L-carnitine supplements are advertised as performance enhancers and weight loss wonder drugs, but the evidence doesn't back up the marketing. Your liver and kidneys make all the carnitine your body needs unless you have a deficiency, which may require supplementation, but supplementing with L-carnitine has not been proven to result in faster or more permanent weight loss despite numerous studies. According to the University of Maryland Medical Center, there is anecdotal evidence that L-carnitine may help reduce fatigue and increase fat loss, but until there is evidence as to the supplement's safety and effectiveness, it cannot be recommended as a weight loss drug.
The Royal Melbourne Institute of Technology Study
The Royal Melbourne Institute of Technology's Department of Human Biology and Movement Science published a study in a 2000 edition of the "International Journal of Sport Nutrition and Exercise Metabolism" that questioned the validity of L-carnitine as a weight loss supplement. Participants were moderately overweight women who were paired according to matching body mass index -- one of the pair was given two grams of L-carnitine daily, while the other was given two grams of lactose. All participants walked four days per week at 60 to 70 percent of their maximum heart rate for 30 minutes. By the end of the eight-week study, none of the women showed any statistically significant changes in body mass or fat mass, and five of the women taking L-carnitine dropped out of the study after having diarrhea and nausea. The study concluded that L-carnitine is probably not useful for weight loss.
The Cornell University Study
Later in 2000, Cornell's College of Veterinary Medicine's Department of Clinical Sciences tested the effects of L-carnitine on a group of overweight house cats. The cats were divided into two groups, with one receiving 250 mg of a liquid L-carnitine daily, the other group receiving plain water. Both groups were fed only 60 percent of the calories needed for their size. Within 18 weeks, the cats receiving L-carnitine lost about 23 percent of their weight, while the cats receiving plain water lost about 19 percent. The study concluded that L-carnitine appears to be a safe weight loss supplement for obese cats, but because the control group lost almost as much weight as the L-carnitine group, it may be concluded that the severe calorie restriction had more to do with it. It is not clear how this study would translate to humans, because cats and humans have different physiologies. It does, however, indicate that L-carnitine should be investigated further.
The University of Halle Study
In 2002, Germany's University of Halle Institute of Nutritional Sciences published a study in the "Annals of Nutrition and Metabolism" that basically mirrored the 2000 cat study, except with rats. The rats were all fed a restricted diet, only this time, the diet was controlled to provide no carnitine. Half of the rats were fed an L-carnitine supplement, and the others were not. After 23 weeks, all the rats lost weight because of the calorie restriction, and all had lower levels of body fat. There was little difference between the rats who were given L-carnitine and those given a placebo, leading the researchers to conclude that L-carnitine supplementation did not result in additional weight loss. In fact, because the diet didn't contain carnitine and the placebo group still showed carnitine in their blood, it led researchers to believe that the body manufacturers all the carnitine it needs to burn fat.
The West Chester University Study
In 2005, the West Chester University's Department of Kinesiology published a study in the "International Journal of Vitamin and Nutrition Research" that sought to explore the effect of L-carnitine on the weight of postmenopausal women. The study used rats who had their ovaries removed, and allowed them free access to food spiked with L-carnitine. A subgroup of rats were taught to swim to investigate the difference made by cardiovascular exercise. Not only did L-carnitine not appear to increase weight loss in either the sedentary or active group, the rats fed L-carnitine actually gained weight. The researchers concluded that L-carnitine in the absence of a calorie-restricted diet would not be beneficial to postmenopausal women, but moderate exercise may be recommended.
References
- University of Maryland Medical Center: Carnitine (L-carnitine)
- "International Journal of Sports Nutrition and Exercise Metabolism"; L-Carnitine Supplementation Combined With Aerobic Training Does Not Promote Weight Loss in Moderately Obese Women; Villani RG, et al.; June 2000
- "Journal of Veterinary Internal Medicine"; The Clinical and Metabolic Effects of Rapid Weight Loss in Obese Pet Cats and the Influence of Supplemental Oral L-carnitine; Center SA, et al.; November-December 2000
- "Annals of Nutrition and Metabolism"; Effect of L-Carnitine on Weight Loss and Body Composition of Rats Fed a Hypocaloric Diet; Brandsch C, Eder K; 2002
- "International Journal of Vitamin and Nutrition Research"; L-carnitine Supplementation Does Not Promote Weight Loss in Ovariectomized Rats Despite Endurance Exercise; Melton SA, et al.; March 2005
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