Content uploaded by Douglas Kalman
Author content
All content in this area was uploaded by Douglas Kalman on Aug 01, 2014
Content may be subject to copyright.
Content uploaded by Douglas Kalman
Author content
All content in this area was uploaded by Douglas Kalman on Aug 01, 2014
Content may be subject to copyright.
Available via license: CC BY 2.0
Content may be subject to copyright.
RESEARCH ARTICLE Open Access
Comparison of coconut water and a
carbohydrate-electrolyte sport drink on measures
of hydration and physical performance in
exercise-trained men
Douglas S Kalman
1
, Samantha Feldman
1
, Diane R Krieger
1
and Richard J Bloomer
2*
Abstract
Background: Sport drinks are ubiquitous within the recreational and competitive fitness and sporting world. Most
are man ufactured and artificially flavored carbohydrate-electrolyte beverages. Recently, attention has been given to
coconut water, a natural alternative to manufactured sport drinks, with initial evidence indicating efficacy with
regard to maintaining hydration. We compared coconut water and a carbohydrate-electrolyte sport drink on
measures of hydration and physical performance in exercise-trained men.
Methods: Following a 60-minute bout of dehydrating treadmill exercise, 12 exercise-trained men (26.6 ± 5.7 yrs)
received bottled water (BW), pure coconut water (VitaCoco
®
: CW), coconut water from concentrate (CWC), or a
carbohydrate-electrolyte sport drink (SD) [a fluid amount based on body mass loss during the dehydrating
exercise] on four occasions (separated by at least 5 days) in a random order, single blind (subject and not
investigators), cross-over design. Hydration status (body mass, fluid retention, plasma osmolality, urine specific
gravity) and performance (treadmill time to exhaustion; assessed after rehydration) were determined during the
recovery period. Subjective measures of thirst, bloatedness, refreshed, stomach upset, and tiredness were also
determined using a 5-point visual analog scale.
Results: Subjects lost approximately 1.7 kg (~2% of body mass) during the dehydrating exercise and regained this
amount in a relatively similar manner following consumption of all conditions. No differe nces were noted between
coconut water (CW or CWC) and SD for any measures of fluid retention (p > 0.05). Regarding exercise
performance, no significant difference (p > 0.05) was noted between BW (11.9 ± 5.9 min), CW (12.3 ± 5.8 min),
CWC (11.9 ± 6.0 min), and SD (12.8 ± 4.9 min). In general, subjects reported feeling more bloated and experienced
greater stomach upset with the CW and CWC conditions.
Conclusion: All tested beverages are capable of promoting rehydration and supporting subsequent exercise. Little
difference is noted between the four tested conditions with regard to markers of hydration or exercise
performance in a sample of young, healthy men. Additional study inclusive of a more demanding dehydration
protocol, as well as a time trial test as the measure of exercise performance, may more specifically determine the
efficacy of these beverages on enhancing hydration and performance follo wing dehydrating exercise.
Keywords: Hydration, Coconut Water, Sport Drink, Exercise
* Correspondence: rbloomer@memphis.edu
2
The University of Memphis, Cardiorespiratory/Metabolic Laboratory,
Department of Health and Sport Sciences, 106 Roane Fieldhouse, Memphis,
TN 38152
Full list of author information is available at the end of the article
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
© 2012 Kalman et al; licensee BioMed Central Ltd . This is an Open Access article distributed under the terms of the Cr eative Commons
Attribution License (http://c reativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and rep roduction in
any medium, provided the original work is properly cited.
Background
Fluid loss during strenuous, long duration exercise is
commonplace and can result in thermal stress, impaired
cognition and cardiovascular function, accelerated fati-
gue, and impaired exercise performance [1,2]. Recom-
mendations for fluid intake before, during, and following
exercise are well d escribed [3,4] and are typically fol-
lowed by m ost athletes seeking enhanced physical per-
formance. Abiding by such recommendations appear s
particularly important when exercising in hot and
humid environmental conditions, where fluid loss ma y
be high [5].
Although water is often suggested to many general fit-
ness enthusiasts who may exercise for relatively short
periods of time ( < 75 minutes), carbohydrate-electrolyte
sport drinks are highly recommended and appear to be
the beverage of choice fo r most serious athletes –aerobic
athletes in particular [2]. This is partly fueled by scienti-
fic recommendations for the consumption of such bev-
erages [6,7], and partly by the widespread marketing
campaigns of l arge sport nutrition and beverage compa-
nies. Regardless, carbohydrate-electrolyte beverages are
widely consumed and represent a multi-billion dollar
segment of the food and beverage industry [8].
Some individuals prefer natural alterna tives to the
manufactured sport drinks. For exa mple, many sport
drinks contain fructose and/or maltodextrin, artificia l fla-
vors and sweeteners, and added electrolytes (e.g., sodium,
potassium). With more emphasis recently within the
sport nutrition industry on “natural” beverages, some
athletes and recreationally active fitness enthusiasts seek
alternatives to the manufactured sport drink. While
water is indeed a reasonable solution for some, those
involved in longer duration exercise bouts often require
and demand carbohydrate and electrolytes within their
beverage of choice. For these individuals, coconut water
may be considered as one viable alternative.
Coconut water is naturally occurring, is very rich in
potassium, contains sodium, chloride, and carbohydrate
[9], and is viewed as the hydrating beverage of choice in
certain parts of the world [10 ]. Clinically, co conut water
may be used as an oral rehydration aid t o replace fluid
loss from the gastrointestinal tract in patients suffering
severe dehydration due to diarrhea [11,12]. It has also
been used intra venously with success [13]. Although not
linked specifically to hydration, coconut water has been
reported to have antioxidant properties [14], which may
aid in neutralizing reactive o xygen species production
resulting from long duration exercise [15].
In relation to sport nutrition, coconut water has been
reported to provide hydrating effects similar to those o f
carbohydrate-electrolyte sport drinks [16-18]. Unfortu-
nately, these studies have focused exclusively on
hydration measures as primary outcome variables (fol-
lowing a period of dehydrating exercise and consump-
tion of the assigned beverage ), while not emphasizing
actual exerc ise perf ormance during the rehydrating per-
iod. He nce, while the rehydrating effects of coconut
water may be similar to t hose of carbohydrate-electro-
lyte sport drinks, an equally impo rtant question for
most athletes and coaches is whethe r or not the hydra-
tion status equate s to actual physi cal performance. Con-
sidering the above, we investigated the effects of two
different forms of coconut water (concentrated and not
from concentrate) and a carbohydrate-electrolyte sport
drink on measures of hydration status and physical per-
formance in exercise-trained men.
Methods
Subjects and Screening
Exercise-tr ained men were recruited to participate. Elig-
ibility was determined by completion of a health history
form (Physical Activity Readiness Questionnaire [PAR-
Q]) and physical examination. Prior to the start of the
study, subjects were engaged in a program of regular
exercise for a minimum of the past six months, without
difficulty in walking or running on a t readmill. All sub-
jects were instructed to maintain their pre-study exer-
cise program thro ughout the course of the study, with
the exception of refraining from exercise during the 24
hour s pr ior to e ach test day. Subjects were nonsmokers,
did not report any history of cardiovascular, metabolic,
neurological, or orthopedic disorders that may have
impacted their ability to participate in the study, and
did not start the use of any new nut ritional supplement
over the course of the study; however, they were allowed
to continue using nutritional supplements they had been
using prior to beginning the study (e.g., multivitamins).
Prior to participation, each subject was informed of all
procedures, potenti al risks, and benefits associated with
the study through both verbal and written form in
accordance with the approved procedures of the Aspire
Institutional Review Board for Human Subjects Research
(La Mesa, CA; approval date of December 23, 2010).
Subjects signed an informed consent form prior to
being admitted into the study.
At the initial screening visits, subjects’ height via stadi-
ometer (Holtain Limited; Britai n) and body mass via
digital scale (Detecto; Webb City, MO) were measured
and recorded. Body mass was obtained with subjects
wearing only a gown and their underwear. Body mass
measures following exercise were obtained o nly after
subjects were thoroughly towel dried. Heart r ate and
blood pressure (using subjects ’ left arm) were recorded
following a minimum of five minutes of quiet rest, while
subjects were seated in a chair. A 12-lead
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 2 of 10
electrocardiogram was obtained and analyzed for nor-
mality, to ensure subject suitability for participation.
Blood samples were collected from subjects for routine
assessment of clinical chemistry parameters ( e.g., meta-
bolic panel and comp lete blood count). Pleas e see Table
1 for subject descriptive characteristics. A familiarization
trial of the exercise performance test was also conducted
during the initial laboratory visit. A description of this
test is provided below.
Test Days
On each of the four test days, subjects reported to the
lab in the morning following an o vernight fast (no food
or beverages other than water were allowed after mid-
night). The time of day for testing each subject was
matched for all subsequent test days ( ± 60 minutes).
Subjects were instructe d not to exercise or to consume
alcohol during the 24 hours prior to each test day, but
to consume water liber ally up to the time they reported
to the lab for testing. Adherence to study instructions
was confirmed with all subjects on each day of testing.
Following all baseline assessments, subjects were pro-
vided with a standardized breakf ast co nsisting of a bagel
and one tablespoon of cream cheese. They were also
provided with up to 470 mL of water.
Dehydrating Exercise Test
Sixty minutes following the conclusion of the s tandar-
dized breakfast, subjects performed the dehydrating exer-
cise test. It should be noted that of the total of 48 test
visits (12 subjects × 4 visits), slight deviations in the time
from food intake to the start of the dehydrating exercise
test were noted for 14 of the tests (i.e., started before or
after the set 60 minute time). Specifically, nine tests were
conducted wi thin 15 minutes of this time, two tes ts were
conducted within 30 minutes of this time, and three tests
were conducted within 45 minutes of this time. We do
not believe these deviations signifi cantly influence d the
findings; in particular considering that these were equally
dispersed among the four conditions.
The dehydrating exercise consisted of two, 30-minute
bouts of walking/jogging, interspersed with a 10 minute
rest period. Specifically, subjects walked/jogged at 2, 3,
4, 5, 6 and 7 miles per hour on a motorized treadmill,
using a grade of 0%. Five minutes of exercise was per-
formed at each speed. Following the initial 30 minutes
of exer cise, a 10-min ute b reak was al lowed, during
which time subjects walked around and/or remained
seated. Subjects then repeated the above sequence of
speeds f or an additional 30 minutes of exercise. Hence,
a t otal of 60 minutes of exercise was performed within
the70minuteperiod.Allexercisewasperformedina
climate controlled room, with an average temperature of
36° Celsius and an a verage relative humidity of 48%.
This dehydrating ex ercise protocol has been reported to
induce a 2 to 3% reduction in body weight [19]. During
the three hour period f rom the end of th e dehydrating
exercise test to the start of the performance exercise
test, subjects were required to rest quietly without food
or beverage intake (with the exception of the assigned
condition). During this time, as well as during the per-
formance exercise test, subjects remained in a thermo-
neutral environment (i.e., 22 degrees Celsius).
Conditions
Within minutes following the conclusion of the dehy-
drating exercise test (after all measurements were
Table 1 Characteristics of 12 exercise-trained men
Variable Value
Age at Screening (years) 26.6 ± 5.7
24.0 (21.0 - 35.0)
Ethnicity
Hispanic 12 (100%)
Total 12 (100%)
Race 12 (100%)
Caucasian 12 (100%)
Total 12 (100%)
Height (cm) 175.4 ± 4.1
175.0 (168.6 - 181.2)
Body Mass at Screening (kg) 77.2 ± 6.3
78.4 (66 - 85.8)
Body Mass Index (kg ∙ m
-2
) 25.1 ± 1.8
26.1 (21.5 - 26.9)
Systolic Blood Pressure (mm Hg) 118.4 ± 13.2
120.5 (97.0 - 145.0)
Diastolic Blood Pressure (mm Hg) 73.9 ± 6.7
74.0 (64.0 - 87.0)
Heart Rate (beats ∙ minute
-1
) 68.8 ± 14.4
66.5 (48.0 - 99.0)
Glucose (mg ∙ dL
-1
) 92.5 ± 4.0
91.5 (87.0 - 99.0)
Blood Urea Nitrogen (mg ∙ dL
-1
) 15.2 ± 3.0
16.0 (9.0 - 19.0)
Creatinine (mg ∙ dL
-1
) 1.0 ± 0.2
1.0 (0.7 - 1.2)
Alkaline Phosphatase (Units ∙ L
-1
) 82.0 ± 41.0
73.0 (32.0 - 177.0)
Aspartate Amino Transaminase (Units ∙ L
-1
) 21.4 ± 4.4
20.5 (16.0 - 29.0)
Alanine Amino Transferase (Units ∙ L
-1
) 20.8 ± 5.8
21.0 (11.0 - 30.0)
White Blood Cell count (thousands ∙ μL
-1
) 6.9 ± 1.7
6.7 (4.2 - 9.8)
Red Blood Cell count (millions ∙ μL
-1
) 5.3 ± 0.4
5.3 (4.5 - 6.1)
Hemoglobin (g ∙ dL
-1
) 15.0 ± 1.0
15.3 (13.1 - 16.0)
Hematocrit (%) 47.7 ± 3.0
47.9 (42.8 - 52.2)
Data are mean ± SD (top row); median and (range) provided in bottom row
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 3 of 10
obtained–see Table 2), s ubjects received their assigned
condition (beverage). The s tudy design involved a r an-
dom order, single blind (subject and not investigators),
cross-over assignment to one of the foll owing four con-
ditions: Supermarket brand bottled water, pure coconut
water (VitaCoco
®
;NewYork,NY),coconutwaterfrom
concentrate, or a carbohydrate-electrolyte sport drink
(5-6% carbohydrate solution). The amount of each bev-
erage was determined based on the total amount of
body mass lost during the dehydrating exercise protocol
using the equation: 130 0 mL ∙ kg
-1
× k g loss = amount
of beverage consumed (mL). This provided a weighted
volume amount of beverage equal to approximately
125% of the actual body mass lost. Based on this, the
amount of beverage c onsumed equate d to 2159 ± 24 9
mL for b ottled water, 2220 ± 367 mL for VitaCoco
®
,
2253 ± 358 mL for coconut water from concentrate,
and 2184 ± 358 mL for the sport drink, with no differ-
ences n oted between conditions (p > 0.05). Subjects
were allowed 60 minutes to consume the entire volume
of b everage. Each condition was co nsumed on a differ-
ent test day, with a minimum of five days separating
test visits.
Performance Exercise Test
Three hours after the completion of the dehydrating
exercise test (and two hours after subjects consumed
their assigned condition), a test of physical performance
was conducted using a treadmill as previously done [20].
Specifically, subjects began walkin g on a motorized
treadmil l at a self-selected comfortable speed (0% grade)
for five minutes. At the conclusion of the five-minute
period, the actual performance test began. Th e protocol
involved an increase i n intensity every three minutes.
While the speed of the treadmill remained constant at
4.2 miles per hour throughout the test, the grade
increase in the following manner: min 1-3, 0%; min 4-6,
2.5%; min 7-9, 5%; min 10-12, 7.5%; min 13-15, 10%;
min 16-18, 12.5%; min 19-21, 15%. S ubjects ex ercised
until volitional exhaustion and the total exercise time
was recorded. This identical protocol was administered
at the screening visit (for familiarization) and on each of
the four test day visits. Therefore, we do not believe
that there was any significant degree of “learning”
involved with this test.
Outcome Measures
In addition to the measure of total exercise time
obtained in the performa nce test described above, the
following variables were used as outcome measures;
some of which have been discussed previously [21].
With regard to hydration status, body mass, fluid reten-
tion (based on body mass), plasma osmolality, and urine
specific gravity were measured. Specifically, for fluid
retention based on body mass, it was expected that the
administration of test product at the amount prescribed
would bring the subject’s body mass back to very near
its pre-exercise level. The rehydrating efficacy of the test
product w as indicated by how well this volume of fluid
was retained over the two hours following consumption.
Therefore, the body mass immediately post beverage
consumption (which occurred at 1 hour post dehydrat-
ing exercise) was considered the “baseline"; this was sub-
tracted from the body mass values at 2 and 3 hours post
dehydrating exercise, and this difference was divi ded by
the mass of beverage that had been consumed, then
multiplied by 100 to yield the “percent of rehydrating
fluid retained” at 2 and 3 hours. It should be noted that
Table 2 Study timeline and outcome measures
Time ®
Variable ↓
Pre
Dehydrating
Exercise Test
Immediately Post
Dehydrating Exercise
Test
1 Hour Post
Dehydrating
Exercise Test
2 Hours Post
Dehydrating
Exercise Test
3 Hours Post
Dehydrating
Exercise Test†
Immediately Post
Performance Exercise
Test
Body
Mass††
X X* X** X X
Plasma
Osmolality
XX X
Urine
Specific
Gravity
XX X
Subjective
Measures
(VAS)
XXXX
Heart Rate X X X X
Blood
Pressure
XX X X
† The Performance Exercise Test began following this measur ement time (total exercise time was reco rded)
†† Body Mass was used to calculate fluid retention (as described in the Methods section)
* For determination of fluid volume to consume
** For determination of “baseline” body mass
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 4 of 10
body mass was ac curately dete rmined using a n electro-
nic scale with subjects dry and wearing only a gown and
underwear. In additional, all fluid volumes delivered to
subjects were meticulously m easured. Our use of body
mass was used as a surrogate efficacy indicator of hydra-
tion as done previously [22].
Plasma osmolality and urine specific gravity were
determined using standard procedures. Osmolality was
determined by freezing point depression. Specific gravity
was determined using reagent test strips. Although we
did not measure urine osmola lity, it has been concluded
by Arms trong and colleagues that “urine osmolality and
urinespecificgravitymaybeusedinterchangeablyto
determine hydration status” [23]. Both plasma osmolality
and urine specific gravity have been used previously as
indicators of hydration status [24], and were obtained
prior to the dehydrating exercise test, immediately fol-
lowing the dehydrating exercise test, and prior to the
performance exercise test.
With regard to subjective measures, t hirst, bloate d-
ness, refreshed, stomach upset, and tiredness were
determined using a 5-point visual analog scale. Answers
were scaled from 1 to 5 where 1 was the lowest and 5
was the highest score. These were assessed immediate ly,
60 min utes, 120 minutes , and 180 minutes following the
dehydrating exercise test.
Heart rate and blood pressure were measured at the
following times: Prior to the dehydrating exercise test,
immediately following the dehydrating exercise test,
prior to the performance exercise test, and immediately
following the performance exercise test. A schematic of
the study timeline fo r all outcome measures is provided
in Table 2.
Physical Activity and Dietary Intake
Subjects were instructed to maintain their normal physi-
cal activity throughout the study period, with the exc ep-
tion of refraining from strenuous physical activity
during the 24 hours preceding each test day. They were
also given specific instructions rega rding abstinence
from alcohol consumption during the 24 hours immedi-
ately preceding the test days. Dietary intake was to be
maintained through the study period, with the exception
of reporting to the lab in a fasted state on each of the
four test days. No food records were maintained in this
study, which may be consi dered by some to be a limita-
tion of this work.
Statistical Analysis
The sample size was determined based on convenience
and a power analysis was carried out to determine the
effect sizes that would provide an 80% chance of obtain-
ing a significant result of p ≤ 0.05, when testing the out-
come measures using the paired Student t test. Using a
sample of 12 subjects, an 18% difference in fluid reten-
tion between products wo uld be needed to detect statis-
tical significance. All numerical vari ables were te sted for
normality by the Anderson-Darling test. Outcome mea-
sures as described within the text above for each vari-
able, at each time point, were analyzed by the paired
Student t test. All analyses were performed using “R“
statistical software (version 2.13.1; R Foundation for Sta-
tistical Computing). Statistica l signi fica nce was set at p
≤ 0.05. The data are presented as mean ± SD.
Results
Overview and Adverse Effects
All subjects successfully completed all aspects of this
study, with the exception of one subject who was unable
to consume the volume of coconut water from concen-
trate in the allotted time. Therefore, the trial for this
subject was not included in the analysis (n = 11 for
coconut water from concentrate). Very few adverse
events were no ted and all were characterized as mild (e.
g., stomach upset), likely due t o the consumption of a
high volume of fluid ( > 2 liters) in a relatively short
period of time (≤ 60 minutes).
Performance Data
Regarding treadmill performance, no significant differ-
ence (p > 0.05) was noted in total exercise time between
bottled water (11.9 ± 5.9 m inutes), VitaCoco
®
(12.3 ±
5.8 minutes), co conut water from concentrate (1 1.9 ±
6.0 minutes), and sport drink (12.8 ± 4.9 minutes).
Hydration Data
In regard to body mass, subjects lost approxima tely 1.7
kg during the dehydrating exercise (~2% of starting
body mass), regained this amount in a similar manner
following consumption of all conditions, and slowl y lost
approximately 1 kg over the subsequent two hours
(Table 3). However, body mass (p = 0.023) was slightly
greater with coconut water from concentrate compared
only to bottled water (when expressed as change from
pre dehydrating exercise at 3 hours post dehydrating
exercise). No other differences were noted between con-
ditions for body mass (p > 0.05). In regard to fluid
retention (based on body mass), similar findings were
observed (as this measure is influenced by body mass),
with greater values for coconut wa ter from concentrate
compared only to bottled water (p = 0.041) at 3 hours
post dehydrating exercise. At 3 hours post dehydrating
exercise (2 hours after rehydration) values were numeri-
cally highest for coconut water from concentrate
(~52%), lowest for bottl ed water (~35%), and intermedi-
ate for VitaCoco
®
and sport drink (~40%); although
these differences were not statistically significant (p >
0.05). No other differences were noted between
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 5 of 10
conditions for fluid retention (p > 0. 05). Data are pre -
sented in Table 4. Plasma osmolality displayed similar
results as note d for body mass and fluid retention, with
greater values for coconut wa ter from concentrate com-
pared only to bottled water (p = 0.049; when expressed
as change from pre dehydrating exercise at 3 hours post
dehydrating exercise). In general, this measure increased
after d ehydrating exercise, indicating dehydration of the
subjects, and returned toward baseline at 3 hours post
dehydrating exercise, indicating rehydration of the sub-
jects. No other differences were noted between condi-
tions for plasma osmolality ( p > 0.05). Data are
presented in Table 5. No differences were noted
between conditions for urine specific gravity, with this
measure relatively constant and within the normal range
over the measureme nt period (p > 0.05). Data are pre-
sented in Table 6.
Subjective Data
All four conditions quenched thirst with no significant
differences between conditions (p > 0.05). Subjects
reported fe eling bloated with all four conditions, as per
statistically significant increases at 1 hour post dehydrat-
ing exercise. Over the two hour rehydration period, the
bloatedness decreased for all four conditions but
remained statistically significant at 3 hours post dehy-
drating exercise for VitaCoco
®
(p = 0.012) and coconut
water from concentrate (p = 0.034). Subjects generally
felt refreshed after rehydration, with a statistically signif-
icant increase for bottled water over VitaCoco
®
at 1
hour post dehydrating exercise (p = 0.036). No other
differences were noted (p > 0.05). The two coconut-
based products tended to produce more stomach upset
than bottled water or sport drink, with significant find-
ings at 3 hours post dehydrating exercise for VitaCoco
®
and sport drink (p = 0.034), VitaCoco
®
and bottled
water (p = 0.046), coconut water from concentrate and
sport drink (p = 0.020) and coconut water from concen-
trate and bottled water (p = 0.020). Tiredness generally
tended to decrease immediately post dehydrating exer-
cise, with no significant differences betwe en conditions
(p > 0.05). All subjective data are presented in Table 7.
Heart Rate and Blood Pressure Data
No differences were noted between conditions for heart
rate, systolic blood pressure, or diastolic blood pressure
(p > 0.05). Data for these variables are presented in
Table 8.
Table 3 Body mass of exercise-trained men before and after dehydrating exercise
Time VitaCoco
®
Sport Drink Coconut Water
From Concentrate
Bottled Water
Pre Dehydrating Exercise 78.5 ± 7.4
79.2 (65.2 - 89.0)
77.8 ± 7.1
78.2 (65.2 - 87.3)
77.5 ± 7.6
75.6 (64.9 - 88.4)
77.8 ± 7.6
78.2 (64.8 - 89.3)
Immediately Post
Dehydrating Exercise
76.9 ± 7.2
77.4 (63.9 - 87.2)
76.1 ± 6.8
76.6 (63.8 - 85.3)
75.8 ± 7.5
73.7 (63.3 - 86.5)
76.2 ± 7.4
76.5 (63.5 - 87.4)
1 hour Post
Dehydrating Exercise
78.4 ± 7.3
79.0 (65.5 - 88.9)
77.7 ± 7.2
77.8 (65.1 - 87.6)
77.6 ± 7.6
75.5 (65.0 - 88.6)
77.9 ± 7.6
78.1 (64.9 - 90.1)
2 hours Post
Dehydrating Exercise
78.1 ± 7.2
78.3 (65.5 - 88.8)
77.4 ± 7.0
77.6 (65.1 - 87.0)
77.3 ± 7.5
75.2 (64.8 - 88)
77.4 ± 7.5
77.6 (64.7 - 88.9)
3 hours Post
Dehydrating Exercise*
77.6 ± 6.9
78.0 (65.5 - 87.9)
77.0 ± 6.8
77.2 (64.9 - 86.3)
76.9 ± 7.4
75.0 (64.6 - 87.6)
76.9 ± 7.3
76.9 (64.5 - 88.0)
Data are mean ± SD (top row); median and (range) provided in bottom row
*Coconut water from concentrate greater than bottled water (p = 0.023); when expressed as change from Pre Dehydrating Exercise at 3 hours Post Dehydrating
Exercise. No other differences noted (p > 0.05).
Table 4 Fluid retention of exercise-trained men before and after dehydrating exercise
Time VitaCoco
®
Sport Drink Coconut Water
From Concentrate
Bottled Water
1 hour Post
Dehydrating Exercise
73.6 ± 22.1
76.0 (30.9 - 101.5
76.4 ± 21.1
77.9 (37.6 - 101.5)
83.5 ± 9.7
84.0 (67.2 - 101.5)
82.1 ± 22.3
88.0 (42.8 - 115.9)
2 hours Post
Dehydrating Exercise
59.6 ± 31.7
71.4 (-3.8 - 99.0)
60.6 ± 19.5
66.8 (28.4 - 90.9)
67.6 ± 13.7
63.0 (37.8 - 85.5)
56.9 ± 26.6
62.1 (0.0 - 95.7)
3 hours Post
Dehydrating Exercise*
39.0 ± 37.9
35.7 (-42.2 - 99.0)
40.3 ± 24.9
38.9 (-5.7 - 74.8)
51.7 ± 14.9
46.2 (29.4 - 75.6)
34.7 ± 23.9
32.9 (-10.7 - 65.5)
Data are mean ± SD (top row); median and (range) provided in bottom row
*Coconut water from concentrate greater than bottled water (p = 0.041) at 3 hours Post Dehydrating Exercise. No other differences noted (p > 0.05).
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 6 of 10
Discussion
Findings from the present investigatio n indicate that all
of the t ested beverages are capable of promoting rehy-
dration after one hour of dehydrating exercise. With few
exceptions at selected time points, findings for all rehy-
dration variables were essentially the same when com-
paring the carbohydrate- electrolyte sport drink, coconut
water (concentrated and not from concentrate), and
bottled water. Moreover, no differences were noted in
treadmill per formance durin g the r ehydration period.
These data are specific to a sample of young, exercise-
trained, healthy men.
Maintaining hydration status is vital for athletes and
can directly impact exercise performance [25]. As such,
many stud ies have been cond ucted t o determine the
optimal rehydration strategies. While water intake is
likely an adequate rehydration approach f or many indi-
viduals, others (e.g., athletes involved in vigorous train-
ing) may require intake of water-carbohydrate or
carbohydrate-electrolyte mi xtures [2], in addition to
other nutrients [26]. Such an approach has been
reported to be superior to water alone and is generally
considered the ideal recomme ndation for individuals
engaged in long duration, strenuous bouts of acute exer-
cise [2,4].
Related to the above, the use of coconut water has
been considered by many, as this beverage provides a
natural source of carbohydrate and electro lytes [9]. Spe-
cifically, coconut water has been reported to provide
sugar ( ~1 g ∙ dL
-1
), potassium (~51 mEq ∙ L
-1
), sodium
(~33 mEq ∙ L
-1
), and chloride (~52 mEq ∙ L
-1
) [9]; how-
ever, this may vary depending on species of coconut
palm. Coconut water has been reported to provide
hydrating effects similar to those of carbohydrate-elec-
trolyte sport drinks [16-18].
Saat and c olleagues used a cross-over study to assess
the effectiveness of fresh young coconut water and a
carbohydrate-electrolyte beverage, compared to water on
measures of whole body rehydration and blood volume
restoration during a two hour rehydration period follow-
ing a bout of dehydrating exercise [16]. A sample of
eight young men participated and consumed the
assigned beverage at a volume equal to 120% of the
fluid loss during exercise. No sta tisti cally significant dif-
ferences were noted between conditions for any out-
come measure; however, blood volume restoration was
noted to be slightly greater for coconut water. This
same group reported similar findings in a follow-up
study published in 2007 [17], using the same volume of
beverages (120% of fluid loss during exercise). More
recently, Idárraga and Aragón-Vargas studied the rehy-
drating effect of coconut water following exercise [18].
On three d ifferent days, six men and five women w ere
dehydrated t o approximately 2% body mass by exercis-
ing in a climate-controlled laboratory. On each day and
in random order, subjects were rehydrated with fresh
coconut w ater, a sport drink, or plain water using a
volume equal to 120% of body weight lost during e xer-
cise. Subjects were then monitored for three hours, with
urine collection every 30 minutes. No differences were
Table 5 Plasma osmolality of exercise-trained men before and after dehydrating exercise
Time VitaCoco
®
Sport Drink Coconut Water
From Concentrate
Bottled Water
Pre Dehydrating Exercise 289.3 ± 4.5
288.5 (282.0 - 300.0)
291.5 ± 6.0
290.0 (283.0 - 305.0)
293.0 ± 5.6
291.0 (287.0 - 305.0)
292.0 ± 5.0
291.0 (282.0 - 300.0)
Immediately Post
Dehydrating Exercise
297.5 ± 5.6
297.5 (290.0 - 309.0)
297.7 ± 8.0
297.0 (289.0 - 320.0)
297.5 ± 6.1
296.0 (289.0 - 309.0)
297.6 ± 4.5
297.5 (290.0 - 305.0)
3 hours Post
Dehydrating Exercise*
291.2 ± 6.6
290.0 (285.0 - 310.0)
289.6 ± 5.5
288.0 (283.0 - 304.0)
291.8 ± 5.7
289.0 (286.0 - 306.0)
290.3 ± 5.1
289.5 (284.0 - 302.0)
Data are mean ± SD (top row); median and (range) provided in bottom row
*Coconut water from concentrate greater than bottled water (p = 0.049); when expressed as change from Pre Dehydrating Exercise at 3 hours Post Dehydrating
Exercise. No other differences noted (p > 0.05).
Table 6 Urine specific gravity of exercise-trained men before and after dehydrating exercise
Time VitaCoco
®
Sport Drink Coconut Water
From Concentrate
Bottled Water
Pre Dehydrating Exercise 1.0204 ± 0.0087
1.02 (1.01 - 1.03)
1.0218 ± 0.0096
1.03 (1.00 - 1.032)
1.0217 ± 0.0106
1.03 (1.01 - 1.03)
1.0231 ± 0.0068
1.03 (1.01 - 1.03)
Immediately Post
Dehydrating Exercise
1.0158 ± 0.0102
1.02 (1.01 - 1.03)
1.0165 ± 0.0112
1.018 (1.00 - 1.03)
1.0153 ± 0.0098
1.02 (1.00 - 1.03)
1.0161 ± 0.0077
1.02 (1.00 - 1.03)
3 hours Post
Dehydrating Exercise
1.0200 ± 0.0098
1.03 (1.01 - 1.03)
1.0060 ± 0.0037
1.01 (1.00 - 1.02)
1.0139 ± 0.0066
1.02 (1.00 - 1.03)
1.0055 ± 0.0022
1.01 (1.00 - 1.01)
Data are mean ± SD (top row); median and (range) provided in bottom row
No differences noted (p > 0.05).
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 7 of 10
noted between coconut water and sport drink for urine
volume or fluid retention (both were better than plain
water).
These above s tudies focused exclusively on hydration
measures, following a period of dehydrating exercise
and consumption of the assigned beverage, while not
emphasizing exercise performance during the rehydrat-
ing period. The present study, using a similar fluid
volume as used previously, extends these findings by
noting similar exercise performance re sults for natural
coc onut wa ter (concentrated and not fr om concentra te)
and a carbohydrate-electrolyte sport drink. For most
athletes and coaches, this finding is likely of most
importance. Our data indicate that coconut water can
provide similar benefits as compared to a typical sport
drink in terms of exercise performance (as measured
based on tre admill time to exhaus tion), in ad dition to
measures of hydration. That being said, one potential
concern is subject tolerance to coconut water in such
high volumes. Subjects reported feeling somewhat
bloated and experienced mild stomach upset with the
two forms of coconut water used in the present investi-
gation (Table 7), which is likely due to the high volume
of fluid re quired to be consumed in su ch a short period
of time. As with most bever ages, individual tolerance to
coconut water should be determined prior to use.
It should be noted that this study explored many end -
points at many time-points, each being compared
between four products. Consequently, many hundreds of
separate pairw ise com parisons were ca rried out, each
generating a p value, raising the issue of multiplicity and
inflated Type-1 error. No multiple-test adjustments
(Bonferroni or other) were applied - it would have been
unrealistic and unproductive to try to establish a study-
Table 7 Subjective ratings of exercise-trained men before and after dehydrating exercise
Time VitaCoco
®
Sport Drink Coconut Water
From Concentrate
Bottled Water
Thirst
Immediately Post DHE 4.08 ± 1.16 4.42 ± 0.67 4.45 ± 0.69 4.67 ± 0.65
1 hour Post DHE 1.17 ± 0.58 1.33 ± 0.89 1.36 ± 0.67 1.08 ± 0.29
2 hours Post DHE 1.50 ± 0.52 1.58 ± 0.67 1.45 ± 0.52 1.50 ± 0.67
3 hours Post DHE 1.67 ± 0.65 1.83 ± 0.94 1.45 ± 0.82 1.92 ± 1.00
Bloatedness
Immediately Post DHE 1.33 ± 0.49 1.33 ± 0.65 1.55 ± 1.04 1.33 ± 0.49
1 hour Post DHE 3.58 ± 1.00 3.42 ± 1.24 4.00 ± 1.34 3.08 ± 1.24
2 hours Post DHE 2.75 ± 0.97 1.67 ± 0.65 2.82 ± 1.17 1.50 ± 0.67
3 hours Post DHE 2.33 ± 1.23 1.42 ± 0.67 2.45 ± 1.21 1.25 ± 0.62
Refreshed
Immediately Post DHE 1.92 ± 1.00 2.08 ± 1.24 2.09 ± 1.22 1.67 ± 0.89
1 hour Post DHE 3.25 ± 1.36 3.83 ± 1.27 3.82 ± 1.08 4.17 ± 1.19
2 hours Post DHE 3.33 ± 1.23 3.67 ± 1.23 3.64 ± 1.50 3.58 ± 1.16
3 hours Post DHE 3.17 ± 1.19 3.33 ± 1.15 3.55 ± 1.51 3.50 ± 1.09
Stomach Upset
Immediately Post DHE 1.58 ± 0.79 1.25 ± 0.45 1.00 ± 0.00 1.00 ± 0.00
1 hour Post DHE 2.75 ± 1.29 2.00 ± 1.35 3.18 ± 1.66 1.67 ± 0.89
2 hours Post DHE 3.33 ± 1.23 1.25 ± 0.62 3.09 ± 1.51 1.25 ± 0.45
3 hours Post DHE 2.92 ± 1.31 1.17 ± 0.39 2.55 ± 1.44 1.08 ± 0.29
Tiredness
Immediately Post DHE 3.58 ± 1.00 3.92 ± 0.79 3.82 ± 0.98 4.08 ± 0.79
1 hour Post DHE 2.83 ± 0.83 3.08 ± 0.90 2.64 ± 0.92 2.92 ± 1.00
2 hours Post DHE 2.08 ± 0.90 2.58 ± 0.90 2.36 ± 0.81 2.33 ± 0.98
3 hours Post DHE 2.08 ± 0.90 2.50 ± 1.00 2.18 ± 0.98 2.33 ± 0.78
Data are mean ± SD
Thirst: No differences between conditions (p > 0.05).
Bloatedness: 3 hours Post DHE > Immediately Post DHE for VitaCoco
®
(p = 0.012) and coconut water from concentrate (p = 0.034)
Refreshed: 1 hour Post DHE > Immediately Post DHE for bottled water compared to VitaCoco
®
(p = 0.036).
Stomach Upset: Greater stomach upset at 3 hours Post DHE for VitaCoco
®
compared to sport drink (p = 0.034), VitaCoco
®
compared to bottled water (p = 0.046),
coconut water from concentrate compared to sport drink (p = 0.020) and coconut water from concentrate compared to bottled water (p = 0.020).
Tiredness: No differences between conditions (p > 0.05).
DHE = Dehydrating Exercise
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 8 of 10
wide 0.05 alpha level, which would have required impos-
sibly small p-values on individual tests. So it should be
kept in mind that each individual p value has a one-in-
twenty chance of bein g nominally significant (p < 0.05)
purely from random fluctuations. Conclusions of relative
efficacy among the different products s hould not be
basedsimplyonisolatedpvalues,butratheronacon-
siderat ion of the complete set of data for each endpoint.
Likewise, observed v alues were not simply put into a
repeated-measures ANOVA to test for overall changes
over time - most endpoints displayed very significant
changes at certain ti me points (such as f rom baseline to
immediately post-dehydrating exercise). It was much
more appropriate to examination the changes (and dif-
ferences in mean changes between products) only over
certain physiologically-meaningful intervals, and indivi-
dual t-tests were much more directly interpretable, and
therefore more useful, in assessing these specific
changes.
Conclusion
Considering the above, our data indicate that both
coconut water (natural, concentrated and not from
concentrate) and bottled water provide similar rehy-
drating effects as compared to a carbohydrate-electro-
lyte sport drink. Moreover, none of the beverages
impacted treadmill exercise performance differently
during the rehydration period. Additional study is
needed wi th consi deration for th e inclusio n of a more
demanding dehydration protocol, aimed at reducing
body mass beyond the 2% mark obtained in the
present investigation may be warranted. Finally, while
treadmill time to exhaustion is routinely used in
laboratory studies, the use ofatimetrialtestasthe
measureofexerciseperformancemaybemoreappro-
priate. Investigators may consider these su ggestions
when designing f uture studies focused on the potential
rehydrating ability of coconut water and other
beverages.
Acknowledgements
Funding for this work was provided by VitaCoco® Company (New York, NY).
Author details
1
Miami Research Associates, Nutrition/Endocrinology Department, 6141
Sunset Drive, Suite 301, Miami, FL 33143.
2
The University of Memphis,
Cardiorespiratory/Metabolic Laboratory, Department of Health and Sport
Sciences, 106 Roane Fieldhouse, Memphis, TN 38152.
Authors’ contributions
DSK, SF, and DRK were responsible for the study design, coordination of the
study, and oversight of data collection and analysis. RJB assisted in
manuscript preparation. All authors read and approved of the final
manuscript.
Competing interests
Financial support for this work was provided by VitaCoco® Company (New
York, NY). The investigators have no direct or indirect interest in VitaCoco®.
RJB has received research funding or has acted as a consultant to
nutraceutical and dietary supplement companies.
Received: 15 December 2011 Accepted: 18 January 2012
Published: 18 January 2012
References
1. Rodriguez NR, DiMarco NM, Langley S, American Dietetic Association,
Dietetians of Canada, American College of Sports Medicine: Position of the
American Dietetic Association, Dietitians of Canada, and the American
Table 8 Heart rate and blood pressure of exercise-trained men before and after dehydrating exercise
Time VitaCoco
®
Sport Drink Coconut Water
From Concentrate
Bottled Water
Heart Rate
Pre DHE 63.6 ± 8.7 63.3 ± 6.7 64.6 ± 11.6 62.7 ± 6.5
Immediately Post DHE 102.1 ± 19.9 101.8 ± 12.8 103.4 ± 13.0 102.0 ± 18.1
Pre PE 70.2 ± 11.2 71.2 ± 9.8 68.5 ± 9.1 64.2 ± 7.6
Immediately Post PE 86.8 ± 15.0 88.0 ± 17.5 96.1 ± 35.7 84.6 ± 15.2
Systolic Blood Pressure
Pre DHE 122.8 ± 9.6 119.6 ± 9.5 121.0 ± 9.4 122.3 ± 8.4
Immediately Post DHE 109.2 ± 9.6 116.8 ± 12.1 113.6 ± 11.7 112.7 ± 4.3
Pre PE 122.1 ± 9.4 116.7 ± 8.4 120.9 ± 9.3 117.6 ± 8.7
Immediately Post PE 120.8 ± 11.9 121.6 ± 9.6 117.7 ± 9.9 115.7 ± 10.3
Diastolic Blood Pressure
Pre DHE 77.8 ± 5.2 75.0 ± 7.5 78.3 ± 7.3 76.7 ± 3.9
Immediately Post DHE 66.8 ± 7.1 73.1 ± 7.0 71.1 ± 7.3 72.2 ± 5.9
Pre PE 76.3 ± 4.3 74.1 ± 5.6 74.8 ± 5.8 73.5 ± 5.2
Immediately Post PE 77.6 ± 6.6 76.6 ± 6.4 74.5 ± 6.6 74.3 ± 7.5
Data are mean ± SD
No differences noted (p > 0.05).
DHE = Dehydrating Exercise
PE = Performance Exercise
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 9 of 10
College of Sports Medicine: Nutrition and athletic performance. JAm
Diet Assoc 2009, 109(3):509-27.
2. von Duvillard SP, Arciero PJ, Tietjen-Smith T, Alford K: Sports drinks,
exercise training, and competition. Curr Sports Med Rep 2008, 7(4):202-8.
3. American College of Sports Medicine, Sawka MN, Burke LM, Eichner ER,
Maughan RJ, Montain SJ, Stachenfeld NS: American College of Sports
Medicine position stand. Exercise and fluid replacement. Med Sci Sports
Exerc 2007, 39(2):377-90.
4. Von Duvillard SP, Braun WA, Markofski M, Beneke R, Leithäuser R: Fluids
and hydration in prolonged endurance performance. Nutrition 2004,
20(7-8):651-6.
5. Convertino VA, Armstrong LE, Coyle EF, Mack GW, Sawka MN, Senay LC Jr,
Sherman WM: American College of Sports Medicine position stand.
Exercise and fluid replacement. Med Sci Sports Exerc 1996, 28(1):i-vii.
6. Rehrer NJ: Fluid and electrolyte balance in ultra-endurance sport. Sports
Med 2001, 31(10):701-15.
7. Kreider RB, Wilborn CD, Taylor L, Campbell B, Almada AL, Collins R,
Cooke M, Earnest CP, Greenwood M, Kalman DS, Kerksick CM, Kleiner SM,
Leutholtz B, Lopez H, Lowery LM, Mendel R, Smith A, Spano M, Wildman R,
Willoughby DS, Ziegenfuss TN, Antonio J: ISSN exercise & sport nutrition
review: research & recommendations. J Int Soc Sports Nutr 2010, 7:7.
8. , http://researchwikis.com/Sports_Drink_Market: Accessed 10/18/11.
9. Chavalittamrong B, Pidatcha P, Thavisri U: Electrolytes, sugar, calories,
osmolarity and pH of beverages and coconut water. Southeast Asian J
Trop Med Public Health 1982, 13(3):427-31.
10. Kuberski T, Roberts A, Linehan B, Bryden RN, Teburae M: Coconut water as
a rehydration fluid. N Z Med J 1979, 90(641):98-100.
11. Chavalittamrong B, Pidatcha P, Thavisri U: Electrolytes, sugar, calories,
osmolarity and pH of beverages and coconut water. Southeast Asian J
Trop Med Public Health 1982, 13(3):427-31.
12. Adams W, Bratt DE: Young coconut water for home rehydration in
children with mild gastroenteritis. Trop Geogr Med 1992, 44(1-2):149-53.
13. Campbell-Falck D, Thomas T, Falck TM, Tutuo N, Clem K: The intravenous
use of coconut water. Am J Emerg Med 2000, 18(1):108-11.
14. Mantena SK, Jagadish , Badduri SR, Siripurapu KB, Unnikrishnan MK: In vitro
evaluation of antioxidant properties of Cocos nucifera Linn. water.
Nahrung 2003, 47(2):126-31.
15. Fisher-Wellman K, Bloomer RJ: Acute exercise and oxidative stress: a 30
year history. Dyn Med 2009,
8:1.
16. Saat M, Singh R, Sirisinghe RG, Nawawi M: Rehydration after exercise with
fresh young coconut water, carbohydrate-electrolyte beverage and plain
water. J Physiol Anthropol Appl Human Sci 2002, 21(2):93-104.
17. Ismail I, Singh R, Sirisinghe RG: Rehydration with sodium-enriched
coconut water after exercise-induced dehydration. Southeast Asian J Trop
Med Public Health 2007, 38(4):769-85.
18. Idárraga AP, Aragón-Vargas LF: Post-exercise rehydration with coconut
water [abstract]. Med Sci Sports Exerc 2010, 42(5):575.
19. Moran DS, Heled Margaliot M, Shani Y, Laor A, Margaliot S, Bickes E,
Shapiro Y: Hydration status measurement by radio frequency
absorptiometry in young athletes - a new method and preliminary
results. Physiol Meas 2004, 25:51-59.
20. Antonio J, Sanders MS, Ehler LA, Uelmen J, Raether JB, Stout JR: Effects of
exercise training and amino acid supplementation on body composition
and physical performance in untrained women. Nutrition 2000,
16:1043-1046.
21. Cheuvront SN, Ely BR, Kenefick RW, Sawka MN: Biological variation and
diagnostic accuracy of dehydration assessment markers. Am J Clin Nutr
2010, 92(3):565-73.
22. Wong SH, Chen Y: Effect of a carbohydrate-electrolyte beverage, lemon
tea, or water on rehydration during short-term recovery from exercise.
Int J Sport Nutr Exerc Metab 2011, 21(4):300-10.
23. Armstrong LE, Maresh CM, Castellani JW, Bergeron MF, Kenefick RW,
LaGasse KE, Riebe D: Urinary indices of hydration status. Int J Sport Nutr
1994, 4(3):265-79.
24. Popowski LA, Oppliger RA, Patrick Lambert G, Johnson RF, Kim Johnson A,
Gisolf CV: Blood and urinary measures of hydration status during
progressive acute dehydration. Med Sci Sports Exerc 2001, 33(5):747-53.
25. Lopez RM, Casa DJ, Jensen KA, Demartini JK, Pagnotta KD, Ruiz RC,
Roti MW, Stearns RL, Armstrong LE, Maresh CM: Examining the influence
of hydration status on physiological responses and running speed
during trail running in the heat with controlled exercise intensity. J
Strength Cond Res 2011, 25(11):2944-54.
26. Spaccarotella KJ, Andzel WD: Building a beverage for recovery from
endurance activity: a review. J Strength Cond Res 2011, 25(11):3198-204.
doi:10.1186/1550-2783-9-1
Cite this article as: Kalman et al.: Comparison of coconut water and a
carbohydrate-electrolyte sport drink on measures of hydration and
physical performance in exercise-trained men. Journal of the International
Society of Sports Nutrition 2012 9:1.
Submit your next manuscript to BioMed Central
and take full advantage of:
• Convenient online submission
• Thorough peer review
• No space constraints or color figure charges
• Immediate publication on acceptance
• Inclusion in PubMed, CAS, Scopus and Google Scholar
• Research which is freely available for redistribution
Submit your manuscript at
www.biomedcentral.com/submit
Kalman et al. Journal of the International Society of Sports Nutrition 2012, 9:1
http://www.jissn.com/content/9/1/1
Page 10 of 10
