Effect of l-carnitine supplementation on the body carnitine pool, skeletal muscle energy metabolism and physical performance in male vegetarians
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More than 95 % of the body carnitine is located in skeletal muscle, where it is essential for energy metabolism. Vegetarians ingest less carnitine and carnitine precursors and have lower plasma carnitine concentrations than omnivores. Principle aims of the current study were to assess the plasma and skeletal muscle carnitine content and physical performance of male vegetarians and matched omnivores under basal conditions and after l-carnitine supplementation.
Sixteen vegetarians and eight omnivores participated in this interventional study with oral supplementation of 2 g l-carnitine for 12 weeks. Before carnitine supplementation, vegetarians had a 10 % lower plasma carnitine concentration, but maintained skeletal muscle carnitine stores compared to omnivores. Skeletal muscle phosphocreatine, ATP, glycogen and lactate contents were also not different from omnivores. Maximal oxygen uptake (VO2max) and workload (P max) per bodyweight (bicycle spiroergometry) were not significantly different between vegetarians and omnivores. Sub-maximal exercise (75 % VO2max for 1 h) revealed no significant differences between vegetarians and omnivores (respiratory exchange ratio, blood lactate and muscle metabolites). Supplementation with l-carnitine significantly increased the total plasma carnitine concentration (24 % in omnivores, 31 % in vegetarians) and the muscle carnitine content in vegetarians (13 %). Despite this increase, P max and VO2max as well as muscle phosphocreatine, lactate and glycogen were not significantly affected by carnitine administration.
Vegetarians have lower plasma carnitine concentrations, but maintained muscle carnitine stores compared to omnivores. Oral l-carnitine supplementation normalizes the plasma carnitine stores and slightly increases the skeletal muscle carnitine content in vegetarians, but without affecting muscle function and energy metabolism.
KeywordsVegetarians l-carnitine supplementation Spiroergometry Skeletal muscle Energy metabolism
We would like to thank Beatrice Vetter, Liliane Todesco and Réjane Morand for performing biochemical analyses. We also express our appreciation to the Lonza Group, Basel, Switzerland, especially toward Miss Ulla Freitas for critically reading the manuscript and for supporting this research financially. The study was financially supported by a Grant from the Swiss National Science Foundation (31003A_132992/1) to SK. Lonza provided the carnitine tartrate capsules and part of the salary of one of the co-authors (P. Roberts). Lonza had no impact on the protocol, but received a prefinal version of the manuscript and could give comments before publication.
Conflict of interest
None of the authors reports any conflict of interest regarding this manuscript.
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