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25-09-2011 | Article

Carbohydrate supplementation improves exercise endurance


Free abstract

MedWire News: Carbohydrate supplementation can have large performance benefits in endurance exercise, shows a meta-analysis of published studies.

However, the performance effect is dependent on the composition and administration regimen of the supplement, note Tom Vandenbogaerde and Will Hopkins, from Auckland University of Technology in New Zealand.

"A good supplementation regimen is to ingest carbohydrate before and during exercise in many boluses, with the first bolus up to 4 hours before the start of exercise," they say.

In addition, "supplements or foods containing high concentrations of carbohydrate or more than small amounts of fructose should be avoided."

After adjusting for publication bias,a total of 73 studies published between 1979 and 2009, in which carbohydrate supplements were consumed with or without protein before and/or during exercise, were included in the analysis.

Of note, publication bias was substantial, providing up to a 2% increase in the performance effect of supplements, which, the researchers say, "underscores the value of meta-analysis in providing more realistic performance effects of treatments."

Factors that the researchers considered as predictors of performance effects (assessed in time-to-exhaustion tests or time trials with or without a preload) were: total percentage of carbohydrate and protein; rates of ingestion of glucose, sucrose, fructose, and glucose polymers; and the inclusion of salt.

As reported in the journal Sports Medicine, the performance effects of carbohydrate supplements ranged from improvements of approximately 6% to impairments of approximately 2%.

The best supplement was a carbohydrate-plus-protein drink which provided approximately 0.7 g/kg per hour of glucose polymers, 0.2 g/kg per hour of fructose, and 0.2 g/kg per hour of protein.

"A possible explanation for this combination of carbohydrates is that the increase in carbohydrate oxidation rate with ingestion of several varieties of carbohydrate helps the athlete sustain exercise intensity," remark Vandenbogaerde and Hopkins.

Increases in the benefit of a supplement were small to moderate if the first "bolus" was ingested 1-4 hours before exercise compared with at the start of exercise. Furthermore, small benefits were seen when the frequency of ingestion was increased to three boluses per hour.

Supplements that provided more than 0.25 g/kg per hour of fructose, however, were associated with substantial reductions in performance, notes the team. Unexpectedly, effects were trivial when salt was included in the supplement.

The researchers stress that their meta-analysis did not account for individual responses. Therefore, "individual athletes may obtain no benefit or even impairment in performance with carbohydrate ingestion," they conclude.

By Nikki Withers