L-carnitine is a naturally occurring derivative of the amino acid carnitine, which plays a vital role in the metabolism of fat. It functions as a transporter of fatty acids into the mitochondria, the powerhouse of the cell. It is produced by the liver and kidneys, which send 98 percent of it to be stored in the muscle tissue.
How L-Carnitine Works
L-carnitine helps your body burn fat during exercise by easing the passage of long chain fatty acids through the mitochondrial walls. After the first five minutes of exercise, glycogen supplies of your body are exhausted, and your body turns toward your fat stores for energy. How efficiently your body uses these fat stores determines your endurance. L-carnitine increases this efficiency, thus increasing your energy levels for long-term aerobic activity.
Where It Comes From
Your body synthesizes some of the L-carnitine you need, but most of it comes from exogenous sources such as red meat, dairy products, tempeh, fish, peanut butter, wheat and avocado.
What It's Used For
In a study published in the July 1984 issue of "Japanese Heart Journal," researchers found that L-carnitine improved exercise tolerance in angina patients who used it in addition to the conventional treatment of stable angina. According to research in the 2003 issue of "Current Medical Research and Opinion," acetyl-L-carnitine can increase attention span in Alzheimer's disease. Propionyl L-carnitine, a derivative of L-carnitine, increased walking distances in patients with peripheral arterial disease.
L-carnitine has also been touted as a supplement for weight loss, improving exercise tolerance and overcoming fatigue. Limited information is available on the validity of these claims. A study in the March 2005 issue of "International Journal for Vitamin and Nutrition Research" noted that L-carnitine actually increased tendency for weight gain in female rats.
If you have hypertension, peripheral arterial disease, alcohol liver disease, diabetes or kidney disease, you should take L-carnitine supplementation only under medical supervision. The same goes for people taking any long-term medications.
D-carnitine supplements interfere with the body's L-carnitine levels and are harmful to your health.