The bright and the dark sides of L carnitine supplementation: a systematic review Journal of the International Society of Sports Nutrition Springer Nature Link L carnitine is a naturally occurring amino acid structure that is made in the human brain, liver, and kidneys. L carnitine plays a critical role in energy production, as it converts fat into energy. If you're putting in the work but the scale isn't moving, your body might just need a little help tapping into its fat stores. That's where L Carnitine comes in. It's not a What Is Carnitine and Why Is It Important? The Amino Company