L carnitine: what it is, functions & types Marnys Potential Adverse Effects of L Carnitine Marnys L Carnitine Benefits for Fat Burning and How to Use ICONFIT 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 Is L Carnitine safe for athletes at doses up to 6000 mg day? Consensus 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.