RE-EXAMINING THE ROLE OF CARNITINE IN FAT BURNING
By Jeff Volek - Chat with Doug on the
ProSource Fitness Forum
Feb 2, 2011
is an essential nutrient that participates in transporting fatty acids across the mitochondrial membrane where it is burned as fuel.
Therefore, carnitine supplementation has been marketed as a 'fat burner'. However excitement for this effect has fizzled over the last couple decades because of a failure to show that
actually increases muscle carnitine. Researchers in the United Kingdom have shown in a series of studies that it is possible to elevate muscle carnitine when blood levels of carnitine and insulin are simultaneously elevated. In their most recent work, they had healthy endurance-trained men supplement with 80 g of carbohydrate 2 times per day for 24 weeks. One group also received 2 grams L-carnitine L-tartrate in their carbohydrate beverage. Resting muscle carnitine was unchanged after 12 weeks but increased by 21% after 24 weeks in the carnitine group. When the carnitine group exercised at a low intensity after 24 weeks of supplementation, they showed the higher muscle carnitine was linked to significant muscle glycogen sparing (55% less) compared to controls. Furthermore, several other measures of energy status were better with carnitine supplementation, and work output was 35% greater than controls. These interesting findings point to the need to reconsider the role of carnitine supplementation in enhancing muscle energetics, fat burning, and performance. A major drawback to the approach of increasing muscle carnitine is the simultaneous ingestion of high amounts of carbohydrate that stimulate insulin, a potent inhibitor of fat breakdown and fat oxidation. Identification of strategies to increase muscle carnitine that do not involve stimulating insulin would be a major breakthrough.
Wall BT, Stephens FB, Constantin-Teodosiu D, Marimuthu K, Macdonald IA, Greenhaff PL. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans: the dual role of muscle carnitine in exercise metabolism. J Physiol. 2011 Jan 4. [Epub ahead of print]
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