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A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance—Part 19
  1. L M Burke1,
  2. S J Stear2,
  3. A Lobb3,
  4. M Ellison4,
  5. L M Castell5
  1. 1Australian Institute of Sport, Canberra, Australia
  2. 2Performance Influencers Limited, London, UK
  3. 3Health Care Delivery Science Program, Dartmouth College, Hanover, New Hampshire, USA
  4. 4English Institute of Sport, Sheffield, UK
  5. 5University of Oxford, Green Templeton College, 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

Glycerol, guarana and the weight-loss agent, hydroxycut, occupy part 19; glycine will appear in part 20. The ubiquitous product, glycerol, is used both orally, for example, as an emulsifier in ice cream and topically, for example, as glycerine in hand cream. In the area of sports nutrition, glycerol plays a role in improving hydration status, as described in detail below. Guarana has been used for centuries as a stimulant in South America, due to its high caffeine content; it also contains xanthine alkaloids, such as theobromine and theophylline, which enhance the effects of caffeine. Further information on caffeine and sports performance can be found in part 6 of this series.1 Unlike glycerol and guarana, hydroxycut is an example of a multi-ingredient supplement with a proprietary formulation that presents special challenges when assessing safety and efficacy, including uncertainty as to which ‘active’ ingredients may provide the desired effects and frequent formulation changes.

Glycerol

L M Burke

Glycerol is a 3-carbon sugar alcohol that provides the backbone of triglycerides and is naturally found in foods as a component of dietary fats. However, its various physical and chemical properties are valuable in food technology: glycerol is added to manufactured foods and drinks as an emulsifier, humectant, sweetener, filler and thickener. Its viscosity also makes it useful as a component of lotions and creams, explaining its common availability for purchase in purified form under the name of glycerine. Although it has been suggested as a gluconeogenic precursor that could provide a substrate for exercise, the ingestion of glycerol by athletes is best known for its role as an osmolyte. When ingested or released following lipolysis, glycerol contributes to the osmotic pressure of body fluids until it is slowly metabolised. When consumed simultaneously with a substantial volume of fluid, there is a temporary retention of this fluid and …

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