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Majid Koozehchian, MS


L-Carnitine and Weight Loss:

L-carnitine (CARN) is a trimethylamine molecule being synthesized in mammals from essential amino acids lysine and methionine in the kidney, liver, and brain or ingested through diet. CARN is a cofactor of carnitine palmitoyl transferase and serves as a transporter of long-chain fatty acids such as triglycerides across the mitochondria for β-oxidation (1, 2); therefore, CARN supplementation may increase lipid metabolism and promotes a decrease in fat mass. CARN ingestion may influence plasma CARN concertation, stimulate weight loss in animals (3), and improve β-oxidation in adults (4). The rationale for CARN ingestion as a weight-loss agent is based on the assumption that elevated cellular levels of CARN could theoretically increase transport of fats into the mitochondria and thus provide more substrates for fat metabolism (5). This would stimulate elevated β-oxidation and gradual reduction of fat reserves; however, the use of CARN as a weight loss dietary supplement yields inconsistent results. The results of some studies indicated that oral CARN ingestion does not stimulate weight loss in overweight or trained subjects (6-8). This is not in line with clinical studies finding the beneficial role of supplementary CARN in the management of obese individuals (9). It has been indicated that inhibition of hypothalamic carnitine palmitoyltransferase-1 decreases food intake (10). Dietary CARN stimulates function and transcriptional rate of carnitine palmitoyltransferanse (11), which explains a stimulation of appetite by CARN supplementation. Consequently, claims that CARN supplementation promotes weight loss in humans are not sufficiently evidenced and need to be investigated in more detail.

L-Carnitine and Recovery from Exercise:
CARN is important for normal muscle bioenergetics for at least three reactions: CARN transports required fatty acid for β-oxidation; it assists in regulation of the mitochondrial acyl-Co A / CoA ratio, and stabilization of cell membranes; and it assists in detoxification of potentially toxic metabolites, and stabilization of cell membranes (12). The ideal performance of metabolic processes is essential during severe exercise. Hypothetically, CARN availability may be the limiting factor for β-oxidation or the removal of acyl-CoA during exercise. If this is true, CARN supplementation in healthy individuals should improve exercise performance. The ergogenic benefits of CARN for endurance exercise is based on three assumptions. The first hypothesis mentions that the existing CARN concentration in muscles would be too low to allow carnitine acyltransferases to function at a high rate and to support the elevated rate of fat oxidation during exercise. Second, oral ingestion of CARN should increase total muscle CARN concentration. Third, this increase in muscle CARN should elevate rate of oxidation of intramuscular fatty
acids during exercise, thereby reducing muscle glycogen depletion and delaying fatigue (13). During severe exercise, the free CARN concentration in muscle will decrease because the compound reacts with acetyl-CoA. During severe exercise, the free CARN concentration may drop to very low levels, which is a possible mechanism for the reduction of plasma fatty acid and intramuscular triacylglycerol oxidation during severe exercise (14).

References

1.       Kraemer WJ, Volek JS, Dunn-Lewis C. L-carnitine supplementation: influence upon physiological function. Current sports medicine reports. 2008;7(4):218-23.

2.       Kerner J, Hoppel C. Fatty acid import into mitochondria. Biochimica et biophysica acta. 2000;1486(1):1-17.

3.       Center SA, Harte J, Watrous D, Reynolds A, Watson TD, Markwell PJ, et al. The clinical and metabolic effects of rapid weight loss in obese pet cats and the influence of supplemental oral L-carnitine. Journal of veterinary internal medicine / American College of Veterinary Internal Medicine. 2000;14(6):598-608.

4.       Muller DM, Seim H, Kiess W, Loster H, Richter T. Effects of oral L-carnitine supplementation on in vivo long-chain fatty acid oxidation in healthy adults. Metabolism: clinical and experimental. 2002;51(11):1389-91.

5.       Kreider RB, Wilborn CD, Taylor L, Campbell B, Almada AL, Collins R, et al. ISSN exercise & sport nutrition review: research & recommendations. Journal of the International Society of Sports Nutrition. 2010;7:7.

6.       Abramowicz WN, Galloway SD. Effects of acute versus chronic L-carnitine L-tartrate supplementation on metabolic responses to steady state exercise in males and females. International journal of sport nutrition and exercise metabolism. 2005;15(4):386-400.

7.       Lee JK, Lee JS, Park H, Cha YS, Yoon CS, Kim CK. Effect of L-carnitine supplementation and aerobic training on FABPc content and beta-HAD activity in human skeletal muscle. Eur J Appl Physiol. 2007;99(2):193-9.

8.       Villani RG, Gannon J, Self M, Rich PA. L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. International journal of sport nutrition and exercise metabolism. 2000;10(2):199-207.

9.       Walter P, Schaffhauser AO. L-Carnitine, a 'Vitamin-like Substance' for functional food. Proceedings Of the symposium on L-carnitine, april 28 to may 1, 2000, zermatt, switzerland. Annals of nutrition & metabolism. 2000;44(2):75-96.

10.   Obici S, Feng Z, Arduini A, Conti R, Rossetti L. Inhibition of hypothalamic carnitine palmitoyltransferase-1 decreases food intake and glucose production. Nature medicine. 2003;9(6):756-61.

11.   Karlic H, Lohninger S, Koeck T, Lohninger A. Dietary l-carnitine stimulates carnitine acyltransferases in the liver of aged rats. The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society. 2002;50(2):205-12.

12.   Malaguarnera M, Gargante MP, Russo C, Antic T, Vacante M, Malaguarnera M, et al. L-carnitine supplementation to diet: a new tool in treatment of nonalcoholic steatohepatitis--a randomized and controlled clinical trial. The American journal of gastroenterology. 2010;105(6):1338-45.

13.   Karlic H, Lohninger A. Supplementation of L-carnitine in athletes: does it make sense? Nutrition. 2004;20(7-8):709-15.

14.   Brass EP, Hiatt WR. The role of carnitine and carnitine supplementation during exercise in man and in individuals with special needs. Journal of the American College of Nutrition. 1998;17(3):207-15.

  • Is L-Carnitine Effective On Weight Loss and Exercise Recovery?


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