Can mouthwash make you faster?
No, we aren’t talking about Listerine, Scope, or any of those other mouthwashes that are intended to give you a clean mouth, fresh breath, and make you more kissable. We are talking about the opposite of that: a sweet drink that makes your mouth sticky with sugar, and you don’t even have to drink it. How does that work? First, let’s start with a little background.
Most athletes understand that moderate to high intensity exercise is fueled primarily by carbohydrate. We have large stores of fat, but the energy from that fat cannot be released quickly enough to fuel your muscles at those higher intensities. The chemical energy in carbohydrates can be turned into mechanical energy at a much faster rate. So pedaling harder or putting one foot in front of the other with any reasonable intensity requires carbohydrates as fuel. The problem with carbohydrate is that you can only store so much of it. Once that carbohydrate done, you’ll slow to a pace that can be sustained using only fat for energy. You’ll be slow, and you probably won’t be very happy. In the 90s, researchers firmly established that supplementing with carbohydrates, usually in the form of sugary drink, improved performance. But here’s the thing: Carbohydrate supplementation improved high intensity performance even when the intensity and duration of the exercise was not enough to deplete the athlete’s stores of carbohydrate. And these improvements were real, meaningful improvements, ranging from as little as little as 2.3-11%. What does this mean in real world terms? It means that improvements in a 40K cycling time trial, or a half marathon are measured not in seconds, but minutes. So what is going on here?
A large breakthrough came in 2004, when Doctor Carter from the University of Birrmingham did something new and interesting. He bypassed the mouth. Carter and colleagues had cyclists do a 40K time trial while receiving and infusion of either saline, or a carbohydrate solution at a rate of 1g/min of carbohydrate (similar to what an athlete could drink and absorb the good old fashioned way). As you might expect, blood glucose level in the carbohydrate group went up. What might surprise you is that there was no improvement in performance. That athletes didn’t go any faster. Carter’s follow up was to have athletes do another 40K time trial. But this time they would take a mouthful of carbohydrate drink, swirl it around for 5 seconds and then spit it out. You can probably guess what happened: The athletes improved on the order of about 3%, similar to if they had actually swallowed the drink. Once again, the improvement could be measured not just in seconds, but in minutes. Several other researchers have found similar results, but not all of them have. But there does seem to be a growing body of evidence that at least in some circumstances, a carbohydrate rinse improves endurance performance. So how does it work?
“Central governor theory” suggests that one of the limiters of performance is the brain, and I’m not talking about mental toughness here. According to central governor theory, the brain is constantly taking in all sorts of information about the physiological state of the body, and then regulating muscle recruitment based on that information. The evolutionary value of this would be to reduce the likelihood of self-harm. The brain tells the body to “ease up” to keep from hurting itself. The research on carbohydrate mouthwash/rinses suggests that some sort of chemoreceptors in the mouth tell the brain “more carbohydrate is coming!” so the brain allows the muscles to keep on pumping away.
Of course not everyone agrees. A few studies have shown no effect with the carbohydrate rinse. A few of these studies may have found an effect if the sample size were larger (the larger the sample, the easier it is to find differences). Studies that included 4 hours or more of fasting before the exercise session were more likely to find a benefit. So starting with full stores of muscle and liver glycogen may blunt the effect of the rinse. It also appears that the rinse doesn’t help with efforts of about 30 minutes or less, and nobody has really looked at efforts over 70 minutes.
So how can you put this information to use in a practical way? To some extent, this research has value even if we can’t put it directly to use right now, as it gives us insight into what limits human performance. But I think we can put it to practical use. In most cases, athletes should simply swallow their carbohydrate mix rather than spit it out. But athletes that experience an upset stomach ( GI distress) may be able to get the performance benefits of carbohydrate supplementation, while avoiding the distress. Some experimentation during training may be required, and the athlete may find it best to “rinse and spit”, “spit one, swallow one”, or something along those lines. The other practical implication is for people that are training for weight loss. It would be theoretically possible to use the “rinse and spit” method to complete a more intense workout, while also minimizing calorie intake.
So next time your legs are heavy and your stomach is in knots, just try the rinse and spit.
Questions? What would you like to see me write about next? Email me: firstname.lastname@example.org
Resources and further reading
Beelen, M., J. Berghuis, B. Bonaparte, S.B. Ballak, A.E. Jeukendrup, and L.J. van Loon (2009). Carbohydrate mouth rinsing in the fed state: Lack of enhancement of time-trial performance. Int. J. Sport Nutr. Exerc. Metab. 19:400-409.
Carter, J.M., A.E. Jeukendrup, C.H. Mann, and D.A. Jones (2004). The effect of glucose infusion on glucose kinetics during a 1-h time trial. Med. Sci. Sports Exerc. 36:1543-1550.
Carter, J.M., A.E. Jeukendrup, and D.A. Jones (2004). The effect of carbohydrate mouth rinse on 1-h cycle time trial performance. Med. Sci. Sports Exerc. 36:2107-2111.
Chambers, E.S., M.W. Bridge, and D.A. Jones (2009). Carbohydrate sensing in the human mouth: Effects on exercise performance and brain activity. J. Physiol. 587:1779-1794. Fares, E.J., and B. Kayser (2011). Carbohydrate mouth rinse effects on exercise capacity in pre- and postprandial states. J. Nutr. Metab.2011:385962.
Jeukendrup, A.E., S. Hopkins, L.F. Aragon-Vargas, and C. Hulston (2008). No effect of carbohydrate feeding on 16 km cycling time trial performance. Eur. J. Appl. Physiol. 104:831-837.
Luden ND, Saunders MJ, D’Lugos AC, et al. Carbohydrate Mouth Rinsing Enhances High Intensity Time Trial Performance Following Prolonged Cycling. Nutrients. 2016;8(9):576. doi:10.3390/nu8090576.
Noakes, T.D. (2000). Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance. Scand. J. Med. Sci. Sports 10:123-145.
Silva T de A e, de Souza MEDCA, de Amorim JF, Stathis CG, Leandro CG, Lima-Silva AE. Can Carbohydrate Mouth Rinse Improve Performance during Exercise? A Systematic Review. Nutrients. 2014;6(1):1-10.