Journal Title (Medline/Pubmed accepted abbreviation): Sports Med.
Page numbers: 449-461
Summary of the review article:
It has been established that ingestion of fluid during exercise maintains blood volume and prevents overheating. Carbohydrates in sports beverages have an added effect on sports performance however, interestingly, only a small amount of glucose reaches circulation during the exercise bout and therefore only marginally affects blood glucose concentrations, carbohydrate oxidation, and glycogen sparing. Also, intravenous infusion of carbohydrate has a smaller effect on performance than ingestion. This leads people to believe that the presence of carbohydrate in the digestive system alone (ex. mouth) could affect metabolism and potentially enhance sports performance. This review summarizes studies that have investigated the “central” or “non-metabolic” effects of a carbohydrate mouth rinse on sports performance.
Only 6 studies have been completed to date investigating the effects of a carbohydrate mouth rinse, 4 with cyclists and 2 with runners. Four independent studies involved cyclists completing an approximately 60 min long time trial. In 3 of the 4 studies a majority of the cyclists had a better time with a carbohydrate mouth rinse even when the placebo was an artificially sweetened beverage that was identical in taste to the carbohydrate beverage. A carbohydrate mouth rinse vs. a calorie-free mouth rinse aided in the performance of runners in one study but not the other.
Athletes who performed better with the carbohydrate rinse did not perceive higher exertion. Also, runners chose faster speeds subconsciously on the treadmill than they did with the placebo.
It is thought that there are receptors in the mouth that can distinguish between compounds that are nutritive carbohydrates and compounds that are not (such as artificial sweeteners). Activation of these receptors stimulates “reward centers” in the brain that could increase the mood/motivation of the athlete and increase performance through a psychological means.
Key practice applications:
In the few studies that have investigated the carbohydrate mouth rinse, this technique appears to be effective compared to rinsing the mouth with water or a non-nutritive solution. Spitting out the beverage, however, is likely not more beneficial than actually ingesting the beverage if the solution resides in the oral cavity for the same amount of time. Those who may be interested in the carbohydrate mouth rinse would be athletes who experience gastrointestinal discomfort from ingesting sports beverages during exercise or those who want to avoid consuming the calories. Event intensity and duration are also likely key influencers regarding whether or not carbohydrate mouth-rinsing is preferred to actual ingestion of the carbohydrate. During more intense or longer duration exercise, the physiological effects of carbohydrate ingestion become more important.