When to Take L Carnitine for Optimal Training Benefits Transparent Labs 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 Linus Pauling Institute Oregon State University 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. Why To Much L Carnitine Is Unhealthy L Carnitine and Sleep: Does It Affect Rest or Sleep Quality?