Vegetarians have a reduced skeletal muscle carnitine transport capacity

Am J Clin Nutr. 2011 Sep;94(3):938-44. doi: 10.3945/ajcn.111.012047. Epub 2011 Jul 13.


Background: Ninety-five percent of the body carnitine pool resides in skeletal muscle where it plays a vital role in fuel metabolism. However, vegetarians obtain negligible amounts of carnitine from their diet.

Objective: We tested the hypothesis that muscle carnitine uptake is elevated in vegetarians compared with that in nonvegetarians to maintain a normal tissue carnitine content.

Design: Forty-one young (aged ≈22 y) vegetarian and nonvegetarian volunteers participated in 2 studies. The first study consisted of a 5-h intravenous infusion of l-carnitine while circulating insulin was maintained at a physiologically high concentration (≈170 mU/L; to stimulate muscle carnitine uptake) or at a fasting concentration (≈6 mU/L). The second study consisted of oral ingestion of 3 g l-carnitine.

Results: Basal plasma total carnitine (TC) concentration, 24-h urinary TC excretion, muscle TC content, and muscle carnitine transporter [organic cation transporter 2 (OCTN2)] messenger RNA and protein expressions were 16% (P < 0.01), 58% (P < 0.01), 17% (P < 0.05), 33% (P < 0.05), and 37% (P = 0.09) lower, respectively, in vegetarian volunteers. However, although nonvegetarians showed a 15% increase (P < 0.05) in muscle TC during l-carnitine infusion with hyperinsulinemia, l-carnitine infusion in the presence or absence of hyperinsulinemia had no effect on muscle TC content in vegetarians. Nevertheless, 24-h urinary TC excretion was 55% less in vegetarians after l-carnitine ingestion.

Conclusions: Vegetarians have a lower muscle TC and reduced capacity to transport carnitine into muscle than do nonvegetarians, possibly because of reduced muscle OCTN2 content. Thus, the greater whole-body carnitine retention observed after a single dose of l-carnitine in vegetarians was not attributable to increased muscle carnitine storage.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Biological Transport
  • Carnitine / blood
  • Carnitine / metabolism*
  • Carnitine / urine
  • Diet, Vegetarian*
  • Humans
  • Hyperinsulinism / metabolism*
  • Male
  • Muscle, Skeletal / metabolism*
  • Organic Cation Transport Proteins / genetics
  • Organic Cation Transport Proteins / metabolism*
  • RNA, Messenger / metabolism
  • Young Adult


  • Organic Cation Transport Proteins
  • RNA, Messenger
  • Carnitine