Proteins in the Diet z 9 of the 20 amino acids must be obtained from the diet z These are referred to as the essential amino acids. – Histidine – Isoleucine – Leucine – Lysine – Methionine – Phenylalanine – Threonine – Tryptophan – Valine z Proteins are also the major source of nitrogen in the dietProteins in the Diet z 9 of the 20 amino acids must be obtained from the diet z These are referred to as the essential amino acids. – Histidine – Isoleucine – Leucine – Lysine – Methionine – Phenylalanine – Threonine – Tryptophan – Valine z Proteins are also the major source of nitrogen in the diet