I can’t speak for the rest of the country, but the city of Austin is currently cuckoo for coconut water. It’s in every health food store, supermarket and gas station, and people can’t shut up about its purported heath benefits – “more hydrating than water”, “more potassium than a banana” and the well-worn ambiguous standard, “boosts your immune system”. Personally I prefer to stave off dehydration with a more traditional 2:1 mixture of hydrogen and oxygen, but it’s nice to see people drinking something other than soda and I’m certainly not out to rain on civilization’s latest nutritional fad parade. However, I did hear one claim about coconut water that seemed to require my immediate investigation. Here is the rumor as it was told to me, “During WWII, coconut water was used for emergency transfusions during times when blood (or proper blood type) was in short supply. It worked because coconut water is isotonic to blood.”
Isotonic is a fun word to say at parties, and a useful property when one wishes to avoid having cells shrivel or explode (the consequence of being immersed in fluid of too high or too low solute concentration) but this hardly seems like it would prevent someone from bleeding to death. The quality that we most enjoy about blood isn’t that it takes up space in our veins and arteries, but that it contains hemoglobin, which transports oxygen to our various organs. To my knowledge, coconuts lack this vital ingredient. Furthermore, I argued when the tale was relayed to me, the only thing rarer than type O negative blood* would surely be a coconut in the middle of Europe prior to the era of wide-scale shipping of produce. Doubts aside, I typed “coconut water blood transfusion” into my search engine and was greeted with a large number of hits, as well as a much-needed reminder that WWII was fought not only in Europe, but also in the Pacific, where doctors would conceivably have access to coconuts.
Not surprisingly, medical literature yielded no reports of coconut water functioning as a suitable substitute for blood. However, I did find documentation of the fluid being successfully used for emergency hydration in locations where the usual sterile IV saline solution was unavailable and coconuts were plentiful. Immature coconuts are the best choice for IV hydration as they contain the most liquid, or coconut water. Coconut “milk”, it turns out, is not the fluid inside a coconut, but rather an emulsion made from the grated coconut meat. So please take a moment to replace your mental image of the iconic bark-like brown coconut with a young green one and please envision its interior as an almost clear whitish fluid rather than the opaque syrupy stuff you use to make curry. Coconut water is actually hypotonic to blood plasma (that is, it has lower solute concentration) and more acidic. It also contains far less sodium and far more potassium than either plasma or saline solution. It is therefore a non-ideal IV hydration fluid. Nonetheless, it is seems to work in a pinch, as a Solomon Island patient who received the coconut IV treatment was reported to have eventually left the hospital without any peculiar complications.
As for the lighter claims about coconut water, it’s potassium content relative to a banana is easy enough to establish. The 14 oz bottle of coconut water I purchased while researching this article boasted 569 mg of potassium, whereas a banana is estimated to contain somewhere around 450 mg. But, as noted above, high potassium content is not a desirable quality for IV hydration. Excessive potassium in blood can even cause a condition called hyperkalemia, which can in extreme cases be fatal.
Aptitude for (oral) hydration is a bit harder to establish, but luckily somebody did bother to design an experiment comparing coconut water to regular water and also to “carbohydrate-electrolyte beverage” (Gatorade and its ilk) †. Subjects ran on a treadmill and then consumed of 1 of the 3 beverage types. Here coconut water fared better than plain water, although so did the Gatorade. Part of the advantage is that people can choke down more coconut water or sport beverage than they can plain water. Optimum post-exercise rehydration is achieved by consuming liquid amounting to 120% of what was lost through sweating. That’s potentially a lot of water (about 1 liter per hour), especially when exercising in hot environments. The electrolytes in coconut water and sports drinks help maintain the sensation of thirst, so people keep drinking them past the point where they would have put down the water bottle. Additionally, subjects drinking plain water were more likely to report nausea during the rehydration period. The coconut water drinkers also reported experiencing less stomach upset and feelings of fullness than either plain water or sport beverage drinkers.
If you ask me, coconut water tastes funny. The hydration article participants claimed it tasted sweet (it does have a higher glucose content than plain water, which has none) but I found it somewhat salty. In fact, it tasted rather like how I imagine bottled sweat would taste, which is hardly the makings of a desirable beverage. The bottle I purchased languished in my refrigerator awaiting mixers until a friend offered to add it to a breakfast smoothie. Perhaps the stuff tastes better during a hydration emergency, but it didn’t stick around long enough to find out.
* In actuality, AB- is the rarest blood type in the human population. However, you probably think O- is the rarest and I didn’t want to confuse or disappoint you. O- is still fairly uncommon. Additionally, O- is the “universal donor” and patients with this blood type cannot be transfused with any other type, thus its rarity is potentially more problematic. The AB- people can make do with a number of other blood types.
† Electrolytes aren’t just some word made up by sports drink manufacturers. They’re ions in solution and are critical to a variety of cellular activity. Sodium and chloride are the predominant ions in blood plasma, whereas coconut water is heavy on potassium, calcium and magnesium.
Who Told You This?
Campbell-Falck, D. et al. 2000. “The Intravenous Use Of Coconut Water.” American Journal of Emergency Medicine 18: 108-111.
Pummer, S. et al. 2001. “Influence of Coconut Water on Hemostasis.” American Journal of Emergency Medicine 19: 287-289.
Saat, M. et al. 2002. “Rehydration after Exercise with Fresh Young Coconut Water, Carbohydrate-Electrolyte Beverage and Plain Water.” Journal of Physiological Anthropology 21(2): 93-104.