L-carnitine is a product of two of the essential amino acids that the body cannot produce on its own: lysine and methionine. L-carnitine is often referred to as a vitamin-like molecule because it is synthesized in the liver and kidneys from the amino acid lysine and other nutrients. At a basic cellular level, L-carnitine plays a critical role in the metabolism of fat, contributing to the oxidation of fatty acids and transporting long-chain fatty acids to the place in the cells (mitochondria) where they are processed to help provide energy, among other things.