The protein efficiency ratio (PER) is defined as:
|A||The gain in weight of young animals per unit weight of protein-consumed|
|B||The product of digestibility coefficient and biological value|
|C||The percentage of protein absorbed into the blood|
|D||The percentage of nitrogen absorbed from the protein absorbed from the diet|
a. Since it is impossible to measure weight gain in grams in humans, PER is generally measured in young, growing animals placed on a diet which is 10% protein by weight. This begs the question of whether young animals, who are growing, provide a good model for adult humans.
b. While the Food and Drug Administration has suggested the use of PER with casein as a reference model for labeling protein foods, the use of PER to estimate human protein requirements has been criticized by some author.