This is a guest blog post by Richard Perlmutter, MS
For most nutrients it is easy to understand how the % Daily Value (%DV) is determined. It is simply the percentage of the 100% Daily Value amount that is in a serving of food. The 100% DV is regarded as the amount of a nutrient that will satisfy the requirement for the nutrient in 97% – 98% of all adults.
Calcium serves as a good example. The 100% DV is 1000mg. A serving of milk has 300mg, which is 30% DV.
What is simple for calcium is not at all simple for protein. Please notice the grams of protein and the %DV protein in the three Nutrition Facts panels above:
- For Milk – 8g protein which supplies 16% of the Daily Value.
- For Peanuts – 7g protein which supplies 7% of the Daily Value.
- For Kidney Beans – 8g protein which supplies an unstated % of the Daily Value.
A testing procedure with the abbreviation PDCAAS is responsible for the various %DVs. The initials stand for Protein Digestibility Corrected Amino Acid Score.
Proteins differ in how useful they are in the body and the Score is a measure of that usefulness. This test method was accepted in the early 1990s by the Food and Agriculture Organization of the United Nations, and by the federal Food and Drug Administration (FDA) a short time later.
The test to determine the PDCAA Score is complicated. It requires knowing both the digestibility of the protein (as determined in animal feeding studies) and the amounts of each essential amino acid in the protein. The amino acids that the body cannot make, and that must come from food intake, are the essential amino acids.
Due to the testing difficulty, the Score has been determined for protein from only about fifteen sources. Several types of beans have been tested, but not kidney beans.
In general, proteins from animal sources have a Score between 0.9 and 1.0. A huge exception is gelatin. Because it almost completely lacks one of the essential amino acids, it has a Score of 0.
Proteins from plant sources vary in their Score. Soy protein has a 1.0. Wheat protein has a 0.4. And peanut protein has a 0.5. Milk protein is of very high quality and its PDCAA Score is 1.0, which is the highest Score value allowed. Peanut protein, with a Score of 0.5, is of lesser quality. Peanut protein provides half of the %DV as the same amount of milk protein.
Two of the Nutrition Facts panels above show that 50g protein is recommended in a two thousand calories per day diet. The third − for kidney beans − does not have the information.
The FDA requires that the PDCAA Score be used when determining the %DV for protein. For example, the %DV protein for a serving of peanuts is calculated as: 100 x PDCAAS x (g protein per serving/50g).
- %DV peanut protein which has a Score of 0.5: = 100 x 0.5 x 7g/50g = 7%DV.
- For milk protein which has Score of 1.0: %DV = 100 x 1.0 x 8g/50g = 16%DV
It is optional to include the %DV for protein in the Nutrition Facts panel, even when the PDCAA Score is known. An exception to this is that the %DV must be stated if there is a front-of-package nutrition claim for protein. “Good source of protein” is an example of such a claim. There are also specific regulations when a food is intended for children less than 4 years of age, infants, pregnant women, and lactating women.
As complicated as the PDCAAS test procedure is, the United Nations is proposing to replace it with an even more complicated test. Assuming the Food and Agriculture Organization of the United Nations adopts the new procedure, the FDA will likely do so also. Then the %DV protein will be based on the new test.
The new procedure will determine the Digestible Indispensable Amino Acid Score, or DIAAS. Indispensable replaces essential as the adjective used to describe the amino acids in protein that the body cannot make.
It will differ from the current test by measuring protein digestibility, the amount of protein absorbed by the body, more accurately. The current test measured protein absorbed by the body plus protein that nourishes gut bacteria.
The test will also measure each indispensable amino acid for loss of bio-availability. The amino acid lysine is given as an example. It loses functionality when subject to certain food processing operations. The DIAA Score will account for this loss.
Some high quality animal-sourced proteins, including the protein in milk, have a Score around 1.2 using DIAAS. Unlike the current test, DIAAS does not impose a 1.0 maximum for the Score. Dairy interests are advocating for the new testing procedure because they want to use the higher Score when calculating the %DV for protein.
The DIAAS test developers expect it may take five years to confirm that the test is reproducible, and to determine the Score for the major proteins in foods. That is how long it may be before the PDCAAS method is replaced.
Richard Perlmutter is the owner of Abington Nutrition Services LLC which prepares nutrition labeling for products manufactured by food and beverage companies. He also takes an interest in seeing that government nutrition policy is in line with nutritional science.