Carnitine (derived from the Latin carnus, or flesh) is a water-soluble, conditionally-essential nutrient that is reinventing itself as a performance enhancer. First discovered over 100 years ago by Russian scientists, carnitine is synthesised in the liver and kidneys from the essential amino acids lysine and methionine. Like its muscle-building cousin creatine, approximately 95% of our total carnitine stores are found in skeletal muscle, and for most humans, the main dietary source is red meat (Table 1). In contrast to the fatigue-fighting pre-workout supplement beta-alanine which buffers changes in muscle pH that would otherwise lead to decrements in power output, carnitine is a post-workout supplement that works through entirely different mechanisms (e.g. ferrying fatty acids into the mitochondria, increasing mitochondrial ATP resynthesis at the onset of intense exercise, and protecting cell membranes from the damaging effects of free radical accumulation).
The initial interest in carnitine stemmed from the observation that its main metabolic function was to assist in burning bodyfat. More specifically, L-carnitine is required for the transport of long-chain fatty acids into the mitochondria where they can be chopped up and burned by a process called beta-oxidation (Figure 1, below). Logically then, eating more carnitine means your body can burn more fat, right? Not exactly. First, the bioavailability of carnitine supplements in humans is dreadful, averaging 5-20% at best. Second, as mentioned previously, since 95% of our carnitine already resides in skeletal muscle, increasing muscle levels any further is like pushing a truck uphill. That is, the concentration gradient is quite steep and difficult to overcome. So not surprisingly, initial studies showed no benefits of L-carnitine supplementation on exercise metabolism, oxygen uptake, muscle carnitine concentrations or weight loss.
Recently, a few savvy exercise and nutrition scientists have discovered an ingenious way to increase carnitine delivery to muscle. As a result, new studies are uncovering the ability of this novel nutrient to reduce resistance exercise-induced muscle tissue damage and soreness, improve blood flow, decrease markers of oxidative stress, increase muscle androgen (testosterone) receptor content, and enhance exercise work output and recovery.
In addition, fat oxidation and aerobic performance can be increased, but only when 2 grams of L-carnitine L-tartrate are chronically co-consumed (twice daily) with 80 grams of a unique, high-molecular weight, low-osmolality carbohydrate called Vitargo®. The carnitine group in this latter study burned 55% less glycogen when cycling at lower intensity (50% VO2 max), had 44% less lactate accumulation when exercising at higher intensity (80% VO2 max), and improved their performance by 11% during an all-out 30 minute exercise test.
Since 2003, researchers from the University of Connecticut have performed several unique studies examining the potential interaction of L-carnitine L-tartrate supplementation and resistance training. One of their most interesting findings was that men taking 2 g/day for three weeks noted significant increases in muscle androgen receptors. Increased androgen receptor content is thought to enhance the uptake of testosterone into muscle, thus promoting muscle growth. Earlier work from the same laboratory reported that L-carnitine L-tartrate supplementation resulted in less muscle damage (confirmed via blood samples and magnetic resonance images) in men and women performing repeated sets of back squats. As a result of these and other studies, many hard-training athletes now include several grams of carnitine as part of their daily post-workout supplementation plan.
OTHER BENEFITS OF CARNITINE
Carnitine is also concentrated in heart muscle, which uses fatty acids as its primary fuel source. As a result, several convincing studies have shown that carnitine supplementation can reduce chest pain (angina) in cardiovascular patients, both at rest and during mild physical exertion. In addition, other research on carnitine has reported improvements in male fertility, enhanced cognitive function in the elderly, and most recently, a decrease in lymphocyte apoptosis, which may slow the progression of HIV infection.
At the end of the day, supplementing with carnitine won’t turn a 98-pound weakling into a professional bodybuilder. Nor will it allow you to compete with Lance Armstrong in the Tour de France. But given its bevy of wide- ranging benefits, it might just help you perform and look your best. M&F
Carnitine At A Glance
- Carnitine is a generic term that usually refers to L-carnitine, acetyl-L-carnitine or propionyl-L-carnitine.
- Foods rich in carnitine include red meat, pork and tempeh.
- Carnitine has been well studied for its ability to transport long-chain fatty acids into the mitochondria of the cell where they are burned for energy.
- Although carnitine is not a fat-burner per se, it does have powerful effects on enhancing muscle recovery from intense exercise.
- Recent research has demonstrated that carnitine can reduce muscle damage, decrease muscle soreness, and (when co-ingested with carbohydrates) enhance muscle glycogen levels and increase fat oxidation.
- To reap these benefits from carnitine, doses of two to four grams per day should be ingested, in divided doses, always with an insulinogenic and/or post-workout meal.
- In humans, L-carnitine L-tartrate is the form most studied for performance enhancement and recovery; acetyl-L-carnitine crosses the blood-brain-barrier and is the form most studied in Alzheimers and dementia; and propionyl-L-carnitine is the form most studied for heart disease and peripheral vascular disease.
Figure 1. The role of carnitine in fatty acid transport from the cytoplasm (cytosol) to the mitochondria (matrix).
For more specific recommendations on the use of carnitine and other dietary supplements, athletes are encouraged to seek the guidance of a Certified Sports Nutritionist (CISSN) from the International Society of Sports Nutrition (www.sportsnutritionsociety.org).
Dr. Tim Ziegenfuss is past president of the International Society of Sports Nutrition and CEO of the Center for Applied Health Sciences.
References and Recommended Reading:
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Bloomer RJ, Smith WA. Oxidative stress in response to aerobic and anaerobic power testing: influence of exercise training and carnitine supplementation. Res Sports Med. 2009 Jan-Mar;17(1):1-16
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Jacobs PL, Goldstein ER. Long-term glycine propionyl-l-carnitine supplemention and paradoxical effects on repeated anaerobic sprint performance. J Int Soc Sports Nutr. 2010 Oct 28;7:35
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Linus Pauling Institute, Micronutrient Information Center: http://lpi.oregonstate.edu/infocenter/othernuts/carnitine/
Panjwani U, Thakur L, Anand JP, Singh SN, Amitabh, Singh SB, Banerjee PK. Effect of L-carnitine supplementation on endurance exercise in normobaric/normoxic and hypobaric/hypoxic conditions. Wilderness Environ Med. 2007 Fall;18(3):169-76
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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
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