He concluded that without the presence of certain amino acids from protein in the diet, life processes would cease. In other words, there are essential amino acids that we must consume in our diets because they cannot be manufactured by our bodies. Interestingly enough, in critically ill patients, in the management of certain pathological conditions, and in serious injury, demands may vary. We'll discuss these and similar issues in a future article in this series. The nutritional value of various proteins is often measured by a unit of worth called biological value.
Biological value is a measure of the food nitrogen in protein that the body retains.
The more nitrogen from ingested protein that is actually retained in the body, the better the quality of the protein is assumed to be. It turns out that the biological value of beef protein is 0.67, whereas the biological value of wheat protein is 0.42. This is consistent with the original observations that animal protein diets yielded better growth and performance than vegetable protein diets. Remember, too, that scientists were curious to know why the value of the proteins differed. Once they understood that certain amino acids were essential, they began investigating just how much of each was essential.