Vegetarians have a reduced skeletal muscle carnitine transport capacity1234
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 vegetaria...
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Published in | The American journal of clinical nutrition Vol. 94; no. 3; pp. 938 - 944 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Inc
01.09.2011
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Subjects | |
Online Access | Get full text |
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Summary: | 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. |
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ISSN: | 0002-9165 1938-3207 |
DOI: | 10.3945/ajcn.111.012047 |