Taking on carbohydrates during exercise is a well-described way to help fuel muscle and endurance. But the research in this area took a decidedly strange turn some years ago when it was shown that the simple act of just swishing a carbohydrate-containing drink in your mouth for a few seconds can also have a performance advantage. This was research that I simply could not believe when I first came across it, but it has been replicated many times now. In this podcast, I’ll look at just how carbohydrate mouth rinsing can improve sports performance.
The time was 2004 and it marked the emergence of the first publication of dedicated research into the effect of carbohydrate mouth rinsing on sports performance. The research, born out of the observation that glucose infusions directly into the blood did not seem to offer a performance enhancement in 1-hour cycling time trials the same as when carbohydrate drinks were taken on, the super novel question being asked was if somehow the mouth sensing of carbohydrate could be playing a role. Testing this in endurance cyclists, there was a clear performance benefit of periodic mouth rinsing for 5 seconds at a time with a 6.4% carbohydrate drink (which was spat out rather than swallowed) versus a placebo drink.
If the research had of stopped there, it would have been seen as a novel oddity. But it didn’t with more and more research, that now counts over a dozen studies, confirming the finding with most studies showing a benefit. And the benefit is seen in both cycling and running studies done in laboratory conditions.
If you want a nice summary of this research and a great graph showing the performance benefit in each study, then head over to the website of one of the key researchers in this area Asker Jeukendrup which I’ll link to in the show notes. https://www.mysportscience.com/post/2015/05/20/spit-or-swallow-carb-mouth-rinse-and-performance
For the studies that did not find a benefit, it was more a case of them not getting to a level of statistical significance so this could be related to not having enough people in them. Also, studies that did show a benefit were more likely to run for longer as studies under 30 minutes do not show a benefit. And some studies that showed a benefit were more likely to have a longer period of fasting before the study as this may help prime the carbohydrate sensing benefit.
And the benefit works for either glucose-based carbohydrate drinks like your classic sports drinks or a carbohydrate source called maltodextrin that is essentially colourless and tasteless and serves as a good experimental drink to use to compare it to water placebo. So, this shows it isn’t taste sensations related to sugar driving a benefit, but rather a direct effect of carbohydrates on receptors in the mouth via specialised receptors independent of sweetness.
As for that mechanism, it is still not fully understood, but clearly is related to a mouth sensing benefit acting on the brain and central nervous system which is enough to stimulate reward centres in the brain to make the athlete feel better, reduce the perception of effort and enhance pacing strategies.
This mouth-sensing performance-enhancing effect of carbohydrates comes into play in shorter high-intensity events of 45 to 75 minutes in duration and this is where most of the research has been done. If you’re training and competing well past that time, then taking on carbohydrates to replenish losses would be the main priority.
The most common protocol for mouth rinsing is around 5 to 10 seconds at regular intervals and then spitting it out afterwards. A word of warning: please be considerate of your fellow humans around you in your training and competing when doing this!
And just to add an extra layer of crazy to this whole field, there is now some research to show that perhaps even the colour of the carbohydrate-containing drink could also have a performance-enhancing effect. You see, some of the research so far on the effects of carbohydrates have used as its placebo drink one that has been artificially sweetened to allow a comparison made to sugar-based sports drinks. But what sort of placebo-effect could a placebo drink be having?
In a small trial, 10 active people underwent two treadmill runs at self-selected speeds. During the run, they mouth rinsed several times both during the 12-minute warm-up and 30-minute run for 5 seconds each with either a clear or pink-coloured artificially sweetened solution. The critical point is that both solutions were sweetened to the same level with sucralose so it was colour that was the only difference between the drinks. A week later, each person did another treadmill session using the alternative sports drink to what they had in the first trial.
So, what happened? When compared to the clear solution, the total distance covered, and average speed increased by over 4 percent when a mouth rinse was performed with the pink solution. Similarly, feelings of enjoyment also increased when rinsing with the pink solution compared to the clear solution. And I’ll link to this study in the show notes. https://pubmed.ncbi.nlm.nih.gov/34055861
The results here are a clear example of the placebo effect as the only difference between the drinks was colour. Perhaps it is an example where people have been conditioned that sports drinks, which are linked with sports performance, are usually bright colours so the pink here is a marker for that so that is enough to have real effects on the brain on perceived exertion. Colour is an important guide to properties we attach to food with a previous study finding that white is associated with saltiness; green, black, and violet with bitterness; and red, orange, and pink with sweetness. The sports drinks manufacturers are all over this research.
None of this means that carbohydrate-mouth rinsing studies don’t have validity in their own right – they certainly do as keep in mind the placebos in some of those studies were artificially sweetened drinks.
So, if you are going to use carbohydrate-containing drinks during sport, go for the bright coloured ones – red ones are the best as everyone knows that red makes you go faster.
So, let’s wrap this up with the practical implications of all this. For high-intensity endurance training and events lasting between 30 and 75 minutes, routinely rinsing a carbohydrate-containing drink around in the mouth for between 5 and 10 seconds has been shown to improve performance. This could present an advantage for athletes who are prone to GI problems from consuming carbohydrates, especially in these sorts of timeframes where it is very unlikely that depletion of carbohydrate stores would be an issue so there is less of a need to actually ingest them.
Once you get past 2 hours for an event, it is very unlikely that mouth rinsing carbohydrates will continue to have a beneficial effect and here the advice is to revert to more traditional fuelling and hydration strategies and drink your sports drink.
But it isn’t all pluses here as there could be a downside to mouth rinsing during high-intensity exercise because of disruptions to breathing and concentration. So, there is the research, and then there is how you action it in implementing it for the practicalities in your training. It is just as important to train your sports nutrition as you do your body and this is done well before race day.
So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.
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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.