Energy Boost From Carbohydrate Rinse May Be Dose-Dependent

Laird Harrison

June 16, 2015

SAN DIEGO — A carbohydrate solution used as a mouth rinse can give athletes a performance boost that increases with dose, a new meta-analysis suggests.

"A greater dose of carbohydrate has a greater effect size," said Scott Conger, PhD, from Boise State University in Idaho.

Over the past 10 years, a series of studies has shown that athletes who rinse their mouths with a solution containing carbohydrates perform better than athletes rinsing with water alone or with water and artificial sweetener.

The research suggests that carbohydrates in the mouth trigger the central nervous system to release glycogen. However, the effect is only temporary, Dr Conger told Medscape Medical News. "After an hour, glycogen depletion is going to be a factor."

Although most studies show that the technique works, others have shown no effect or even a negative one. To reconcile these disparate outcomes, Dr Conger and his colleagues examined 180 studies exploring athletic performance associated with carbohydrate mouth rinse.

Dr Conger presented findings from the meta-analysis here at the American College of Sports Medicine 62nd Annual Meeting.

After narrowing down their search results, the team evaluated 16 studies that were published in peer-reviewed journals, used human subjects, involved an endurance bout of at least 10 minutes, measured exercise performance, and compared the carbohydrate rinse with either water or a placebo rinse.

They used statistical means to account for potential biases in studies that had small sample sizes. In studies that had more than one outcome, they averaged the outcomes.

In the calculation of overall effect size, a negative number indicated the control was more effective than the carbohydrate, a value of zero indicated that there was no difference between the two, and a positive number indicated that the carbohydrate rinse was more effective than the control.

In this model, an effect size of 0.2 was considered small, an effect size of 0.5 was considered moderate, and an effect size of 0.8 was considered large. There was no maximum effect size.

In the 16 studies, effect size ranged from –0.517 to 1.009. In the meta-analysis, the overall effect size was 0.28, which was significant (P =.001).

Dr Conger and his colleagues conducted an analysis to assess the influence of different variables.

The effect size was slightly larger in studies that used a placebo, such as an artificial sweetener, as the control than in studies that used water (0.295 vs 0.247; P = .8). The effect size was also larger when participants rode bicycles than when they ran (0.311 vs 0.211; P = .61), and when participants ate before their trial than when they fasted (0.376 vs 0.297; P = .66).

The effect size was smaller when glucose or maltodextrin was used than when multiple carbohydrates were combined (0.272 vs 0.311; P = .87).

The effect size was significantly larger when a 10% to 12% carbohydrate solution was used than when a 6% to 7% solution was used (0.768 vs 0.222; P = .01).

The majority of research on carbohydrate mouth rinses shows some effect, said Nancy Clark, MS, RD, who is a sports nutrition dietitian in Boston.

"Sometimes people don't want to have anything in their stomachs before they do a really hard workout," she told Medscape Medical News. "There is really no downside."

Dr Clark and Dr Conger have disclosed no relevant financial relationships.

American College of Sports Medicine (ACSM) 62nd Annual Meeting: Abstract 1300. Presented May 28, 2015.

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