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 ;-)

Carbohydrate Mouth-Rinses Activate Brain Areas Involved in Visual Perception & Reward - Are There Implication For Athletes & Obese Individuals You Need to Know?

CHO Mouth rinsing? Cyclist do it, but they do a lot of things ;-)

You know what a "mouth-rinse" is, right? That's when you wash some sort of liquid "through" your mouth and spit it out without swallowing. Over the past years, I have probably read a dozen of papers on this topic and although I did not keep exact record, I am pretty sure that six of them presented positive results (meaning the carbohydrate mouth-rinse increased performance), while the other six reported a null-result (no performance increase).

The former is also the main reason I did not address this topic in any previous articles in detail. A couple of days ago, I hit on a study that made me reconsider my previous decision that the contemporary evidence would suggest it's not really worth talking or rather writing about carbohydrate mouth rinses.

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The study is about to be published in the renowned pee-reviews scientific journal "Appetite" and it is the first study to replace the performance measures (physical or cognitive ones) with neuroimaging... with intriguing results, as I may say.

The good old mantra is that you ingest carbs, they are absorbed, your blood glucose levels increases and all sorts of good an bad things happen. In the course of the whole diabesity debate, here at the SuppVersity, you have already learned that this is not just an oversimplification - if it's not seen in perspective, it's simply false. Still, before the publication of the study at hand, we had only little experimental evidence of the impressive downstream effects of sweet taste receptors in the mouth.

The data Turner et al. present in their latest paper, appear to confirm that there is in fact a hitherto mostly overlooked energy signalling pathway capable of improving human performance that's triggered by the presence of carbohydrates in the mouth.

Figure 1: Performance increases (power output) observed in response to serial carbohydrate mouth rinsing during a cycle sprint - data from one of the most recent studies (Phillip. 2014)

The scientists from the University of Auckland believe that this pathway may form part of homeostatic energy systems that govern and promote feeding behaviour via the transduction of information specific to energetically-useful nutrients (Sclafani. 2004); and - as mentioned before - this pathway has already been shown to enhance corticomotor output (Gant. 2010) - the data in Figure 1 is only from one of the latest studies.

Table 1: Overview of the study results Jeukendrup et al. reviewed in their most recent overview of the literature (Jeukendrup. 2010)

Ok, the results may be inconclusive, and the dependence on exercise duration or other confounding parameters may be under-researcher, but the observed benefits are there. Being in the range of 2-4% they may seem "insignificant" (from a practical perspective, not a statistical one; see Table 1), but 4% more mileage during 1h cycling, that's worlds apart - at least in the in the world of the pro cycling. In short, The ameliorating effects CHO mouth rinses have had on the observed declines in motor function in previous studies was associated with reduced fatigue significant enough to provide a neural basis for enhancements in motor performance observed in many behavioural studies (Jeukendrup. 2010).

The protocol of the study at hand is complex, but in essence, it should suffice to know that the subjects, 10 healthy volunteers, had "mouth-rinse" with either carbohydrate (CHO) or - this is important! - a taste-matched placebo (PLA) solution in a double- blind, counterbalanced study. As the scientists point out, "[t]his protocol eliminates post-oral factors and controls for the perceptual qualities of solutions", and guarantees that the functional magnetic resonance imaging of the brain  identifies only those cortical areas which are actually responsive to oral carbohydrate during rest and activity phases of a hand -grip motor task.

Figure 2: Effect of carbohydrate on brain activity. Group level contrast images displaying areas of activation from the contrast CHO > PLA (Turner. 2014)

In particular, the scientists measure that the mean blood-oxygen-level dependent signal change experienced in the contralateral primary sensorimotor cortex was larger for CHO compared to PLA during the motor task when contrasted with a control condition. Now what's interesting is that the differences were observed not just in those areas of which we know already that they belong to the primary taste cortex.

In fact, another region that was heavily involved in the CHO mouth-rinse response was the area of the brain that's usually responsible to process visual perception, as well as regions deep down in the the limbic system that have been previously associated with reward.

How is a performance enhancing mouth rinse done? Let's take a look at the study with the largest performance leap, i.e Pottier et al. (2008):

The total rinsed/ingested amount of the solution was set at 14 mL/kg body weight and the subjects were instructed to "rinse" equally distributed over the course of the time trial. The actual rinsing lasted for 5s, afterwards the liquid hat to be spit out. The drink that was used was standard Gatoratde with 5.4 g sucrose, 0.46 g glucose, 41.7 mg Na 1 , 12.5 mg K 1 , citric acid, salt, sodium citrate, natural flavor and the other "Gatorade-ish" additives that are in there though no-one wants or needs 'em.

Bottom line: The observation of difference in both, the areas that are responsible for visual perception and the reward center are relevant for both, athletes and gymrats who are increased in maximal performance (think of a tennis player who need maximal visual acuity and enough dopamine (reward) to perform!) and overweight individuals.

The latter usually don't need a heightened visual acuity, of course. The lack of reward ... or rather their constant struggle for food-rewards on the other hand is a massive problem. In this context the superiority of the CHO vs. the artificially sweetened mouth-rinse shines a whole new light on the "diet products for weight loss debate?" and could rekindle a discussion about the timing of the measurement the dopaminergic / brain / reward response to these foods - the latter could be "instant" and any study measuring the effects in the postprandial phase may miss the most important, immediate, taste-receptor-mediated effects completely.

Plus: You want to learn more about artificial sweeteners of food reward, click on the links (RSS compatible browser required)!

References:

• Gant, Nicholas, Cathy M. Stinear, and Winston D. Byblow. "Carbohydrate in the mouth immediately facilitates motor output." Brain research 1350 (2010): 151-158.
• Jeukendrup, Asker E., and Edward S. Chambers. "Oral carbohydrate sensing and exercise performance." Current Opinion in Clinical Nutrition & Metabolic Care 13.4 (2010): 447-451.
• Phillips, Shaun M., et al. "The Influence of Serial Carbohydrate Mouth Rinsing on Power Output during a Cycle Sprint." Journal of sports science & medicine 13.2 (2014): 252.
• Pottier, Andries, et al. "Mouth rinse but not ingestion of a carbohydrate solution improves 1‐h cycle time trial performance." Scandinavian journal of medicine & science in sports 20.1 (2010): 105-111.
• Sclafani, Anthony. "The sixth taste?." Appetite 43.1 (2004): 1-3.
• Turner, Clare E., et al. "Carbohydrate in the mouth enhances activation of brain circuitry involved in motor performance and sensory perception." Appetite (2014).