L Carnitine: Benefits, Side Effects, Sources, and Dosage iMuscles Nutrition 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. Supplement of the week: L Carnitine! This one doesn't just boost fat metabolismit can also improve recovery, endurance, and even brain function. If you're serious about performance and longevity, this might be