Carbohydrate mouthwash boosts performance

Carbohydrates during exercise boost performance, that’s a given. But what do you do when your gut says no more and another sports drink seems like a bad idea? In this article, we're talking about carbohydrate mouth rinsing as an alternative when intake doesn't work. But can we really enhance our performance just by rinsing our mouth without swallowing? Research actually shows that the brain responds to energy-rich signals in the oral cavity, and this can reduce perceived effort and improve performance, especially at medium to high intensity. The mouth rinse doesn't replace energy intake in the long term, but it can be a smart emergency solution when your gut acts up.

There's no doubt that carbohydrate intake during activity is strongly linked to improved athletic performance, and we've written numerous articles on this subject before with plenty of references: 1, 2, 3.

But sometimes the stomach acts up due to stress, poor nutrition planning, or excessive intake of easily digestible carbohydrates during activity, often a combination of several factors. In such situations, the risks of adding more sports drink, gel, or carbohydrate-rich bars may outweigh the benefits. In those scenarios, a mouth rinse can be a potential lifesaver.

In a systematic review published in 2013, 11 studies were included where researchers controlled and investigated performance on a treadmill or exercise bike for about an hour with and without mouth rinse with sports drink.

• 9 of the 11 studies showed a significant performance increase in those who rinsed their mouth with a sports drink compared to a placebo (e.g., low-energy drink with sweetener).
• 8 of the articles were double-blind (neither participants nor researchers knew who received what).
• 3 studies were single-blind (participants were blind, but researchers knew the drink's content).

The intensity in the tests was medium to high (approximately 65% of maximal oxygen uptake – VO2max – or 75% of maximal power – Wmax) and the performance increase varied between 1.5% and 11.5% in the different studies. This roughly corresponds to an increase in average wattage of about 5-9 W during the trial period of approximately an hour.

There were small variations in how the mouth rinse was performed: all participants rinsed their mouth for 5-10 seconds, but the number of rinses varied between about 4-12 times per hour. In the majority of studies (7/11), participants experienced a taste difference between the drinks, but only two people in total could confidently guess which drink contained carbohydrates.

Three studies reported no performance increase with mouth rinse; in two of these, the participants were runners. Whether the effect is greater during cycling than running is possible, but it is too early to draw conclusions.

A study investigating the brain areas activated by the CHO mouth rinse (glucose and maltodextrin) identified significant activation in brain regions associated with reward, such as the insula/frontal operculum, orbitofrontal cortex, and striatum.

The effect appears to be lower or even non-existent when tests are performed just two hours after a meal, meaning when you have plenty of glycogen in your muscles and liver. The beneficial effect is likely not due to the rinsing action itself, but rather because energy-rich molecules in the mouth activate reward receptors. Participants rinsing with only water showed no effect in the studies tested here.

We can't definitively say that mouthwash helps late in a long race – you can't trick the body forever. At the same time, some studies show a greater effect when participants fasted longer. Whether the receptors in the oral cavity become more sensitive during fasting or why the effect becomes greater, we don't know, but it suggests that you might still benefit from mouthwash a few hours into a race.

Long story short: if you have a troublesome gut, mouthwash might be better than nothing at all. You can also rinse a gel in your mouth, which can be a smart and gentle compromise, especially if your gut starts acting up while running. 

If you have a sweet tooth and the craving steals your focus, you can try rinsing your mouth with a sweet, energy-rich drink and spitting it out. This way, your brain gets its reward without unnecessary calories – practical and a little cheeky in a good way 🙂

Now, a bit of biomedical nerdiness to explain why the brain/body loves our dear carbohydrates. 

We mainly have two fuels: fatty acids and glucose (protein is excluded in this comparison). Both require energy to break down (the energy investment phase) but ultimately provide energy in the form of adenosine triphosphate (ATP) (the energy generation phase). Both substances are composed of carbon units; ultimately, it is the carbon bonds we break for energy.

If we count the same number of carbon units (18 carbons), we get the following comparison:

• Fatty acid (stearic acid, 18 carbon units) provides 120 ATP and requires 26 oxygen molecules. Ratio: 120/26 = 4.62 ATP per O2.
• Glucose (3 × glucose molecules at 6 carbons = 18 carbon units) provides 96 ATP and requires 18 oxygen molecules. Ratio: 96/18 = 5.33 ATP per O2.

If we compare the same oxygen cost (exactly 26 oxygen molecules), glucose would provide 96 × (26/18) ≈ 139 ATP, while fatty acid provides 120 ATP. This means that glucose provides about 13% more ATP per given oxygen investment than fat according to these theoretical figures.

Another way to look at it is that you get 4.62 ATP per oxygen molecule when you oxidize fat and 5.33 ATP per oxygen molecule when you oxidize the same amount of carbon units as glucose. The result is that each energy unit from fat theoretically costs about 13.3% more oxygen to extract compared to glucose. In practice, when more parameters are involved, the difference becomes smaller and has in some trials proved to be about 7.2% instead of 13.3% (source).

This biochemical basis is part of the explanation why carbohydrates are often preferred for high-intensity work—they provide more energy per oxygen molecule and can therefore be more oxygen-efficient when the intensity is high.

Do you want a quick “cheat sheet” for when mouth rinse might be worth trying in practice? Let me know and I'll whip up a small checklist with concrete situations, frequency, and drink tips.

Listen to podcast episode #090 here.