L Carnitine Carnitine: the claims and why it may not work L Carnitine is Underrated. New Meta Review Reminds Us Why. Effect of chronic L carnitine supplementation on carnitine levels, oxidative stress and apoptotic markers in peripheral organs of adult Wistar rats ScienceDirect 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 Effect of Acute and Chronic Oral l Carnitine Supplementation on Exercise Performance Based on the Exercise Intensity: A Systematic Review