Is L Carnitine safe for athletes at doses up to 6000 mg day? Consensus 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: The Energy Booster Your Body Loves Turn fat into fuel and power up your recovery with one of our favorite performance vitamins. Boosts metabolism & fat burning L Carnitine Side Effects & Risks L Carnitine is Underrated. New Meta Review Reminds Us Why.