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. Is L Carnitine safe for athletes at doses up to 6000 mg day? Consensus L Carnitine is Underrated. New Meta Review Reminds Us Why. 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