Amino acids

    Essential amino acids must be derived from the diet and cannot be synthesized by the body. Some amino acids are semi-essential, or conditionally essential, meaning they can be synthesized in the human body in a certain developmental stage or in healthy states. Conditionally essential amino acids are needed more in times of illness and stress. Of the 20 amino acids commonly found in proteins, 9 are considered essential for humans including histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Two conditionally essential amino acids are also included: arginine and taurine. 

    Nonessential amino acids are synthesized by the body from amino acids and other intermediates. Although they can be obtained from the diet, it is not required (unlike essential amino acids). However, when dietary intake of protein is very limited, both essential and nonessential amino acids may trend low.