I am often asked if people who avoid consuming all animal products need to take a supplement of carnitine. What they have been told is that it only comes from animal source, and so those who avoid animal products will have a deficiency of it and this will result in muscle wasting and/or chronic fatigue syndrome.
Is this true?
Of course not.
While the highest concentrations of carnitine are found in red meat and dairy products they are not the only source.
Other natural sources of carnitine include nuts and seeds, legumes, vegetables, fruits, and cereals though the amount is much less than what is in animal products
Healthy individuals, including strict vegetarians, can synthesize enough L-carnitine to prevent deficiency, if they are on a healthy diet and following a healthy lifestyle.
(Again, however, this is not always the case with many vegans and vegetarians).
Healthy people, can maintain carnitine balance through internal synthesis of L-carnitine, absorption of carnitine from dietary sources, and elimination and reabsorption of carnitine by the kidney. Humans synthsize L-carnitine from the amino acids lysine and methionine.
The rate of L-carnitine synthesis has been studied in vegetarians and is estimated to be 1.2 micromol/kg of body weight/day.
Lombard KA, Olson AL, Nelson SE, Rebouche CJ. Carnitine status of lactoovovegetarians and strict vegetarian adults and children. Am J Clin Nutr. 1989;50(2):301-306.
The availability of L-carnitine can vary depending on dietary composition. Onne study reports that bioavailability of L-carnitine in individuals adapted to low-carnitine diets (i.e., vegetarians) is higher than those adapted to high-carnitine diets (i.e., regular red meat eaters; 66%-86% versus 54%-72%)
Rebouche CJ, Chenard CA. Metabolic fate of dietary carnitine in human adults: identification and quantification of urinary and fecal metabolites. J Nutr. 1991;121(4):539-546.
Renal reabsorption of L-carnitine is normally very efficient; in fact, an estimated 95% is thought to be reabsorbed by the kidneys. However, several conditions can decrease carnitine reabsorption efficiency and, correspondingly, increase carnitine excretion. Such conditions include high-fat (low-carbohydrate) diets, high-protein diets, pregnancy, and certain disease states
Even strict vegetarians (vegans) show no signs of carnitine deficiency, despite the fact that most dietary carnitine is derived from animal sources.
The normal rate of L-carnitine biosynthesis in humans ranges from 0.16 to 0.48 mg/kg of body weight/day. Thus, a 70 kg (154 1b) person would synthesize between 11 and 34 mg of carnitine per day. This rate of synthesis combined with efficient (95%) L-carnitine reabsorption by the kidneys is sufficient to prevent deficiency in generally healthy people, including strict vegetarians.
Rebouche CJ. Carnitine. In: Shils ME, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in Health and Disease. 9th ed. Philadelphia: Lippincott, Williams & Wilkins; 1999:505-512.
In addition to the above, there are a few studies on longevity and carnitine in rats, but these are short term studies using very high doses and there is no conclusive evidence in rats yet, let alone humans.