While many supplement manufacturers claim that L-carnitine can speed up metabolism, there is little scientific support for L-carnitine's ability to promote weight loss.
Health Benefits of L-Carnitine for Weight Loss
To date, few clinical trials have tested l-carnitine's effectiveness as a weight loss aid. The available research includes a 2000 study from the International Journal of Sport Nutrition and Exercise Metabolism, in which 36 moderately overweight premenopausal women were given either L-carnitine or a placebo twice daily for eight weeks. Analyzing study results, researchers found no difference in total body mass or fat mass between those who took L-carnitine and those given the placebo.
A number of animal studies have also shown that L-carnitine may not support weight loss. A 2002 study from the Annals of Nutrition and Metabolism, for instance, found that rats treated with l-carnitine did not experience a greater reduction in body fat levels compared to a control group.
What's more, a 2005 study published in the International Journal for Vitamin and Nutrition Research found that rats fed an L-carnitine-enhanced diet tended to gain more weight than other animals in the study (despite no difference in their intake of calories).