IMPORTANT! YOU MUST READ THIS BEFORE CONTINUING:
by Ron Brown, Ph.D., author of The Body Fat Guide
read Dr. Oz's newspaper column, in which he and his partner Dr. Roizen
questioned coconut water as a sports drink because of the high amount of sodium
it contained, red flags immediately appeared in my mind. I have been using
coconut water, one of the healthiest drinks in nature, and recommending coconut
water fresh from young coconuts for some time, and I have never detected an
alleged high sodium content in coconut water. What was Dr. Oz talking about?
So, I went to the USDA Database of Nutrients to double check the nutrient facts on coconut water. To my surprise, I found that the USDA nutrient values perfectly matched the values reported by Dr. Oz and Dr. Roizen for coconut water, including a 250 mg value for sodium per cup. Could this be true? Did coconut water consumption really pose a hidden health risk from high sodium content in addition to the benefits I had read about? Was coconut water no longer a worthy candidate as the ultimate sports drink to naturally replenish important electrolytes like calcium and potassium?
I immediately recalled an article in a peer-reviewed journal that described how coconut water was used intravenously for medical emergencies (Campbell-Falck, Thomas, Falck, Tutuo, & Clem, 2000). I looked up the article and noticed it contained a table of coconut water composition with listings from various researchers. So I double checked the calculations for sodium content.
In the table for coconut water in the article, mEq/L values for sodium are listed as 5.0, 4.2, 0.7, 5.0, 4.0, 2.9, 9.7. If we throw out the high and low values (outliers), the mean value for sodium is 4.22 mEq/L. To convert from mEq/L to mg/L you multiply mEq/L by the atomic weight of the molecule and divide the product by its valence. One mEq of sodium has an atomic weight of 23 mg and a valence of 1, times 4.22mEq/L equals about 97 mg of sodium per liter of coconut water, or only about 23 mg of sodium in one cup of coconut water, not 250 mg reported by Dr. Oz. Dr. Oz was off by over 10 times the actual amount of sodium in coconut water!
In fairness to Dr. Oz, the USDA Database seems to be the real culprit. How could the USDA report such a large difference in sodium values? Did the USDA use different types of coconuts to analyze coconut water? Actually, yes! A likely explanation is that Dr. Oz confused the USDA analysis of water in mature coconuts with the more popular coconut water from young coconuts. Campbell-Falck et al. noted that "because the younger coconuts contain more fluid, these are generally chosen for intravenous fluid administration." As the fluid content reduces in mature coconuts, it may be that the nutrient concentration of minerals like sodium in the water increases compared to coconut water from young coconuts.
The inconsistency isn't just with the USDA's values for sodium in coconut water. USDA values for calcium (Ca2+) and especially for phosphate (PO43–) in coconut water are also questionable. Performing similar calculations on calcium in coconut water (atomic weight: 40.1 and valence: 2) and phosphate (atomic weight: 94.97 and valence: 3) from data reported in Campbell-Falck et al. (2000) reveals that there are approximately 21.6 mg of calcium and 11.4 mg of phosphorus in 100 ml or about 100 grams of coconut water. Although this calculated calcium value is close to the USDA's value, the phosphorus value is almost half the amount of phosphorus reported by the USDA, which originally showed almost equivalent levels of calcium and phosphorus.
The USDA's numbers are further contradicted by Campbell-Falck et al. (2000) who noted coconut water's "high potassium, calcium, and magnesium content," and that "sodium, chloride, and phosphate are found in much lower concentrations." The startling conclusion from an analysis of data in the article by Campbell-Falck et al. is that coconut water actually has a very healthy bone-building calcium: phosphorus ratio of 1.89:1, which is 45% greater than cow milk!
One final word of warning: All commercially packaged, non-refrigerated coconut water is pasteurized by ultra high temperature (UHT) processing. According to the Food and Agriculture Organization of the United Nations, this heat process "destroys some of coconut water's nutrients and almost all the flavour." So get your clean, safe, nutritious, and tasty coconut water directly from young coconuts. Avoid young coconuts that are not fresh. Researchers from the University of the West Indies discovered that when young coconuts are harvested and allowed to drop to the ground, the inner shell may crack and increase spoilage.
UPDATE, February 11, 2014:
The USDA now lists unsweetened coconut water beverage containing 59 mg sodium per cup, as well as 28 mg calcium and 16 mg phosphorus per cup, which is significantly closer to the values in the Campbell-Falck et al. study than to the sodium value reported by Dr. Oz.
Campbell-Falck, D., Thomas, T., Falck, T. M., Tutuo, N., & Clem, K. (2000). The intravenous use of coconut water. American Journal of Emergency Medicine, 18, 108–111.
Food and Agriculture Organization of the United Nations. (2007). How to bottle coconut water. Retrieved from http://www.fao.org/ag/magazine/0701sp1.htm