mehr Info
Supplement Carnitine
Description Carnitine is an amino acid that is synthesized in the liver and kidneys from lysine and methionine. The major function of carnitine is to facilitate the transport and metabolism of long-chain fatty acids into the mitochondria for beta-oxidation and energy generation. Carnitine can be also found in the diet in foods such as meat and dairy products.
Claims
Enhanced endurance
Increased fat metabolism
Lowers cholesterol & triglyceride levels
Cardioprotective
Theory
Carnitine supplementation could potentially be beneficial under several conditions. First, because of carnitine’s role in facilitating fatty acid transport into the mitochondria for oxidation, it is possible that elevated carnitine levels would permit a greater/faster transport of fat leading to increased fat oxidation, which may impact weight loss and/or endurance performance. A greater reliance on fat for energy may also result in a sparing of muscle glycogen and a subsequent enhancement of exercise performance. It is also theoretical that supplemental carnitine could have some effect on reducing lactic acid accumulation in muscles by buffering pyruvate and, therefore, extending exercise capacity before fatigue.
Scientific Support
Studies of the role of carnitine as an ergogenic aid have been equivocal, with several suggesting a beneficial effect of supplements and other indicating no effect at all. Several early studies suggested an indirect effect of carnitine (2 to 6 g/day) on endurance performance by showing a reduction in the respiratory exchange ratio (RER), which indicates a greater reliance on fats for energy generation. Other studies have failed to indicate any glycogen sparing effect of carnitine supplements (6 g/day). It has also been shown that with supplements, although blood carnitine levels go up, the acyl-enzyme system for fatty acid transport into the mitochondria is not augmented – suggesting that the body does a pretty good job of "packing" enough carnitine into the mitochondrial membrane without the help of dietary supplements
In terms of weight loss, the very low calorie diets (less than 500 calories per day) that are used for intensive obesity treatment have been shown to result in lower levels of carnitine in the blood and tissues – possibly due to an increase in carnitine excretion of or other aspect of carnitine metabolism. Because carnitine transports fatty acids into mitochondria for oxidation, any reduction in carnitine status in peopletrying to lose weight may be viewed as detrimental. A double-blind investigation tested the weight loss effects of carnitine in 36 moderately overweight premenopausal women (18 received 4 grams of carnitine per day and 18 received placebo) for 2 months. Subjects also completed 30 minutes of walking exercise (60-70% of maximum heart rate) 4 days/week. Results indicated no significant changes in body weight, fat mass, or the amount of fat oxidation at either rest or during exercise- suggesting that carnitine may not be particularly effective for promoting weight loss.
In support of the beneficial role of carnitine supplements, however, are studies in kidney dialysis patients showing that low carnitine levels in the dialysate can lead to elevated levels of blood lipids. Likewise, studies of heart disease patients have shown that carnitine supplements (2g/ day over 6 months) can reduce cholesterol and triglyceride levels. Perhaps the most convincing data on the benefits of carnitine as a dietary supplement come from several studies of patients with heart disease. Among individuals who had suffered a heart attack, carnitine supplements (2-3 g/day over 4-8 weeks) resulted in a reduction in the amount of damage to the heart muscle and an increase in heart muscle viability. Among those suffering from angina (pain in the chest), carnitine reduces the incidence of angina and cardiac arrythmias as well as reduces the need for anti-angina and anti-arrythmic medications. In addition, carnitine (2g/ day for 6 months) can also increase exercise tolerance in patients with angina – meaning that they can exercise longer and at a higher level before experiencing chest pain.
These data suggest that although the ergogenic benefits of carnitine supplements are probably unfounded, or at least hard to measure, the benefits in terms of heart function and blood lipid maintenance are interesting. Under conditions in which the heart muscle is deprived of oxygen (i.e. heart attack and angina), fat breakdown and energy production are reduced. It also appears that carnitine concentrations may be somewhat reduced in cardiac cells undergoing such stress. Supplemental levels of carnitine may help replenish the lost carnitine and facilitate a return to adequate levels of fatty acid transport and energy production in the heart muscle.
Safety
Doses of 2-6 grams per day over a period of 6 months have been studied with no observed adverse side effects.
Value
For athletes, as an ergogenic aid – not recommended except for vegetarians who may not consume adequate levels of carnitine or its precursor amino acids (lysine and methionine) in their diets
For cardioprotecive benefits – recommended as a daily supplement to help maintain blood lipid profile and promote fatty acid utilization within heart muscle.
It is important to note that some supplemental forms of carnitine actually contain the physiologically inactive form of carnitine (D-carnitine) rather than the form which is active in humans (L-carnitine). Over-saturation of the tissue with the "D-" form could possibly displace the active form of carnitine in tissues and lead to muscle weakness.
Dosage
Doses of 2 to 6 grams per day are typically recommended for cardiovascular, sports performance and weight loss benefits – although the effectiveness of any dose of carnitine for sports or weight loss effects are not impressive. As a “heart health” nutrient, approximately 2 grams per day of carnitine may provide some benefits in terms of promoting general heart function.
References
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11. Villani RG, Gannon J, Self M, Rich PA. L-Carnitine supplementation combined with aerobic training does not promote weight loss in moderately obese women. Int J Sport Nutr Exerc Metab. 2000 Jun;10(2):199-207.
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