Glycine is a conditionally essential amino acid–amino acids being the building blocks of proteins. This amino acid is conditionally essential because the body can normally produce it using other essential amino acids, but it may require supplementation when a person is ill. Glycine is the smallest amino acid and can rotate easily, making it useful for proteins that need to be pliable.
Since this amino acid can be produced by modifying existing essential amino acids in the body, consumption of glycine is not technically required unless one is fighting an illness. Though consumption of this amino acid is still strongly suggested, so as to allow the essential amino acids to fulfill their other purposes in the body.
Pork, turkey, soy, gelatin, molluscs, egg whites