L-lysine, an essential amino acid, cannot be synthesized in the body. Vegetarians can be deficient in lysine because, while meat, poultry, and milk are rich sources of lysine, proteins in grains and cereals are typically low in lysine. Of the many biological functions requiring lysine, some notable applications include synthesis of connective tissues such as bone, skin, collagen, and elastin; synthesis of carnitine and the resultant conversion of fatty acids to energy; support for healthy growth and development in children; and maintenance of a healthy immune function.*