The most important function of carnitine is thought to be its role in regulating fat metabolism – carrying fat across a membrane to the energy-burning mitochondria of each cell. The more carnitine is available, the faster fat is transported, and the more fat is used for energy. This is a particularly vital function in the heart muscle.
Carnitine also helps the body to break down branched-chain amino acids into fuel for the muscles when necessary, and it controls ketone levels in the blood. Ketones are the result of the incomplete oxidation of fats in energy production. They are high in diabetics (whose hearts often metabolize carnitine abnormally) and they also rise in high-protein or high-fat diets and tend to acidify the blood.
In a double-blind study which administered 2 grams of carnitine or a placebo to ten volunteers 1 hour before they began working on an exercise cycle, it was found that at the maximum exercise intensity, treatment with L-carnitine significantly increased the maximum oxygen uptake and power output. Oxygen uptake, carbon dioxide production, pulmonary ventilation and plasma lactate were reduced. The researchers concluded that carnitine supplementation results in a more efficient performance at maximum exercise intensity. (Vecchiet L et al: Influence of L-carnitine administration on maximal physical exercise. Eur J Appl Physiol 61(5-6):486-90, 1990.)