Out to score some protein?

The back of your protein powder container can refer to any variety of scores for measuring protein quality. Food scientist Eric McEntyre explains the meaning behind the numbers.

 

"There are numerous ways for determining protein quality, however Protein Digestibility Corrected Amino Acid Score (PDCAAS) is the most recently accepted by the US Food and Drug Administration and may be the most accurate.

 

"Some foods, especially plant foods, lack certain amino acids particularly essential amino acids, which are those that are essential to humans and must be supplied by food, since the body cannot synthesise them from other sources.

 

"When one or more different types of foods are consumed the proteins in those foods may supply the essential amino acids necessary to form a high quality protein. These are called complementary proteins because the amino acids supplied from them fill the weakness in one another."

 

Eric sums up the main scoring systems used for protein:

 

Biological Value (BV) is a measure of how efficiently food protein can be turned into body tissues. Foods that contain all 8 essential amino acids in a ratio most appropriate to human requirements are more efficiently incorporated into body tissue so therefore they have a higher biological value. To determine BV, protein retained in the body is compared to protein excreted (this is in the form of nitrogen) the ratio of retained to excreted determines BV. Egg white has a BV of 100, with other protein sources compared to this 'standard'.

 

Protein Efficiency Ratio (PER) compares the amount of weight in grams (g) gained by a growing rat after 10 days or more of eating a standard amount of protein (9% of its energy intake) from a single protein source to the (g) of protein consumed.

 

Chemical score is the amount of each essential amino acid in a gram of the food's protein, divided by an "ideal" amount for that essential amino acid per (g) of food protein. The ideal protein pattern is based on the minimal amount of each of the 8 essential amino acids needed per (g) of food protein. The lowest amino acid ratio calculated for any amino acid is its chemical score.

 

Protein Digestibility Corrected Amino Acid Score (PDCAAS) is a method that replaces PER evaluations of foods intended for children over 1 year of age and for non-pregnant adults. To determine PDCAAS the chemical score is determined which varies between 0.0 and 1.0. This score is multiplied by the digestibility of the protein (0.8-1.0) which gives the PDCAAS. The maximum value is 1. Milk proteins, egg and soy have a value of 1. For labeling purposes the protein listed is corrected to account for the PDCAAS for example if ½ cup of pasta provides 3g of protein then the value listed will be 1.2 g of protein because the PDCAAS is .4 (3g x 0.4)=1.2g