That means that a cat must eat several different sources of protein in order to obtain all 11 of the essential ones. The proteins from meat contain a greater variety of amino acids than do proteins from plants. All 23 amino acids must be present and available in order for the body to synthesis proteins. That means that if a cat takes in a meal that is deficient in any one amino acid, protein synthesis stops. The available amino acids are then burned for energy.
Excess energy is stored as fat, and ammonia is released as a waste product.
The same holds true if protein is consumed in excess amounts from what is needed to manufacture the body's structual proteins. This becomes very important in diseases like obesity and kidney disease . Protein, in fact, is a very questionable and controversial energy source, and in most healthy animals should be avoided in excess. The cat is unique among animals, however, because the cat is one species that actually requires some of its energy to come from protein. This is one reason why cats require more protein in their diet than dogs.