Two studies on L-carnitine highlight new questions regarding the nutrient and vegetarian needs.
Vegetarians have reduced total carnitine levels and reduced capacity to transport carnitine to the muscles, according to new research out of the University of Nottingham’s Institute of Clinical Research.
L-carnitine is an amino acid considered critical to the human process of energy metabolism. Since it is primarily found in meat sources in the omnivorous diet, vegetarians receive only negligible amounts of dietary L-carnitine and must rely on natural stores within the body and endogenous synthesis. For this reason, the researchers questioned whether vegetarians might have an increased ability to retain carnitine in the skeletal muscles-where about 95% of total carnitine is believed to reside-and an increased ability to transport carnitine throughout the body.
Researchers performed two tests on 41 subjects (17 lacto-ovo-vegetarians and 22 omnivores). In one study, subjects were assigned to five-hour intravenous infusion of L-carnitine; in a second study, subjects were assigned to one oral dose of 4.5 g L-carnitine L-tartrate.
Compared to nonvegetarians, vegetarians demonstrated significantly reduced skeletal muscle carnitine along with significantly reduced ability to transfer carnitine to the muscles. The researchers assumed that this could be due to lower presence of carnitine transporter OCTN2 and protein expression, which were 33% and 37% lower in vegetarians, respectively.
Still, single-dose supplementation of L-carnitine did produce greater whole-body carnitine retention in vegetarians. The researchers considered that this could mean that more carnitine was being directed to other tissues in the body.
Lead researcher Francis B. Stephens explained the potential implications of his team’s findings:
These findings could have important implications for patients on long-term carnitine-free parenteral nutrition or hemodialysis treatment who become carnitine deficient over time…However, whether reduced muscle carnitine content in vegetarian volunteers has an effect on physiologic functions requires additional investigation, particularly because the muscle carnitine availability is rate limiting for fat oxidation and carbohydrate flux during exercise.
Lonza (Basel, Switzerland) provided L-carnitine supplementation for the study.