By: Dr. Richard Patton
When shopping for pet food, people usually look for the amount of protein listed on the bag. For comparative shopping, this can be useful information, but it ignores a very basic and important fact about protein.
Suppose I told you the score of the ball game between the Yankees and the Red Sox was 5. You’d look at me as either stupid or withholding information. You’d expect more information… like the rest of the score. Well, when evaluating protein, you need more information besides “amount” or “percent.” The percent protein on the bag is nearly useless information; only half the ball score. To make any sound judgment, besides the amount of protein, you must also know the quality of the protein.
There are two kinds of amino acids; those able to be made from diet components, and those required preformed in the diet. These are called essential (meaning they must be in the diet) and nonessential (can be made by the animal itself from other ingredients in the diet). The more essential amino acids there are in a protein, the higher the protein’s nutritional value. For example, the protein in egg is very high quality. This stands to reason, as an egg must become a complete creature without any further input. Egg protein has a high level of essential amino acids. Milk protein is high quality, also logical, as milk is the sole nourishment for a young mammal.
All proteins can be ranked for quality based on the amount of their essential amino acids. This ranking is referred to as “Biologic Value”. No protein contains more essential amino acids than egg protein, so egg protein is arbitrarily considered 100, or the best. Milk protein is ranked at 93. Beef and fish are 75. A Biologic Value of at least 75 is required to support the growth of young mammals. Most plant proteins are ranked below 75, animal source proteins are 75 or higher. Therefore diets strong in animal source proteins are going to be of higher biologic value.
The protein in rice is unique for a plant because it has a biologic value of 85. This is fortunate, as half of the world gets much of its protein from rice. It is possible, by careful formulation, to blend different proteins and achieve a sum that is higher in value than any one ingredient. And this is what pet food formulators do… hopefully. But when all you know is the amount of protein stated on the bag, it is not possible to assume anything about quality of that protein. If a pet food’s major ingredients are quality animal protein sources, it is safe to assume it is better protein quality.
His book, Ruined By Excess, Perfected By Lack, discusses the worldwide problem of overweight behavior—both of pets and people—is a critical aspect of any proper diet.