REQUIREMENTS FOR LABELING FOODS AS PROTEIN SOURCES

Current dietary guidelines, including those in Canada and the United States, have advocated for the inclusion of more plant protein in the diet.^1,2

For countries within the European Union as well as the United Kingdom, protein content claims are classified on the basis of protein content relative to energy content. Food products containing a minimum protein content of 12% of the energy value can carry a “source of protein claim.” Products with a protein content of 20% or higher can use the term “high protein.”³

In Canada and the United States, protein content claims on labels must be substantiated based on both protein quantity and quality. In Canada, the official method for substantiating protein content claims is the Protein Rating system, which until recently was based on the use of the Adjusted Protein Efficiency Ratio (PER) alone, determined using a rat growth bioassay.^4,5

Several challenges with the PER measurement have been recognized,⁶ and as such, calls for the modernization of the Canadian protein content claim regulations were recently published.⁷ In December 2020, Health Canada announced that it would permit the use of an alternative method in calculating the Protein Rating of foods.⁸ The newly allowed method is based on the Protein Digestibility-Corrected Amino Acid Score (PDCAAS), the official method used in the U.S.⁹

The U.S. Food and Drug Administration (FDA) requires the use of the PDCAAS method, as described in the 1991 Food and Agriculture Organization of the United Nations (FAO) report,¹⁰ for the presentation of a percent daily value for protein on the nutrition facts panel as well as the substantiation of protein content claims on labels. PDCAAS is a numerical value based on the true fecal protein digestibility (TFPD%) of the protein in question and the amino acid score of the protein, which is measured as the lowest ratio value of the food-based amino acid content (mg AA/g protein) relative to a reference amino acid pattern.¹⁰ As is the case with PER, in order to officially determine protein digestibility (TFPD%), a rodent bioassay is required. In addition to a measure of digestibility, the amino acid composition of the food protein is a critical factor in establishing the overall PDCAAS value.

If the value of an amino acid score is 1.0 or greater, the protein in question provides all the indispensable amino acids at a rate greater than that required by humans. Many plant proteins present with deficiencies in key indispensable amino acids, namely lysine (grains/cereals, nuts, seeds), the sulphur amino acids methionine and cysteine (pulses), and tryptophan (pulses).¹¹ For many plant proteins, amino acid scores typically range between 0.4-0.9, with substantial variability due to factors including plant genetics, environmental conditions, and processing.¹⁰ Certain plant-based proteins (e.g., soy protein isolate) can present with scores of 1.0 or greater, but higher values are typically observed with animal protein sources or with complementary blends of plant-based sources (grains/cereals and pulses).

In considering the other variable that makes up PDCAAS, the digestibility of plant proteins can be influenced by the presence of certain anti-nutritive factors known to suppress protein digestion (e.g., trypsin inhibitors in beans) and the presence of plant-cell wall components.¹² The latter factor can be substantially influenced by processing, including both the concentration and isolation of proteins (e.g., production of soy or pea protein isolates), and thermal processing.¹³ When both the amino acid score and the TFPD% variables are determined, using official methods, the resultant product of these 2 measures will yield the final PDCAAS value. Values greater than 1.0 are capped.¹⁰ The resulting PDCAAS value is used to establish the corrected amount of protein within a representative serving (grams crude protein in serving times PDCAAS) in relation to the daily value of 50g of corrected protein. When foods present with 5g (10% of daily value) or more PDCAAS-corrected protein, they are allowed to carry a “good source of protein” claim. Foods with 10g of protein (20% of daily value) or more can carry an “excellent source of protein” claim.⁹

Several developments have emerged with respect to the potential modernization of protein content claim regulations. In 2013, the FAO proposed a new method for measuring protein quality. Since both the Canadian Protein Rating and PDCAAS methods have been criticized on the basis of their relative ability to predict the availability of amino acids for human nutritional needs,¹⁴ the FAO proposed the Digestible Indispensable Amino Acid Score (DIAAS) method.¹⁴ The DIAAS method is conceptually similar to the PDCAAS method; however, DIAAS uses updated amino acid reference patterns, sets the score as the lowest value for ileal digestible amino acids (end of small intestine), and does not cap values when they are higher than 1.0.

While this method offers several theoretical improvements over the Protein Rating and PDCAAS approaches, it has not been officially adopted by any jurisdiction. Furthermore, DIAAS continues the reliance on animal-based bioassays which creates a challenge for the plant protein sector seeking health claims for their food labels. Many food production companies are limited in their ability to use animal testing because of regulatory restrictions due to societal concerns. Without testing, food companies are unable to include health claims on the label; and therefore, consumers are unable to utilize this information to make decisions. Alternative approaches, including the use of in vitro methods for measurement of protein/amino acid digestibility⁶ could be considered by regulatory authorities to alleviate this messaging impediment.

Click here to view an infographic outlining how PDCAAS and DIAAS are used to classify foods as “good” or “excellent” sources of protein.

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