Science of Sport: Carbohydrate mouthwash is ergogenic

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Supplementary carbohydrate does not have to be swallowed or infused in order to exert an ergogenic effect. A remarkable new UK study has found that a carbohydrate mouthwash, rinsed around the mouth at regular intervals during a one-hour cycling time trial, led to a significant improvement in power output and performance time.

Carbohydrate (CHO) ingestion immediately before and during exercise of a relatively short and intense nature has been shown to boost performance in previous research, with no obvious metabolic explanation for this effect.

The team responsible for the current study got the idea of studying carbs in mouthwash form from their own observation that a glucose infusion (as opposed to oral administration) had no beneficial effect on performance in a simulated 40k time trial. ‘These results suggest,’ they explain, ‘that oral CHO may exert its effects during high-intensity exercise through a central action, improving motor drive or motivation, mediated by receptors in the mouth or GI tract.’

The aim of the study was to investigate the possible role of carbohydrate receptors in the mouth in influencing exercise performance. The use of a mouth rinse treatment, which was spat out without being swallowed, removed any influence of the gut and CHO oxidation on performance.

Seven male and two female endurance cyclists completed two performance trials, in which they had to accomplish a set amount of work as quickly as possible. On one occasion, a 6.4% maltodextrin solution (CHO) was rinsed around the mouth for every 12.5% of the trial completed, and on the other a placebo liquid (water) was used in the same way.

The results were quite clear:

• Performance time was significantly faster in the CHO trial compared with placebo – an average of 59.57 minutes compared with 61.37 minutes, representing a 2.9% improvement;
• Power output with CHO was correspondingly higher, at 259W compared with 252W for placebo;
• There were no differences in heart rate or rating of perceived exertion between the two trials.

‘To our knowledge,’ say the researchers, ‘this is the first study that has investigated the role of the mouth as a factor in CHO supplementation during high-intensity exercise performance.’

How can the effects be explained? The fact that the solution was spat out and not swallowed makes it unlikely that the performance improvements were related to metabolic action of the CHO, as minimal quantities of the maltodextrin would have entered the gut.

The researchers speculate that triggering of receptors within the oral cavity by the CHO could have resulted in the stimulation of the reward and/or pleasure centres in the brain, leading to enhanced motivation. Such responses are known with other substances, such as chocolate.

Meanwhile, they conclude that ‘the existence of such CHO receptors in the mouth and their effect on performance warrants further investigation. These additional studies should involve a variety of rinse formulations and should rule out the possibility of potential placebo effects.’

Med Sci Sports Exerc, vol 36, no 12, 2107- 2111, 2004

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