“The match between dietary supply and human protein needs is vital to support the health and well-being of human populations,” said Sukh Gill, Llb, DTS, MTSI, Director of Global Regulatory Services, Leatherhead Food Research, while quoting a 2011 FAO Report. However, regulations around the globe take inconsistent approaches to define the amount and quality of dietary protein required by humans.
When an over-simplified regulatory approach is taken in providing information about a food’s protein quality or content, less informed choices may result, as that information is used to make decisions on how to meet nutritional needs. More sophisticated approaches to determine protein quality and quantity help level the playing field for making protein marketing claims. Also, global food policies will be able to give higher priority to dietary sources of protein that best deliver against population needs, noted Gill.
In the late 1800s, Johan Kjeldahl developed an analytical method based on a food’s nitrogen content to determine protein quantity in grain. His method remains internationally recognized; however, since it includes non-protein nitrogen, it does not always measure the true protein content of a food.
Kjeldahl’s method also does not measure a protein’s nutritional value, which is related to its ability to satisfy nitrogen and amino acid requirements for tissue growth and maintenance, said Gill. Current thought is that this ability primarily depends on the digestibility of protein and amino acids, and the dispensable and indispensable amino acid composition of the proteins. [NOTE: The EU and U.S. differ in requirements needed to make a protein claim] (See chart “EU vs. U.S.: Making a Protein Claim.”)
In the U.S., from 1919 until 1993, the Protein Efficiency Ratio (PER) was the method used to evaluate the quality of protein in a food. In 1993, the more sophisticated Protein Digestibility Corrected Amino Acid Score (PDCAAS) rating was adopted by the US FDA and the FAO/WHO (but not the EU) for determining protein quality.
PDCAAS is based on the amino acid requirements of humans and their ability to digest them. Proteins can have scores from 0 to 1. It, too, has limitations. For example, the formula used to calculate PDCAAS can result in scores over 1.0 for some high-quality proteins, but 1.0 is the maximum score allowed—which limits its usefulness as a comparative tool. By combining foods with low PDCAAS values, a high PDCAAS can result.
“Should we then consider from a whole diet, rather than a single-food perspective?” asked Gill. “For nutrition labelling, a whole-diet approach makes sense; from a marketing perspective, claims are made on single foods.” Also, PDCAAS doesn’t address whether the true ileal digestibility of protein is preferable to the faecal measurement of protein.
For these and other reasons, the FAO has recommended replacing PDCAAS with the Digestible Indispensable Amino Acid Score (DIAAS). DIAAS equals 100 x [(mg of digestible dietary indispensable amino acid in 1g of the dietary protein) / (mg of the same dietary indispensable amino acid in 1g of the reference protein)].
However, DIASS also has issues. For example, more data on the true ileal amino acid digestibility of human foods is needed in the calculation of DIAAS. Until that becomes available, it is suggested that digestible individual dietary amino acid values should be calculated using faecal crude protein digestibility values applied to dietary amino acid contents.
If resources are not allocated to complete this research objective in a timely manner, current recommendations for the application of DIAAS may need to be reviewed.
Sukh Gill, Llb (Hons), DTS, MTSI, Director of Global Regulatory Services, Leatherhead Food Research, firstname.lastname@example.org, +44 (0)1372 376761, www.leatherheadfood.com/