L Carnitine Benefits for Fat Burning and How to Use ICONFIT L Carnitine Vitamin Supplement for Energy and Metabolism Boost L Carnitine 1000mg Energy, Metabolism & Fat Burning Acetyl L Carnitine vs L Carnitine: 4 Key Differences Momentous 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.