When researchers first discovered carnitine in 1905, naming it for the meat — or carnus — in which it was found, little could they have known the far-ranging benefits it would have for athletes. Now, of course, we know its essential role in energy production, helping transform fat into energy, and its positive weight-loss effects. As an added bonus, it functions as an antioxidant, fighting off electron-stealing free radicals, thereby reducing DNA damage to healthy cells. In the world of sports supplementation, it can be considered a multi-tool player, capable of making a huge difference in your game, whether your goals are on the court or on the scale.
Carnitine: The Facts
A naturally occurring nutrient, carnitine is synthesized in the liver and kidneys and stored mainly in tissues that rely on fatty acids for energy, such as skeletal and heart muscle. Although it can be synthesized in the human body from the amino acids lysine and methionine, it’s considered conditionally essential — meaning some dietary carnitine is necessary — because the body’s demands for carnitine can exceed its ability to produce it.
The best dietary source of carnitine is red meat like beef, but it is also found in dairy, poultry, fish, peanut butter, avocados and wheat. In dietary supplements, carnitine is available in a few different forms: L-carnitine, L-carnitine L-tartrate, acetyl-L-carnitine and propionyl-L-carnitine. Only the L isomer of carnitine is known to have biological activity, so D-carnitine supplements are not recommended because they can interfere with L-carnitine absorption and may actually cause carnitine deficiency.
The first law of thermodynamics is that energy can neither be created nor destroyed. It can be converted, though, and L-carnitine is absolutely essential for changing fat into energy when the body needs it.
According to information from the Linus Pauling Institute, before fatty acids can be used for energy, they have to be in their activated form, acylcarnitine. So L-carnitine generates the acylcarnitines, which can then gain entrance into the inner mitochondrial matrix. They get there by tagging along with a protein known by the acronym CACT, or by the clunky scientific name, carnitine-acylcarnitine translocase. Once inside the matrix, the activated fatty acids undergo a metabolic process called beta-oxidation, which ends in the creation of two new compounds, propionyl-coenzymeA (CoA) and acetyl-CoA. Acetyl-CoA, then, is oxidized to create ATP — adenosine triphosphate — otherwise known as cellular energy. Long story short, L-carnitine helps get fatty acids into the body’s energy-producing cells, the mitochondria, for metabolism.
Because of its roles in producing acylcarnitines and enhancing fatty-acid oxidation, among other things, the theory is that taking carnitine can improve exercise performance. A report in the August 2000 American Journal of Clinical Nutrition indicated that carnitine supplementation can improve responses to training as well as reduce muscle fatigue. What’s more, combining carnitine with antioxidant supplements can boost carnitine metabolism, which subsequently supports athletic performance.
Additional evidence shows that L-carnitine supplements are beneficial for training, competition and recovery. An overview of carnitine research appearing in a 2004 issue of Nutrition indicates that carnitine likely elicits ergogenic effects by increasing maximal oxygen consumption and stimulating fat metabolism, not to mention decreasing post-exercise plasma lactate. The report also noted that L-carnitine supplements can speed post-exercise recovery by preventing cellular damage.
Glycine propionyl-L-carnitine is another form of carnitine known to reduce lactic acid in resistance training. In fact, according to researchers reporting in a 2009 issue of the Journal of the International Society of Sports Nutrition, taking 4.5 grams of the supplement 90 minutes before training enhances peak power with significantly less lactic-acid production.
Several studies of L-carnitine L-tartrate (LCLT) have shown that this form of carnitine reduces post-exercise hypoxic stress. One 2008 report in Journal of Strength and Conditioning Research showed that LCLT enhanced oxygen consumption and reduced hypoxic stress in men who took 2 grams per day for 23 days. Another study, appearing in a 2009 issue of Metabolism, showed that LCLT reduced free-radical formation and post-exercise tissue damage, as well as optimized muscle tissue repair and remodeling.
Battle of the Bulge
The evidence for carnitine in the realm of fighting fat isn’t as prevalent as its role in energy production and performance, but it is certainly promising. One study showed that taking 3 grams of L-carnitine for 10 days boosted fat oxidation. What’s more, the 2004 report in Metabolism showed that the study participants didn’t have an increase in protein breakdown at the same time — good for those who want to preserve muscle mass.
Preliminary evidence that supports carnitine for enhancing body composition shows that the nutrient works against fat in a couple of ways. One way is by preventing pre-fat cells from plumping up to full maturity, according to a 2003 report in the Journal of Medicinal Food. Researchers at Chonbuk National University in South Korea cultured immature fat cells called 3T3-L1 preadipocytes with L-carnitine and found that the nutrient prevented the cells from filling with triglycerides and total lipids.
The same researchers reviewed the literature on carnitine and obesity in 2008 and verified these findings in the body of evidence. They also noted that dietary L-carnitine seems to specifically stymie weight gain around the abdomen.
Tried and True
In the realm of performance nutrition, L-carnitine is a natural way to boost the benefits of training and possibly shed some unwanted fat without losing muscle at the same time. The research shows that the naturally occurring nutrient is a must-have for muscles because it turns fat into energy. It also staves off free-radical damage and promotes faster recovery. For athletes seeking a well-studied, multifunctional supplement, L-carnitine is a winner.
Age may be only a number, 30 the new 20 and all that, but the sad fact is that during aging, energy production and cognition become less efficient. One reason for this is that oxidative damage caused by free radicals starts to take its toll on the body’s energy-producing cells, the mitochondria. Taking acetyl-L-carnitine — a popular study subject in neurological disease — may slow these side effects of aging by protecting the mitochondria from free-radical damage.
Preliminary research in animals shows that adding acetyl-L-carnitine to the diet actually restored the old animals’ mitochondrial function to the level of the young animals. By preventing oxidative damage to the mitochondria, acetyl-L-carnitine also may improve brain function: Animal research shows that aged rats fed acetyl-L-carnitine displayed improved memory and cognition. Now that makes carnitine a nutrient to remember when you’re restocking your supplement cache.
Typically, recommended dosage levels of carnitine range from 500 milligrams to 3 grams per day divided into 500- to 1,000-milligram servings; it should be taken with meals.