Knowing nothing of humans, which are harder to study because they live so much longer, grow to adulthood so much slower, and metabolize food so much slower, nutritional scientists applied what they had learned about rats to humans. The conclusion was that animal sources of protein were superior to plant sources for human nutrition because of the higher concentration of protein. In the early 1950s, definitive studies were conducted on human beings, and the eight essential amino acids were identified. Both animal and plant sources of amino acids provide an abundance of the essential amino acids. As it turns out, the amino acid needs of human beings can be met better by some plant sources, such as soy, because plant protein comes without the heavy load of fat present in meat, milk and eggs.
Milk is said to be a good source of protein.
Perhaps so, but the problems associated with pasteurized milk and milk products make it a less than desirable source. At first glance, it may seem that animal sources of protein would be superior because of the higher concentration of protein. However, as it turns out, the body cannot distinguish the source of protein, or the concentration, only the total amount. The problem with meat is what has been added to the meat in production such as antibiotics, hormones, pesticides and herbicides found in cattle and pig feed. An ideal intake of protein is 0.8 grams per kilogram of body weight.