The Benefits (and Limitations) of L Carnitine for Fat Loss L Carnitine The Wonder Fat Loss Miracle or Just Marketing Hype? FIT Asia Advancing Fitness Education 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 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.