Carnitine, typically in the form of L-carnitine, has developed a following as a supplement for those wanting to increase muscle strength and energy, and to burn fat more efficiently. However, research is showing it may provide benefits to a much wider population swath. Studies are uncovering that L-carnitine can promote cardiovascular health and that it may prove useful in the fight against obesity.

Things chemical and biochemical

The name carnitine encompasses a group of compounds that include L-carnitine, acetyl-L-carnitine, propionyl-L-carnitine and L-carnitine L-tartrate. Carnitine (C7 H16 NO3+ ), whose precursors are the amino acids lysine and methionine, has two isomers, D and L, but only the form found in food, L-carnitine, is active in the body. It is essential in the body’s metabolic processes, playing a role in a host of metabolic pathways, including:

• Fatty-acid transport: On a cellular level, carnitine moves medium- and long-chain fatty acids across the mitochondrial membrane, so they can be metabolized into energy.

• Toxin removal: Carnitine helps transport toxins out of the mitochondria, preventing accumulation.

• Coenzyme A (CoA) buffer: Carnitine helps maintain an adequate level of free CoA by reacting with the acyl groups of acylCoA.

• Membrane repair: Carnitine might provide activated fatty acids to enzymes that remove and replace damaged fatty acids from membrane phospholipids.

Consuming carnitine

Average diets containing red meat and other animal products, including whey, provide about 60 to 180 milligrams of carnitine per day. Vegetarians consume much less, about 10 to 12 milligrams daily. Carnitine is absorbed in the intestine, with the rate depending on the dose and dietary source: 54% to 87% is absorbed from food and 14% to 18% from supplements. Daily intake over 3 grams may cause unpleasant side effects, such as nausea and abdominal cramps. The body concentrates carnitine in areas that use fatty acids as fuel, such as the skeleton and cardiac muscle. In a 155-lb. man, the total body content of carnitine is about 20 grams.

In general, the body synthesizes sufficient carnitine from lysine- and methionine-containing proteins to meet its needs. The Food and Nutrition Board of the National Academy of Sciences has concluded it’s not an essential nutrient for the general population, so no Dietary Reference Intakes (DRIs) or recommended dietary allowance (RDA) exist. However, some individuals, such as preterm infants, lack the ability to make enough, and require carnitine as a conditionally essential nutrient.

A popular book, “The Carnitine Miracle,” by Robert Crayhon, M.S., calls it a “supernutrient,” and while that might be a touch of hyperbole, science is discovering it may provide benefits in many areas. The most common use for carnitine is by physically active people as a post-exercise recovery aid. In addition, some athletes take carnitine to improve performance, although current research has not verified this effect in healthy people.

Because of carnitine’s role in fatty-acid transport, it could increase fat oxidation, which might enhance weight loss and endurance performance. Some theorize that supplemental carnitine may help reduce muscle’s lactic acid accumulation, increasing the time before fatigue sets in. L-carnitine has been suggested as a beneficial nutrient for those suffering from cardiovascular disease, type 2 diabetes, Alzheimer’s disease and HIV, but these benefits require further research. Also, animal studies suggest acetyl-L-carnitine may help prevent age-related declines in energy and memory.

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