Lysine is an essential amino acid. Lysine along with the amino acid methionine is used by the body to synthesize L-carnitine, which helps cells break down fat in the body and in so doing helps the body to produce energy. Lysine, in conjunction with the amino acide L-arginine, is necessary for collagen sybthesis and so plays an important role in the building and production of skin cells, ligaments and tendons.