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Hilary Spruytenburg

Index - Click to read a topic
What is L-Carnitine?
The role of L-carnitine: How does it work?
What's Available: is it effective?
What do the studies show?
In Conclusion


L-Carnitine is a naturally occurring amino acid which plays a vital role in the metabolism of fat. It functions as a transporter of fatty acids into the mitochondria, the metabolic furnace of the cell.

L-carnitine was discovered in Russia, and one year later in Germany. The proper name, Carnitine, refers to the Latin origin, (carno, caris). Its structural formula was decoded in 1927, and its physiological significance was understood by the 1960's. ( L-carnitine is synthesized in the liver and kidneys, from two essential amino acids, lysine and methionine. This synthesis requires the presence of vitamins niacin, B6, and iron. Most (98%) of the carnitine supply resides in the body's muscle tissue. Approximately 80% of the amino acids our bodies need is endogenously synthesized, the remaining 20% are referred to as the essential amino acids. The supply of such aminos, like l-carnitine, must be supplemented exogenously. L-carnitine is available in the following food sources: red meat, diary products, avocado, and tempeh. Although a well balanced diet can provide approximately 75% of what the body is lacking, often conditions arise that make it difficult to obtain all the carnitine one needs.

It has been established that an adequate supply of l-carnitine is necessary for the maintenance of good health. L-carnitine transports long-chain fatty acids across the mitochondrial membrane to be metabolized. L-carnitine aids in the release of stored body fat, tryglycerides, into the bloodstream for energy. Tryglycerides are the major source for the production of energy in the heart and skeletal muscles. Access to l-carnitine is believed to increase energy levels for long-term aerobic activity. L-carnitine is also responsible for muscle contraction, regulation of protein balance and maintenance of a healthy heart. Research also suggests that an adequate supply of l-carnitine could be instrumental in the treatment of diabetes, chronic fatigue syndrome, kidney and liver disease. ( Since its involvement in the process of burning fats is of most importance to those interested in endurance and body fitness, it is this topic that will be focused upon.


Carnitine boosts energy by stimulating the body's burning of tryglycerides as fuel, and sparing the supply of glycogen stored in the liver for heavier exertion. During exercise, the body will burn fat at a rate of 75-80% of maximum exertion, thus less glycogen from carbohydrates is burned. L-carnitine allows the body to burn more fat, save more glycogen, and ultimately boost stamina and endurance. By providing more fat to the muscles, carnitine makes accessible an otherwise unavailable energy source. (


Is this the recipe for success? According to proponents of L-Carnitine, it is the essential amino acid in the optimum fat burning process. They believe that carnitine is to the human body, what a turbo mechanism is to a car: both provide optimal fuel and performance. Minus L-carnitine, fatty acids would have a difficult time permeating the walls of the mitochondria. Energy, stored in carbohydrates and fats, is required to work the muscle. Carbohydrates are converted from glucose to glycogen, to be stored in liver and muscle cells. Eventually, the body turns to fat storage for energy, and possibly, with more ease in the presence of L-carnitine. This is where L-carnitine as a supplement enters. During high energy output, the supply of L-carnitine becomes exhausted. Is it possible to compensate for this decrease solely through metabolic processes and diet? Or is an additional carnitine supplement needed for the extra boost? Judging from the variety of carnitine products now on the market, apparently many believe an additional outside source proves beneficial.


On the market today, exists a wide domain of ergogenic (or "energy boosting") aids, designed to enhance performance and to create a leaner, trimmer and more beautiful body. L-carnitine is found in many of these products. The amino acid is considered so potent that it is as equally often packaged independently, as it is compounded with other ingredients. Briefed here are several l-carnitine supplements readily available. Each product's marketing adheres to the fundamental claim that L-carnitine increases the amount of fat burned, thus increasing energy and lean muscle mass.

1. "MEGA BURN L-CARNITINE is the body's ultimate source of pure natural L-Carnitine." This product, available in both pill and liquid form, is in a base of purified water, vegetable glycerine and pantothenic acid (vit B5). It claims to reduce body fat, aid in weight loss and help to reshape bodies. Individuals who took Mega-burn reported an average weight loss of 3-5 lbs. per week, increased energy and found it easier to lose those "stubborn pounds". One fitness consultant claims it had him "ripped for his show". (

2. "MULTI-POWER CHEWABLE L-CARNITINE, The Newest Internationally Accepted Endurance Enhancer!" should be chewed just before a workout to improve performance, increase stamina and provide a quicker recovery from an intensive workout. (

3. "OPTIMUM NUTRITION LIQUID L-CARNITINE 1000 is a highly potent and fast absorbing source of pure L-Carnitine." It also contains pantothenic acid and vitamin B5, for accelerated metabolism. (http://

4. "NATURALLY RIPPED is a herbally balanced fat burning formula supplement containing a metabolic enhancing formula." In addition to L-carnitine, it contains MaHuang, and Guarana. It, too, is taken before a workout on an empty stomach. (http;//

5. "ULTRA FAT SOLVE With L-Carnitine 500MG is a synergistic blend of Amino Acids, Minerals, Lipotrophic Factors, Unsaturated Fatty Acids and Vitamins designed to enhance the weight loss process." Designed to burn fat and nutritionally support the heart. (Global Nutrients, 1995)

6. "TONE 'N' TRIM is a powerful fat metabolizing and weight control supplement designed especially for women." It contains Citrimax, which utilizes glycogen storage to initiate satiety and is to be taken before meals. (

7. "AMERICAN BODY BUILDING'S CARNITINE" . . .Each capsule provides 500mg of pure L-Carnitine helping you mobilizing the fat" (

To address the question, "Is L-Carnitine Effective?", it becomes necessary to look beyond advertised claims. Understandably, manufacturers support their products, and are thus biased. Likewise, individual testimony most frequently arises from successful trials with L-carnitine. In order to provide a full-spectrum report, we now turn to information evidenced in non-promotional sources.


Recent research done on L-carnitine shows mixed results concerning its effectiveness. A number of journal studies involving the administration of l-carnitine to both human participants and animal subjects reveals both adverse and positive results. In Training and Nutrition, J. P. Krabbe (1996) reports that although L-carnitine is important in the correction of human carnitine deficiency, once such a deficiency is corrected, more is unnecessary. Since humans get plenty of it from meat and diary products, most healthy individuals exceed the recommended daily dosage. Krabbe writes, "Also true is that once any deficiency is corrected, that the majority will get excreted. Thus, more is not better, unless you need it." (http;//

Such a case is reported in the Journal of Clinical Neurology. A woman showed secondary carnitine deficiency as a result of anorexia nervosa and liver damage, which rendered her liver incapable of synthesizing l-carnitine (Negoro, Tsuda, Kato & Morimatsu, 1995). Her deficiency was treated with oral administration of L-carnitine.

M. H. Williams (1992) researched the use of ergogenic aids among endurance athletes, and found L-carnitine to be ineffective. Factors that did in fact enhance performance were genetic endowment, proper training and nutrition, and an adequate supply of fluids and carbohydrates. Conversely, McCarty (1995) found that carnitine may promote weight loss in exercise regimens by enhancing glucose homeostasis in the liver. At the Nestle Research Centre, researchers studied the effect of L-carnitine on exercise metabolism after depletion of muscle glycogen. Nine healthy male subjects received L-carnitine or a placebo and then were submitted to 60 minutes of exercise after an overnight fast. It was concluded that metabolism was not influenced by carnitine supplementation (Decombaz, Deriaz, Acheson, Gmuender & Jequier, 1993). A similar study found that during submaximal exercise, carnitine supplementation did not result in increased lipid oxidation or muscle carnitine content, indicating that the administered carnitine was not absorbed by the body (Vukovich, Costill & Fink, 1994).


Is L-carnitine a safe and effective means of enhancing fat metabolism? The evidence presented here reports no harmful side effects. Product reports contest that l-carnitine works by transporting fatty acids to be burned for fuel, increasing both energy supply and lean muscle mass. Studies show a more skeptical look at the product. Most found that unless an individual is deficient in l-carnitine, it is an unnecessary ergogenic aid. I conclude that as with other vitamins, minerals and medications, L-carnitine is as effective as the consumer's belief in the product.


1. Decombaz J., Deriaz O., Acheson K., Gmuender B., & Jequier E. (1993). Effect of L-carnitine on submaximal exercise metabolism after depletion of muscle glycogen. Medicine & Science in Sports & Exercise, 25 (6): 733-40.

2. Fukusako T., Negoro K., Tsuda N., Kato M., & Morimatsu M. (1995). A case of secondary L-carnitine deficiency due to anorexia nervosa and severe liver damage. Clinical Neurology, 35 (1): 34-7.

3. Krabbe J. P., (1996). L-Carnitine. Training- Nutrition, 332. (

4. McCarty M. F., (1995). Inhibition of citrate lyase may aid aerobic endurance. Medical Hypotheses, 45 (3): 247-54.

5. Vukovich M. D., Costill D. L., Fink W. J., (1994). Carnitine supplementation: effect on muscle carnitine and glycogen content during exercise. Medicine & Science in Sports & Exercise, 26 (9): 1122-9.

6. Williams M H., (1992). Ergogenic & ergolytic substances. Medicine & Sports in Sports & Exercise, 2 (suppl 9): S344-8.


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