestible marker (titanium dioxide). Growing male rats (250 g bodyweight) were given a basal casein-based diet from day 1 to day 7 and then allocated (n = 6) to the test diets for day 8 to day 14 before ileal digesta were collected after the rats were killed. Total feces were collected from day 11 to day 14.



True fecal nitrogen digestibility was different (P < 0.05; 10% difference on average) from true ileal nitrogen digestibility for 11 of the 14 protein sources. True ileal nitrogen digestibility was different (P < 0.05) from true ileal amino acid digestibility for almost half of the indispensable and conditionally indispensable amino acids (differences ranged from 0.9% to 400%). DIAAS values ranged from 0.01 for a corn-based cereal to 1.18 for milk protein concentrate.



Untruncated PDCAAS values were generally higher than a DIAAS values, especially for the poorer quality proteins; therefore, the reported differences in the scores are of potential practical importance for populations in which dietary protein intake may be marginal.”


Dietary protein quality evaluation in human nutrition, Report of an FAO Expert Consultation


FAO, Publication; 2013 (ISBN:9789251074176)  Link to publication



“Protein is supplied by food ingredients, whole foods, sole-source foods and mixed diets and the match between dietary supply and human protein needs is vital to support the health and well-being of human populations. Since 1989 the Protein Digestibility Corrected Amino Acid Score (PDCAAS) method for evaluating protein quality has been used widely. However, limitations of PDCAAS have been recognised and new research and its application vis-à-vis other methods of estimating dietary protein quality. This report of the FAO Expert Consultation on Protein Quality Evaluation in Human Nutrition considers the effectiveness and concerns about the PDCAAS method for evaluating protein quality concerning the PDCAAS method. A new method of dietary quality evaluation called DIAAS is recommended for application in practice.”


Current Concepts and Unresolved Questions in Dietary Protein Requirements and Sup-plements in Adults

Phillips SM. Front Nutr. 2017 May 8;4:13. doi: 10.3389/fnut.2017.00013. eCollection 2017    Link to publication


Protein needs for otherwise healthy individuals older than 19years are defined by the recommended dietary allowance (RDA) at 0.80g protein/kg/day. There is no recommendation in the current RDA for subpopulations of older adults or people in various pathological situations. Despite the lack of a separate recommendation, there exists a growing body of evidence that is strongly suggestive of an increased need and/or benefit for protein in older persons. That is, intakes beyond the RDA are, in older persons, associated with benefits. In addition, a number of catabolic states including critical illness also result in a sharp elevation in the needs for protein and amino acids. An underappreciated issue in protein nutrition is the impact of protein quality on clinically relevant outcomes. The introduction of a new protein scoring system-the digestible indispensable amino acid score (DIAAS)-for protein quality has raised a forgotten awareness of protein quality. The DIAAS, which replaces the protein digestibility-corrected amino acid score (PDCAAS), is based on ileal digestibility of protein and a different test protein than PDCAAS and has values greater than 1.0. The aim of this article is a brief review and summary recommendations for protein nutrition and protein requirements in populations who would benefit from more protein than the RDA. The emphasis of the review is on muscle protein turnover, and there is a discussion of the impact of protein quality, particularly as it applies to commercially available protein sources. The evidence for more optimal protein intakes is considered in light of the potential health risks of consumption of protein at levels greater than the RDA.”