L-Carnitine is the active form of carnitine that plays a role in fatty acid metabolism and energy generation, while D-Carnitine cannot be used by the body for energy and can disrupt the function of L-Carnitine. L-Carnitine ( as L-Carnitine Tartrate) provides 1000mg of the purest and clinically-tested form of L-Carnitine for energy and metabolism. L-Carnitine works by transporting fatty acids from the cytoplasm to the mitochondria. Once in the mitochondria, a series of enzymatic reactions results in the breakdown of fatty acids to produce energy.