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A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 26
  1. N A Burd1,
  2. A Jeukendrup2,
  3. M B Reid3,
  4. L M Burke4,
  5. S J Stear5,
  6. L M Castell6
  1. 1Department of Human Movement Sciences, Maastricht University Medical Centre, Maastricht, The Netherlands
  2. 2University of Birmingham, Birmingham, UK
  3. 3Department of Physiology, University of Kentucky, Lexington, Kentucky, USA
  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

Part 26 provides an overview of three supplements with different characteristics of potential contribution to exercise performance and different levels of scientific support for this potential. Methionine is an amino acid with an important role, in addition to its contribution to protein metabolism, namely, as a precursor of creatine. N-acetylcysteine has an important role in glutathione resynthesis and therefore contributes to antioxidant status. Finally, we discuss a new approach to providing carbohydrates in sports supplements – known as multiple transportable carbohydrates (MTC) – which overcomes the usual intestinal absorption limits to allow higher rates of carbohydrate consumed during exercise to be available as a muscle fuel.

Methionine

N A Burd

Methionine is an indispensible amino acid that acts as a substrate, much like the other indispensible amino acids, for building functional muscle proteins. It is clear, however, that methionine also holds a unique role, when compared against the other indispensible amino acids, as it serves as a methyl group donor for DNA/RNA intermediates and for the synthesis of cysteine.1 Daily methionine requirement, reported as a constituent of the requirement for total sulphur amino acids, is 13–15 mg/kg-1/day-1 with the risk for toxicity manifesting only at levels exceeding >10-fold excess in humans.2 3 Daily requirements of methionine are easily obtained in the diet due to its widespread abundance in meats, eggs, cheeses, fruits and vegetables. However, vegan athletes may need increased self-awareness of daily methionine intake.4

What purpose does supplemental methionine have in an athlete's diet for enhancing performance/recovery? Very little, provided the athlete is healthy and consuming a …

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