l carnitine: Nutrition, pathology, and health benefits ScienceDirect L Carnitine and Sleep: Does It Affect Rest or Sleep Quality? 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 are like a lot of people, you may have never heard of carnitine but this important nutrient is critical for our body's ability to optimally burn fat required for energy. Are L Carnitine and L Carnosine the Same? Anti Aging Systems The Benefits (and Limitations) of L Carnitine for Fat Loss