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A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 23
  1. M K Ranchordas1,
  2. E Blomstrand2,
  3. P C Calder3,
  4. L M Burke4,
  5. S J Stear5,
  6. L M Castell6
  1. 1Department of Sport, Faculty of Health and Wellbeing, Sheffield Hallam University, Sheffield, UK
  2. 2The Swedish School of Sport and Health Sciences, Stockholm, Sweden
  3. 3School of Medicine, University of Southampton, Southampton, UK
  4. 4Australian Institute of Sport, Canberra, Australia
  5. 5Performance Influencers Limited, London, UK
  6. 6University of Oxford, Oxford, UK
  1. Correspondence to L M Castell, University of Oxford, Green Templeton College, Oxford OX2 6HG, UK; lindy.castell{at}gtc.ox.ac.uk

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Introductory remarks

Little is known about the naturally occurring phospholipid, lecithin, in terms of its effects on athletes, apart from its link with choline. Although branched-chain amino acid (BCAA) supplementation was discussed in an earlier article in this series, it is appropriate to discuss leucine separately, since many athletes, both young and old, use it routinely these days. It is rare for individuals to be deficient in linoleic acid, since it is widely available in the diet, and consequently it does not appear to be taken often by athletes. In the late 1960s, γ-linolenic acid (GLA) supplementation was first given as a therapeutic agent using mixed triglycerides with/without GLA in claudicants undertaking leg exercise. The majority of studies on GLA since then have been clinical but there is some interest in GLA as a supplement in athletes.

Leucine

E Blomstrand

Leucine is one of the three BCAAs and is an essential amino acid (EAA) that has to be provided in the diet. Besides serving as building blocks for protein synthesis, leucine can also regulate the rate of protein synthesis via a stimulatory effect on enzymes involved in the translation of specific mRNAs.1 Direct stimulation by leucine of the rate of protein synthesis in muscle tissue was first demonstrated in various preparations from experimental animals and, more recently, in the intact animal after oral administration.2 Infusion of leucine in human subjects was shown to improve the net protein balance and to increase phosphorylation/activation of the regulatory enzyme 70-kD ribosomal protein S6 kinase (p70S6k), indicating a stimulatory effect of leucine on protein synthesis also on human muscle after oral ingestion, although this remains to be confirmed.3 4

When leucine is ingested together with the other EAAs after resistance exercise, the rate of protein synthesis increases …

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