To Spit or to Swallow - That is the Question! Carbohydrate Mouthrinse May Be Better Than Water, Yet Still Not an Option for Performance Oriented Athletes

Image 1: "You need carbs to fuel your workouts!" You know the whole litany... what may be news to you is that scientists are speculating that "intra workout carbs" do not necessarily have to be ingested to do their ergogenic magic.

Those of you, who already "friended" me on Facebook and are following what is going on on the SuppVersity Facebook page (just want to remind you that Facebook has now an option that allows you to be informed, whenever something new is posted), will probably remember the discussion revolving around "carbohydrate mouthrinsing" and whether or not it may be even more beneficial to spit and not to drink your Gatorade... now, all the health benefits of low-carbohydrate (when I am talking "low" I am not talking of Atkins type <80g) diets aside, it does seem pretty counter-intuitive that just swishing one of those carbohydrate-laden electrolyte drinks in between your teeth for a few seconds, to then spit it out again could actually have any merit. Yet, science, or I should say a handful of studies, do suggest otherwise.

As part of their recently published study into the effects of carbohydrate mouthrinsing on exercise capacity in the pre- and postprandial state (Fares. 2011), Elie-J. M. Fares and Bengt Kayser have compiled a list of the 8 hitherto published peer-reviewed papers on that subject. And if you just went by the column "increased perfomance", "yes or no", it appears like it was an established fact that carbohydrate mouthrinsing was highly ergogenic. After all, six out of the eight studies are marked with the tag "increased performance".

Figure 1: Performance increases and standard deviations of the respective measures from studies on the advantage of carbohydrate vs. artificially sweetened or plain water mouthrinse (data calculated based on summary in table 2 of (Fares. 2011)

If we do yet have a look at the quantity of those performance increases and the individual standard deviations (I compiled the respective data for you in figure 1), things begin to look less conclusive. I mean, there is obviously a standard deviation for both arms of each study and there also is a mean improvement (or decrease in performance), but if the "performance increment" is smaller than the standard deviation, for all but one study, this does make me feel uncomfortable with the statement that I would see "scientific evidence", let alone "conclusive scientific evidence" in support of carbohydrate mouth-rinses.

Mouthrinse vs. placebo = minimal (if any advantage), but what about vs. ingestion?

Regardless of what you think about the real world significance of an average performance increase of 1% (calculated based on the data from figure 1), for the small fraction of athletes for whom these minimal performance increases would actually count, i.e. high intensity endurance athletes, like time-trial Tour de France cyclists, the "control", or I should say the "benchmark" should not be plain or sweetened water, but rather one of these crab-, ah... pardon me, carb-loaden sugary electrolyte drinks these athletes are habitually consuming. I was thusly happy to see that Catherine Moss, a student of Sports and Exercise Sciences at the Massey University in Auckland, New Zealand has recently conducted an experiment for her thesis that has much more practical relevance for the high achieving athletes (Moss. 2011).

Table 1: Composition of the placebo and CHO supplement in the Moss study (adopted from Moss. 2011)

In a randomized, counter-balanced, double-blind study, Moss had eight recreationally trained cyclists perform a time trial (with a predetermined amount of work) in the course of which the cyclists ingested or rinsed (swirling 0.33ml/kg body weight of the solution for 8s) with either a placebo solution or a carbohydrate drink, whenever another 12.5% of the total work was done. In that it is worth mentioning that the composition of the CHO solutions differed for the one that was meant to be ingested and the one that was intended to be swished. With the former containing 7.5% and the latter 15% carbs, Moss mimicked solutions that had been used "successfully" previous studies. I do yet no idea, why the placebo did not contain electrolytes, as this could obviously have made a difference at least in the ingestion trials... I guess this is what distinguishes a thesis like this from a study that is worth being published in a peer-reviewed journal ;-)

Figure 2: Mean power output (in Watts) at different time points during time trial (data adapted from Moss. 2011).

As the performance data in figure 2 goes to show, only the ingestion of the carbohydrate led to significant improvements in mean power output, specifically at the later stages of the time trial. This "breakdown" may be explained by the "glycogen reduction exercise protocol" all participants had conducted the day before the time trial. So that after a "low carbohydrate" dinner, the participants were supposed to be glycogen depleted when they performed the time-trial on the subsequent morning.

Figure 3: Total time (in s) during time trial (data adapted from Moss. 2011).

In a way this is an unfair advantage, for the carb ingestion, which accordingly elicited way better time trial times. It does yet not lessen the significance of data on carbohydrate vs. water mouth rinse, which shows pretty conclusively that in a glycogen depleted state both forms of mouthrinsing (plain water or a 15% carbohydrate solution) are equally ineffective, when it comes to actual performance increases.

Figure 4: Pleasure / displeasure feeling during time trial (data adapted from Moss. 2011).

If you do however look at the pleasure/displeasure feeling scale data in figure 4, I would speculate that in a non-glycogen depleted state the carbohydrate-rinsers would have performed significantly better... I mean, without gas in the tank a car won't work even if it "wanted". In view of the fact that the carbohydrate ingestion group did yet pedal at a higher intensity, this would warrant further investigation.

Figure 5: Respiratory exchange ratio (higher values = higher carbohydrate oxidation) during time trial (data adapted from Moss. 2011).

That being said, there was what I consider an interesting effect of carbohydrate rinsing on the respiratory exchange ratio (remember higher values = higher carb oxidation), which would suggest that the theory Fares and Kayser propose (Fares. 2011), according to which the activation of sweetness taste receptors cells (T1R2 and T1R3) in the mouth would explain the previously cited performance "increases" in other studies, may have its merits. What else than the sensation of incoming carbs could explain that the cyclists burned more carbs in the carb mouthrinse compared to the placebo mouthrinse trial (cf. figure 5) - and that in the absence of significant differences in blood glucose or insulin levels?

Spit it or suck it? What's right for you?

While we do not know whether it would make sense to mouthrinse in a glycogen repleted state (yeah, I know +1% ;-), for any athlete interested in maximal performance, simply ingesting his carb + electrolyte drink would certainly be the best option. The (intermittendly) fasting dieter, who wants to maximize his fatty acid oxidation in the course of say his "morning cardio", on the other hand, would be best off with a non-carby electrolyte drink that helps him avoid dehydration and does not compromise (even if the effect is minimal) fatty acid oxidation... what? You want to know who would  benefit from spitting his carbs out? Well, at least based on the current data, mostly the cleaning contractors of your local gym - after all, they would have to work overtime (and be paid overtime) to clean up the mess ;-)