Carnitine has long been known as the "fat burning" supplement. Recent studies, however, suggest that there's a lot more to carnitine than the crucial role it plays in helping athletes get and stay lean. Carnitine is a nutrient that accumulates in cells where it helps transport fat into the mitochondria to be burned. Since carnitine is natural, non-toxic, and deficiencies have been linked to profound impairment in muscle function, there is little downside--and plenty of upside--to considering this supplement in your nutritional arsenal, especially when you consider the exciting science that has been done in the last few years.
Without carnitine, fats cannot be burned for energy. This explains the fascination with carnitine supplementation as a fat burner. In two separate studies, supplementation of carnitine (3 grams per day) for 10 days resulted in significantly higher rates of fat oxidation (1,2). This work was recently validated by researchers in the United Kingdom (3). They studied healthy endurance-trained men who supplemented with 80 grams of carbohydrate 2 times per day for 24 weeks. One group also received 2 grams l-carnitine l-tartrate (LCLT) 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. Work output was 35% greater than controls.
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Several lines of evidence support a role of carnitine in other processes beyond muscle fat burning. Much of this work has been done over the last decade in my laboratory at the University of Connecticut. Building on prior work that had showed carnitine had anti-oxidant and vaso-active (promotes dilation) effects, we conducted a series of studies aimed at elucidating the role of LCLT in exercise recovery.
In our first study we reported that healthy men who supplemented with LCLT (2 g/day for 3 wks) showed significantly less accumulation of markers of post-exercise stress including less formation of free radicals, tissue damage, and muscle soreness after moderate intensity squat exercise (4). We performed a follow-up study to validate those findings and determine whether a smaller dose of LCLT was effective (5). Healthy men performed a resistance exercise challenge that included 5 sets of squat exercise on 3 separate occasions. For 3 weeks prior to each test, subjects ingested either 1 gram LCLT/day, 2 g LCLT/day, or a placebo. Similar to our previous work we showed that LCLT supplementation was effective at reducing the acute response of several markers of biochemical stress after resistance exercise. In addition, perception of muscle soreness was lower after exercise. A novel finding was that 1 g/day LCLT was as effective as 2 g/day. Since our prior work was in young men, we performed a third experiment in middle-aged men and women 40-65 years of age (6). We used a similar methodology and LCLT dose (2 grams per day). Similar to the previous two studies, we validated that LCLT supplementation lowered post-exercise markers of metabolic stress, muscle disruption, and muscle soreness in baby boomers.
There are several lines of evidence pointing to a possible role of carnitine in testosterone metabolism so we performed another study to examine the influence of LCLT on testosterone responses to resistance exercise. Resistance exercise is a reliable stimulus for transiently increasing testosterone, but one of the puzzling issues is that ingesting calories after exercise consistently reduces the testosterone response. Testosterone can bind to almost any cell in the body so simply increasing testosterone levels will not necessarily result in anabolic effects in muscle unless the hormone actually binds to androgen receptors on muscle. So we thought that ingesting calories after exercise would increase androgen receptors on muscle explaining why blood levels of testosterone were lower and that LCLT might play a role as well. Indeed we showed that feeding after exercise decreased the testosterone response but that androgen receptors in muscle were upregulated. Further we showed that 3 weeks of LCLT supplementation increased resting androgen receptor content (7).
Carnitine has other benefits on overall health. A large number of studies have shown that carnitine has vasoactive effects improving the ability of blood vessels to dilate. In another experiment, we set out to examine the effects of carnitine supplementation on flow mediated dilation of the brachial artery as a measure of vascular health (8). Healthy subjects consumed a high fat meal which has been shown to cause impairment of vascular health. We showed that ingestion of 2 grams LCLT with the meal enhanced vascular responses (increased dilation) to the high fat meal. This was most apparent in those subjects who had the greatest decrease in vascular function. Because vascular dysfunction is an early event in heart disease, this finding is of considerable interest and worthy of further study.
In addition to potentially enhancing fat burning at rest and during exercise, carnitine supplementation enhances recovery from exercise, decreases exercise-induced muscle damage, decreases muscle soreness, increases anti-oxidant effects, enhances androgen receptors, and improves vascular function. An innovative product that incorporates LCLT is AndroCept from BioQuest. It contains the same dose of LCLT used in all our prior work with additional co-factors.
1. Wutzke KD, Lorenz H. The effect of l-carnitine on fat oxidation, protein turnover, and body composition in slightly overweight subjects. Metabolism. 2004 Aug;53(8):1002-6.
2. Müller DM, Seim H, Kiess W, Löster H, Richter T. Effects of oral L-carnitine supplementation on in vivo long-chain fatty acid oxidation in healthy adults. Metabolism. 2002 Nov;51(11):1389-91.
3. 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.
4. Volek, J. S., Kraemer, W. J., Rubin, M. R., Gomez, A. L., Ratamess, N. A. & Gaynor, P. L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress. Am J Physiol Endocrinol Metab. (2002); 282:E474-482.
5. Spiering, B. A., Kraemer, W. J., Vingren, J. L., Hatfield, D. L., Fragala, M. S., Ho, J. Y., Maresh, C. M., Anderson, J. M. & Volek, J. S. Responses of criterion variables to different supplemental doses of L-carnitine L-tartrate. J Strength Cond Res. (2007); 21:259-264.
6. Ho JY, Kraemer WJ, Volek JS, Fragala MS, Thomas GA, Dunn-Lewis C, Coday M, Häkkinen K, Maresh CM. l-Carnitine l-tartrate supplementation favorably affects biochemical markers of recovery from physical exertion in middle-aged men and women. Metabolism. 2010 Aug;59(8):1190-9.
7. Kraemer WJ, Spiering BA, Volek JS, Ratamess NA, Sharman MJ, Rubin MR, French DN, Silvestre R, Hatfield DL, Van Heest JL, Vingren JL, Judelson DA, Deschenes MR, Maresh CM. Androgenic responses to resistance exercise: effects of feeding and L-carnitine. Med Sci Sports Exerc. 2006 Jul;38(7):1288-96. Erratum in: Med Sci Sports Exerc. 2006 Oct;38(10):1861.
8. Volek JS, Judelson DA, Silvestre R, Yamamoto LM, Spiering BA, Hatfield DL, Vingren JL, Quann EE, Anderson JM, Maresh CM, Kraemer WJ. Effects of carnitine supplementation on flow-mediated dilation and vascular inflammatory responses to a high-fat meal in healthy young adults. Am J Cardiol. 2008 Nov 15;102(10):1413-7.