9 Best Supplements for Polycystic Ovarian Syndrome (PCOS) Role of L carnitine in female infertility Reproductive Biology and Endocrinology Springer Nature Link How L Carnitine Helps with Fat Metabolism Polycystic Ovary Syndrome (PCOS): Symptoms & Nutritional Strategies. Life Extension L carnitine is a naturally occurring amino acid structure that is made in the human brain, liver, and kidneys. L carnitine plays a critical role in energy production, as it converts fat into energy.