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Lee Swanson Research Update
Carnitine Transporter May Adapt to Lower Levels in Vegetarians
August 2011
New research coming out of the United Kingdom says vegetarians have a reduced capacity to transport carnitine into muscle and store it, even though they do not excrete as much as non-vegetarians.
Carnitine plays an essential role in fat and carbohydrate metabolism. It is found mainly in foods of animal origin, and over 95% of the human body’s total carnitine is stored in skeleton muscle tissue.
Researchers from Nottingham University Medical School in the UK set out to test the hypothesis that muscle carnitine uptake and retention are higher in vegetarians than in meat eaters.
While they found that vegetarians excreted less carnitine than non-vegetarians, they had lower concentrations in their blood and muscles, as well as lower levels of the transporter messenger and protein expressions. Uptake was also seen to be lower in vegetarians.
The lower storage levels of carnitine in muscles may be due to lower presence of the muscle carnitine transporter, organic cation transporter 2 (OCTN2), which the researchers propose adapts to lower stores and retains some of the nutrient for other tissues.
The findings could have implications for people on long-term carnitine-free parentenal (intravenous) nutrition, or people on hemodialysis who are carnitine deficient.
Dr. Kevin Owen, NAFTA Head of Technical Marketing and Scientific Affairs at Lonza, which supplied its L-carnitine for the study (L-carnitine is the biologically active stereoisomer of carnitine), said: "The results of this study confirm Lonza’s position that vegetarians can benefit by adding supplemental L-carnitine to their diets. A good supply is important for active people providing the energy they need."
"After heavy exercise, vegetarians may get a functional L-carnitine deficiency, meaning that there is a lack of available, free L-carnitine in the cell."
The research team recruited 17 healthy vegetarian and 22 healthy non-vegetarian participants with an average age of 22 years. The volunteers took part in two studies.
In the first study 11 vegetarians (seven men and four women) and 14 male non-vegetarians (who ate red meat on average twice a week) received intravenous L-carnitine and an infusion of insulin to stimulate take-up over five hours, on two separate laboratory visits.
In the second study eight men who had been vegetarians for between eight and 14 years and eight non-vegetarians were given 4.5 g of L-carnitine L-tartrate to ingest, dissolved in 200 mL of water. They were asked to collect their urine for 24 hours.
Greater whole-body carnitine retention in vegetarians was observed after a single dose of L-carnitine, as their 24-hour total carnitine urine excretion was 58% lower. However, the basal plasma total carnitine concentrations were 16% lower in the vegetarians than in the non-vegetarians, muscle total carnitine content was 33% lower, and muscle carnitine transporter messenger RNA and protein expressions were 37% lower.
The non-vegetarians also had a 15% increase in muscle total carnitine when receiving L-carnitine with hyperinsulinemia, while in the vegetarians the L-carnitine had no effect on total carnitine, with or without hyperinsulinemia.
American Journal of Clinical Nutrition; Published online ahead of print.
