Early research into L carnitine was often cited as underwhelming, showing negligible changes in muscle carnitine content and fat loss outcomes. However, these findings may have been limited by a short study window L carnitine is effective for both fat loss and athletic performance. However, oral L carnitine has lower bioavailability and can be harmful at high doses, so it should be avoided. , Even cardiologists L Carnitine Linus Pauling Institute Oregon State University The Role of L Carnitine in Kidney Disease and Related Metabolic Dysfunctions