Yes, you read that right! Repeated research has shown that by simply rinsing your mouth with a carbohydrate solution for five seconds, you can shave off up to one minute off of a 40km time trial and increase total distance run over both a 30- and 60-minute run.
Asker Jeukendrup studied cyclists performing a 40km time trial. Subjects were asked to rinse their mouths with a non-sweet, tasteless maltodextrin solution containing carbohydrate for five seconds and not swallow it while performing the 40km TT. The rinsing protocol was standardized, and subjects rinsed and spit into a bowl after five seconds. The results were incredible. Performance was improved with the carbohydrate mouth rinse vs. the placebo, and the results were as effective as similar studies in which cyclists ingested the carbohydrates. The 40km TT was completed one minute faster without any of the carbohydrate actually entering the body (carbohydrates cannot be absorbed in the mouth). So what’s going on?
To date the theory is that perhaps there are receptors in the mouth that send signals to the brain that food is on the way. Just this signal alone could change the body’s perceived effort, making the exercise easier for that time.
Follow-up studies were done to take a look at brain activity using a scan called fMRI, and researchers looked to see if brain activity differed when subjects rinsed with a placebo instead of a carbohydrate mouth rinse. They found that the carbohydrate solution activated areas of the brain related to reward centers and motor control.
During hard exercise the brain receives many signals, and over time these signals can begin to be perceived by the brain as unpleasant. Typically this leads to inhibition of motor output, often referred to as central fatigue. It seems plausible that signals from the carbohydrate receptors in the mouth would counteract some of these negative signals. Exactly how this occurs is unknown, but it’s possible that this signal to the brain gives the message that you can relax a bit because energy is on the way. There is clearly communication between the mouth and the brain even before carbohydrates enter the body. This could give good reason to just suck on candies for the same effect, but that has not yet been studied.
Researchers have also investigated whether the mouth-brain relationship is related to sweetness. They used an artificial sweetener in the same mouth-rinsing protocol and found that the same areas of the mouth were not stimulated as they were with the tasteless, non-sweet maltodextrin. This would again indicate that there are carbohydrate receptors in the mouth and that they are separate from sweetness receptors, some of which are able to identify authentic sugar from artificial. To date there are no known carbohydrate receptors in the human mouth, so this definitely will demand more research into this area.
In practice it appears that simply rinsing your mouth during exercise lasting 30-60 minutes can have significant performance outcomes. As we already know, it isn’t necessary to eat calories during exercise of such short duration if you are properly fueled prior to it. However, this new data suggests that it’s worth rinsing your mouth with a carbohydrate solution. Ingesting the carbohydrate solution drink had the same outcome, so there’s no disadvantage to drinking the drink during exercise, besides the calories ingested. Time will tell about eating candies instead of mouth rinsing!