L-carnitine is an amino acid that plays a critical role in the metabolism of fat. This amino acid transports long chain fatty acids into the mitochondria, the key cellular site for energy metabolism. Specifically, l-carnitine carries long chain fatty acids across the mitochondrial membrane. long chain fatty acids can not cross the mitochondrial membrane to get inside the mitochondria in the absence of carnitine. Consequently, only small amounts of fatty acids (from the short and medium chain fatty acids) would be oxidized (burned) in the absence of l-carnitine. Not only is l-carnitine necessary for the oxidation of significant amounts of fatty acids, it is also the rate-limiting step in the burning of these fatty acids. The critical role of l-carnitine in fat metabolism has notable implications for aerobic fitness and body fat reduction.
L-carnitine is a non-essential amino acid that can be produced in your body from lysine and methionine. Lysine and methionine, however, are essential amino acids, and they must be obtained from your diet or supplements. L-carnitine is produced by your liver and kidneys and stored largely in the muscles. Your body does not always produce enough l-carnitine, and deficiency can occur. Additionally, the body's stores of l-carnitine tends to decline as we age. Its deficiency can also occur if your diet is poor in lysine and methionine, the essential amino acids that your body needs for synthesizing l-carnitine.
Metabolism of Fatty Acids in the Mitochondria
Fatty acids are oxidized in the mitochondria by a process called beta oxidation. In this process, two carbon units at a time are chopped off the fatty acid chain and burned. This beta oxidation occurs very quickly as long as fatty acids are available in the mitochondria. The availability of fatty acids in the mitochondria is determined by the rate at which l-carnitine delivers them into the mitochondira. This is why the transport of fatty acids into the mitochondria is called the rate-limiting step in the oxidation (burning) of fats.
Aerobic fitness may be loosely defined as the ability to perform aerobic activity (such as jogging) at a moderate intensity for a prolonged period. When you perform aerobic activity at a moderate intensity (eg., applying 50 to 75 per cent of your maximal effort), then fat would be the primary source of energy if you are aerobically fit. Adequate supply of oxygen and fatty acids are critical for supporting stamina and aerobic fitness. If adequate transport activity of l-carnitine is present, then you have met one of the key factors needed for stamina and aerobic fitness.
Body Fat Reduction
Body fat reduction is accelerated by the simultaneous increases in fat burning and appetite suppression. The mechanism by which l-carnitine curbs the appetite is not fully understood. One likely explanation is that l-carnitine tends to increase the utilization of fat for energy metabolism by the muscles, the biggest energy users in your body. Stored glucose would be conserved if the muscles use fat as the primary source of energy. This in turn would tend to prevent plasma glucose from declining sharply and activating the hunger mechanism.
Sources of L-Carnitine
Your body can typically produce about 80 percent of the l-carnitine that your body needs. The rest must come from nutritional sources. Additionally, your body's ability to produce l-carnitine can be impaired if your diet is deficient in lysine and methionine, the precursors of l-carnitine. L-carnitine is found largely in animal sources. Some sources of l-carnitine are: beef, pork, chicken, cod, avocado and peanuts. Lysine is found in significant amounts in meats and beans. Some nutritional source of lysine are lamb, pork, poultry, cheese, soy beans, kidney beans and lentils. Some nutritional sources of methionine are meats, fish, some nuts and eggs.