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TOOLBOX: Coconut Water Magic?
Even more than training, the field of nutrition is full of commercial interests and marketing masquerading as sound “science.” One of the latest fashionable trends is drinking coconut water for health and hydration, but is it all it’s cracked up to be?



Coconut Water
This past August, I did some filming in my lab for the CBC (Canadian Broadcasting Corporation) TV show Marketplace, an investigative show which focuses on consumer affairs. This particular episode was on various superfoods, and they wanted to study whether coconut water’s hydration abilities actually matched up to their many claims.



And coconut water sales is definitely trending upwards in a big way, with a doubling of US market from 2014 ($612.5 M) to projected 2017 ($1,247.2 M). https://www.statista.com/statistics/325473/us-coconut-water-sales/

The internet is full of glowing health claims about coconut water as” Nature’s sports drink.” These include:

• Hydrates better than water.

• Full of electrolytes, especially potassium being 4x that from a banana.

• Naturally fat and cholesterol free.

• Low in calories.

Of course, all this goodness comes at a cost, namely at about $6 per litre for many popular brands of coconut water, compared to the penny or so for tap water.

The marketing on the actual packaging can be quite overblown and hyped to the max, which always gives me pause. The brand we tested actually had the tagline "Small butts – big hearts" on the packaging. Being science geeks, the joke around our lab was why the manufacturers would think that hypertrophic cardiomyopathy (a dangerous enlargement of the heart) was such a desirable selling feature...

And from a global environmental perspective, what we got to talking about during filming was the effect of the likely deforestation and monoculture farming to accommodate all of this growth in production.



Silver Hydration Bullet?
Big marketing claims, but what’s the actual evidence for any improved hydration benefits from drinking coconut water compared to plain water?

In a recent issue of the journal International Journal of Sport Nutrition and Exercise Metabolism, a research group from the UK tested the effects of coconut water on markers of hydration during submaximal exercise followed by a time trial (Peart et al. 2017). Coincidently, this study was officially published literally days after my filming with CBC. There was the experimental setup:

• 10 recreationally active males of moderate fitness took part in a repeated measures design, such that they were each tested in both a coconut water and plain water condition. As best as possible, pre-experiment diet was replicated between the conditions.

• For each trial, participants rode for 60 minutes at a moderate intensity. Besides preloading the participants with some degree of fatigue before the time trial, this set intensity protocol permitted the authors to study the physiological responses in a controlled setting with a consistent workload.

• During this set intensity workload, participants were given 250 mL of either coconut water or plain water to drink at four intervals. During the first three intervals, participants were required to drink the entire 250 mL. For the final interval, participants were allowed to drink as much or as little as they desired, and were also given the possibility of drinking more than 250 mL initially provided.

• After this initial set workload, participants then performed a 10 km time trial as quickly as possible. The only feedback received was the distance remaining.

• Ratings of perceived exertion (6-20 scale), along with first, sweetness, nausea, fullness, and stomach upset (all 1-5 scales) were asked throughout the experiment.



Cracking the Coconut Code
Overall, I felt that the study was quite well-designed and executed overall. One obvious difference is the energy intake between conditions, with no energy intake with plain water compared to 720 kJ of energy intake from consuming 1 L of coconut water. If anything, this stacks the deck in favour of coconut water.

What were the main results?

• Overall hydration status was similar between the two trials. In each, participants lost approximately 0.9% of body mass. Urine osmolality did not change over time or between conditions. Sweat rate did not significantly differ between plain water (1.19 L/h) and coconut water (1.31 L/h).

• No difference occurred in 10 km time trial performance. Plain water (966 s) was approximately five seconds faster than coconut water (971 s), but this was not significant.

• Heart rate, along with ratings of perceived exertion, did not differ at any time point between the two conditions.

• No differences were observed for blood glucose and blood lactate over the 60 minute initial ride.

• Thirst, nausea, fullness, and stomach upset did not differ between plain water and coconut water. Not surprisingly coconut water was rated as significantly sweeter than plain water. Importantly, during the final interval where participants could drink as much or as little as desired, voluntary consumption of coconut water (115 mL) was much lower than that of the plain water condition (208 mL).

Falling Down
So for anyone on the "coconut water as a superfood" bandwagon, there was no data at all in this study to support any of the claims from coconut water to be superior for hydration compared to plain water.

Any claims for coconut water benefits due to its high electrolyte content must also be taken with a proverbial grain of salt (pun intended). While coconut water is indeed very high in potassium, it must be remembered that the dominant electrolyte lost through sweat is sodium, with only trace amounts of potassium. Even in a post exercise rehydration scenario, the dominant electrolyte required for restoring fluid balance is sodium, with potassium largely of minor or minimal effect (Evans et al. 2017).

The hydration world is continually evolving in terms of best practices but, based on both the ingredients of coconut water along with studies such as this one, I doubt that any evidence will emerge in the coming years about any benefits for coconut water before, during, or after exercise.

Have fun and ride fast!

Reference
Evans GH, James LJ, Shirreffs SM, Maughan RJ (2017) Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. J Appl Physiol 122:945–951. doi: 10.1152/japplphysiol.00745.2016

Peart DJ, Hensby A, Shaw MP (2017) Coconut Water Does Not Improve Markers of Hydration During Sub-maximal Exercise and Performance in a Subsequent Time Trial Compared with Water Alone. Int J Sport Nutr Exerc Metab 27:279–284. doi: 10.1123/ijsnem.2016-0121






About Stephen:
Stephen Cheung is a Canada Research Chair at Brock University, and has published over 100 scientific articles and book chapters dealing with the effects of thermal and hypoxic stress on human physiology and performance. Stephen’s new book “Cycling Science” with Dr. Mikel Zabala from the Movistar Pro Cycling Team has just hit the bookshelves this summer, following up Cutting-Edge Cycling written with Hunter Allen.

Stephen can be reached for comments at stephen@pezcyclingnews.com .

 

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