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A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance–Part 20
  1. K Currell1,
  2. W Derave2,
  3. I Everaert2,
  4. L McNaughton3,
  5. G Slater4,
  6. L M Burke5,
  7. S J Stear6,
  8. L M Castell7
  1. 1English Institute of Sport, Bisham Abbey Performance Centre, Marlow, Buckinghamshire, UK
  2. 2Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium
  3. 3Faculty of Health Sciences and Medicine, Bond University, Queensland, Australia
  4. 4Faculty of Science, Health and Education, University of the Sunshine Coast, Maroochydore, Queensland, Australia
  5. 5Department of Sports Nutrition, Australian Institute of Sport, Belconnen, Canberra, Australia
  6. 6Performance Influencers Limited, London, UK
  7. 7University of Oxford, Green Templeton College, Oxford, UK
  1. Corresponding to L M Castell, University of Oxford, Green Templeton College, Woodstock Road, Oxford OX2 6HG, UK; lindy.castell{at}gtc.ox.ac.uk

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Introductory remarks

As usual, the alphabet throws together a mixture of supplements with different levels of popularity and scientific support. Part 20 covers some rarely reported, studied and/or little used supplements in sport: glycine, histidine and inosine. The majority of human studies of supplementation with the essential amino acid histidine has involved clinical work. In terms of athletic performance, there is current interest in supplementation strategies to increase muscle content of the histidine-containing dipeptide (HCD), carnosine. Despite some interest in the use of a chicken breast extract (CBEX) described in this article, most of the focus in this area involves β-alanine supplementation (covered in part 5). There was some interest in inosine as an ergogenic aid in the 1990s but it appears not to have been studied since then. Meanwhile, there appears little role for glycine supplementation in sport although some interest in glycine-containing compounds is possible. β-Hydroxymethyl β-butyrate (HMB) is much more well known, with marketing usually targeting bodybuilders.

Glycine

K Currell

Glycine is the smallest amino acid; it is non-essential and can be synthesised from serine. Glycine is present in most proteins and is particularly highly concentrated in collagen. Consequently, one of the highest food sources of glycine is gelatin. Glycine is also one of the three amino acid components of glutathione, which is a key component of the body's defences against oxidative stress; however, it is thought that glycine availability is not the limiting step in glutathione synthesis. Glycine ingestion increases plasma concentrations of insulin in a similar way to other amino acids.1 Glycine is also an inhibitory neurotransmitter.

There is little research on supplementation with glycine. Research has looked at its potential role in decreasing inflammation.2 Sport specific research has focused on combining glycine with other nutrients. Glycine-propionyl-L-carnitine (GPLC) has been shown to influence exercise performance,3 decrease oxidative …

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