Nutrition and Metabolism in Sports, Exercise and Health by Jie Kang

Author:Jie Kang [Kang, Jie]
Language: eng
Format: epub, pdf
Tags: Science, Medical, Life Sciences, Health & Fitness, Biochemistry, Human Anatomy & Physiology, Nutrition, Sports Medicine
ISBN: 9780415578783
Publisher: Routledge
Published: 2012-04-05T06:46:01+00:00

Inosine

Inosine is a nucleoside, a purine base comparable to adenine, which is one of the structural components of ATP. It is found naturally in brewer’s yeast and organ meats. Inosine is not considered an essential nutrient. The body synthesizes inosine from precursor amino acids and glucose. Inosine, in the form of nucleotide inosine monohydrate (IMP), is used to make adenine monophosphate (AMP), which in turn can be phosphorylated to the high-energy phosphate compound ATP. Strength and power athletes supplement with inosine in the belief that it increases ATP stores, thereby improving training quality and competitive performance. Inosine is also thought to improve endurance performance. It has also been theorized that inosine participates in the formation of 2,3-diphosphoglycerate (2,3-DPG), a substance in red blood cells that facilitates the release of oxygen from hemoglobin to the tissue. Other claims regarding inosine include its role in: (1) stimulating insulin release to enhance glucose delivery; (2) augmenting cardiac contractility; and (3) acting as a vasodilating agent. It is mainly because of these theoretical considerations that inosine has been extolled as an ergogenic supplement to improve both anaerobic and aerobic performance.

Objective data do not support the ergogenic role of inosine supplementation in improving either aerobic or anaerobic performance. In fact, it has been suggested that this supplement may have ergolytic effects under some conditions. In one carefully conducted study, trained men and women were administered 6 g per day of inosine or placebo for two days, but no change was observed in three-mile treadmill run time, VO2max, or perceived exertion (Williams et al. 1990). After a 30-min break, subjects performed another run in which speed was kept constant but the treadmill grade increased gradually. It was found that time to exhaustion in this run was actually longer during the placebo trial, suggesting a possible negative effect of inosine supplementation. In another study, male competitive cyclists received either a placebo or 5 g per day of oral inosine supplement for five days (Starling et al. 1996). They then performed a Wingate cycle test, a 30-min self-paced bicycle endurance test, and a constant load, supramaximal cycling sprint to fatigue. No significant differences occurred in any of the criterion variables in terms of performance or blood 2,3-DPG concentrations between placebo and treatment conditions. Similarly, this study also showed that cyclists fatigue nearly 10% faster on the supramaximal sprint test when they consumed inosine than without it, again indicating that inosine can be detrimental to performance.

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