L-Carnitine was first discovered by two Russian scientists in muscle extracts from which substance got its name (Latin word carnis – flesh or meat). [1] Carnitine is biosynthesized from the amino acids lysine and methionine [2]. In the terms of bioavailability Acetyl-l-carnitine is claimed to be superior to L-carnitine [3].
L-carnitine has been increasingly popular as a potential ergogenic aid because of its role in the conversion of fat into energy [4]. The most important claim relates to the role of carnitine in fat metabolism. It is often advertised that L-carnitine benefits in fat metabolism, fat mass reduction, and increases muscle mass. In other words, it is sold as “fat burner”. Its claims for a weight loss agent are based on the assumption that oral supplementation increases intracellular concentrations of L-carnitine. This would increase the fat oxidation and reduce body’s fat reserves.[5] However, several studies have shown that oral carnitine ingestion does not change muscle carnitine levels and does not promote weight loss [6,7]. A study in animals reported that dietary carnitine stimulates carnitine palmitoyltransferase (or carnitine acyltransferase 1), [8] which could explain the increased appetite by L-carnitine supplementation [5].
So, claims that l-carnitine supplementation promotes weight loss are not sufficiently justified, especially for healthy non-obese individuals.
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References
- Gulewitsch WKR. Zur Kenntnis der Extraktionsstoffe der Muskeln. 2. Mitteilungen über das Carnitin (extracted substances in muscle, report on carnitine). Hoppe-Seyler Z Physiol Chem 1905;45:326
- Steiber A, Kerner J, Hoppel C (2004). “Carnitine: a nutritional, biosynthetic, and functional perspective”. Mol. Aspects Med. 25 (5–6): 455–73.
- Hosein, E. A., and Jennie M. Smoly. “Biosynthesis of acetyl-l-carnityl choline.” Archives of Biochemistry and Biophysics 114.1 (1966): 102-107.
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Cerretelli, P., and C. Marconi. “L-carnitine supplementation in humans. The effects on physical performance.” International journal of sports medicine 11.01 (2008): 1-14.
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Karlic, Heidrun, and Alfred Lohninger. “Supplementation of L-carnitine in athletes: does it make sense?.” Nutrition 20.7 (2004): 709-715.
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Barnett, C., et al. “Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling.” International journal of sport nutrition 4.3 (1994): 280.
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Villani, Rudolph G., et al. “L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women.” International Journal of Sport Nutrition 10.2 (2000): 199-207.
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Karlic, Heidrun, et al. “Dietary l-carnitine stimulates carnitine acyltransferases in the liver of aged rats.” Journal of Histochemistry & Cytochemistry 50.2 (2002): 205-212.
