Comparing the rehydration potential of different milk-based drinks to a carbohydrate–electrolyte beverage

Abstract

The aim of this study was to compare the rehydration potential of a carbohydrate–electrolyte beverage with several varieties of milk following exercise-induced fluid losses. Fifteen male participants (age 24.9 ± 5.5 years, height 179.3 ± 4.9 cm, body mass 75.8 ± 6.6 kg (mean ± SD)) lost 2.0% ± 0.2% body mass through intermittent cycling before consuming a different beverage on 4 separate occasions. Drinks included cow’s milk (286 kJ·100 mL⁻¹), soy milk (273 kJ·100 mL⁻¹), a milk-based liquid meal supplement (Sustagen Sport (Nestle); 417 kJ·100 mL⁻¹), and a sports drink (Powerade (Coca Cola Ltd); 129 kJ·100 mL⁻¹). Beverages were consumed over 1 h in volumes equivalent to 150% of body mass loss. Body mass, blood and urine samples, and measures of gastrointestinal tolerance were obtained before and hourly for 4 h after beverage consumption. Net body mass at the conclusion of each trial was significantly less with Powerade (–1.37 ± 0.3 kg) than with cow’s milk (–0.92 ± 0.48 kg), soy milk (–0.78 ± 0.37 kg), and Sustagen Sport (–0.48 ± 0.39 kg). Net body mass was also significantly greater for Sustagen Sport compared with cow’s milk trials, but not soy milk. Upon completion of trials, the percentage of beverage retained was Sustagen Sport 65.1% ± 14.7%, soy milk 46.9% ± 19.9%, cow’s milk 40.0% ± 24.9%, and Powerade 16.6% ± 16.5%. Changes in plasma volume and electrolytes were unaffected by drink treatment. Subjective ratings of bloating and fullness were higher during all milk trials compared with Powerade whereas ratings of overall thirst were not different between beverages. Milk-based drinks are more effective rehydration options compared with traditional sports drinks. The additional energy, protein, and sodium in a milk-based liquid meal supplement facilitate superior fluid recovery following exercise.

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ARTICLE
Comparing the rehydration potential of different milk-based
drinks to a carbohydrate–electrolyte beverage
Ben Desbrow, Sarah Jansen, Abby Barrett, Michael D. Leveritt, and Christopher Irwin
Abstract: The aim of this study was to compare the rehydration potential of a carbohydrate–electrolyte beverage with several
varieties of milk following exercise-induced fluid losses. Fifteen male participants (age 24.9 ± 5.5 years, height 179.3 ± 4.9 cm,
body mass 75.8 ± 6.6 kg (mean ± SD)) lost 2.0% ± 0.2% body mass through intermittent cycling before consuming a different
beverage on 4 separate occasions. Drinks included cow’s milk (286 kJ·100 mL
−1
), soy milk (273 kJ·100 mL
−1
), a milk-based liquid
meal supplement (Sustagen Sport (Nestle); 417 kJ·100 mL
−1
), and a sports drink (Powerade (Coca Cola Ltd); 129 kJ·100 mL
−1
).
Beverages were consumed over1hinvolumes equivalent to 150% of body mass loss. Body mass, blood and urine samples, and
measures of gastrointestinal tolerance were obtained before and hourly for 4 h after beverage consumption. Net body mass at the
conclusion of each trial was significantly less with Powerade (–1.37 ± 0.3 kg) than with cow’s milk (–0.92 ± 0.48 kg), soy milk
(–0.78 ± 0.37 kg), and Sustagen Sport (–0.48 ± 0.39 kg). Net body mass was also significantly greater for Sustagen Sport compared
with cow’s milk trials, but not soy milk. Upon completion of trials, the percentage of beverage retained was Sustagen Sport
65.1% ± 14.7%, soy milk 46.9% ± 19.9%, cow’s milk 40.0% ± 24.9%, and Powerade 16.6% ± 16.5%. Changes in plasma volume and
electrolytes were unaffected by drink treatment. Subjective ratings of bloating and fullness were higher during all milk trials
compared with Powerade whereas ratings of overall thirst were not different between beverages. Milk-based drinks are more
effective rehydration options compared with traditional sports drinks. The additional energy, protein, and sodium in a milk-
based liquid meal supplement facilitate superior fluid recovery following exercise.
Key words: hydration, diet, sports nutrition, exercise.
Résumé : Cette étude se propose de comparer le potentiel de réhydratation d’une boisson contenant des sucres et des électro-
lytes a
`quelques variétés de boissons lactées a
`la suite de la perte de liquides corporels suscitée par l’exercice physique. Quinze
hommes (moyenne ± écart-type : 24,9 ± 5,5 ans, 179,3 ± 4,9 cm, 75,8 ± 6,6 kg) perdent 2,0 ± 0,2 % de leur masse corporelle en
pédalant par intermittence préalablement a
`la consommation de boissons différentes en quatre occasions distinctes. Les liquides
consommées sont : lait de vache (286 kJ·100 mL
−1
), lait de soja (273 kJ·100 mL
−1
), supplément de repas liquide a
`base de lait
(Sustagen Sport; 417 kJ·100 mL
−1
) et boisson pour sportif (Powerade; 129 kJ·100 mL
–1
). Les sujets consomment en 1 h des quantités
équivalant a
`150 % de la masse corporelle perdue. On évalue la masse corporelle, des échantillons de sang et d’urine et la tolérance
gastro-intestinale avant et aux heures pendant quatre heures après la consommation de la boisson. À la fin de chaque essai, la
masse corporelle nette est significativement inférieure dans la condition Powerade (–1,37 ± 0,3 kg) comparativement aux autres
conditions : lait de vache (–0,92 ± 0,48 kg), lait de soja (–0,78 ± 0,37 kg) et Sustagen Sport (–0,48 ± 0,39 kg). La masse corporelle
est aussi significativement supérieure dans la condition Sustagen Sport comparativement a
`la condition lait de vache, mais pas
par rapport a
`la condition lait de soja. À la fin de chacun des essais, le pourcentage de boisson retenue est : Sustagen Sport 65,1 ±
14,7 %, lait de soja 46,9 ± 19,9 %, lait de vache 40,0 ± 24,9 % et Powerade 16,6 ± 16,5 %. La variation du volume plasmatique et de
la concentration des électrolytes n’est pas affectée par le genre de boisson. Les sensations de ballonnement et de satiété sont plus
marquées dans toutes les conditions comprenant du lait comparativement a
`la condition Powerade; les sensations de soif ne
diffèrent pas d’une condition a
`l’autre. Les boissons a
`base de lait sont plus efficaces sur le plan de la réhydratation compara-
tivement aux boissons traditionnelles pour sportifs. L’énergie, les protéines et le sodium en plus contenus dans les suppléments
liquides a
`base de lait procurent une plus grande récupération des fluides après un exercice. [Traduit par le Rédaction]
Mots-clés : hydratation, diète, nutrition sportive, exercice physique.
Introduction
During exercise, sweat output often exceeds fluid intake, pro-
ducing a fluid deficit or hypohydration. Before recommencing
exercise, the hypohydrated athlete is encouraged to consume bev-
erages to restore all fluids and electrolytes that were lost (Sawka
et al. 2007). This is because hypohydration impairs performance
in both high-intensity exercise (Armstrong et al. 1985;Moquin and
Mazzeo 2001;Walsh et al. 1994) and endurance exercise (Ebert
et al. 2007), as well as applied motor skills (Devlin et al. 2001) and
some cognitive performance measures (Tomporowski et al. 2007),
particularly when the level of hypohydration exceeds 2% of body
mass. Consequently, it is important to investigate factors that
Received 13 May 2014. Accepted 8 July 2014.
B. Desbrow. School of Allied Health Sciences, Griffith University, Gold Coast, Australia; Research Centre for Health Practice Innovation, Griffith Health
Institute, Griffith University, Gold Coast, Australia.
S. Jansen and A. Barrett. School of Allied Health Sciences, Griffith University, Gold Coast, Australia.
M.D. Leveritt. School of Allied Health Sciences, Griffith University, Gold Coast, Australia; School of Human Movement Studies, University of
Queensland, Brisbane, Australia.
C. Irwin. Research Centre for Health Practice Innovation, Griffith Health Institute, Griffith University, Gold Coast, Australia.
Corresponding Author: Ben Desbrow (e-mail: b.desbrow@griffith.edu.au).
1366
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may enhance a beverage’s ability to quickly restore fluid and elec-
trolyte balance after exercise.
Consumption of dilute fluids, such as plain water, after exercise
leads to a decline in plasma osmolality and sodium concentration,
resulting in increased rates of fluid excretion, potentially compro-
mising rehydration (Shirreffs et al. 2007a). However, certain nu-
trients have been demonstrated to improve a beverage’s ability to
restore fluid balance after exercise. First, the addition of sodium
to a postexercise beverage will cause greater fluid retention
(Merson et al. 2008;Nose et al. 1988;Shirreffs et al. 1996). The
addition of carbohydrate to a rehydration beverage can also cause
modest increases in fluid retention following exercise (Evans et al.
2009;Osterberg et al. 2010). Finally, protein has been shown to aid
in fluid retention when added to postexercise rehydration bever-
ages (James et al. 2011;Seifert et al. 2006).
Milk is a popular beverage that contains sodium, carbohydrate,
and protein. Indeed, cow’s milk has been demonstrated to be
more effective for postexercise rehydration when compared with
traditional sports drinks (Shirreffs et al. 2007b;Watson et al.
2008). Cow’s milk consumption after exercise results in 40%–50%
less urine output than the same volume of a sports drink or water
(Shirreffs et al. 2007b;Watson et al. 2008). Milk could therefore be
an effective alternative for those attempting to rehydrate rapidly
after exercise.
The effectiveness of milk as a rehydration solution can be re-
lated to a number of its constituents. Cow’s milk is naturally high
in sodium; however, the addition of sodium to milk provides no
further benefit to fluid restoration following exercise (Shirreffs et al.
2007b). Adding 25 g of milk protein to a traditional carbohydrate–
electrolyte solution enhances fluid retention after exercise com-
pared with an isocaloric beverage devoid of protein (James et al.
2011). In contrast, a similar study that investigated the effect of 15-g
whey protein isolate failed to demonstrate similar improvement of
postexercise rehydration (James et al. 2012). When individual constit-
uents of milk beverages are investigated in isolation, the effective-
ness on rehydration appears less convincing (Ishihara et al. 2013).
This suggests that greater emphasis should be placed on investigat-
ing the rehydration potential of milk, as it is typically consumed.
While cow’s milk is widely available, relatively inexpensive,
and well-liked, it cannot be consumed by all individuals. For in-
stance, it is well known that lactase production persists into adult
life in some people but not in others (Ingram et al. 2009). Further-
more, alternative fortified milk-based products (liquid meal
supplements) are often promoted to athletes to enhance muscle
refuelling and promote muscle protein synthesis while providing
a convenient portable option that does not require refrigeration.
The rehydration potential of these milk alternatives in compari-
son with cow’s milk and carbohydrate–electrolyte beverages re-
mains unknown. Therefore, the aim of this study was to compare
the rehydration effectiveness of 4 beverages Oa carbohydrate–
electrolyte drink, cow’s milk, an energy-, protein-, and sodium-
matched soy milk, and a commercially available milk-based liquid
meal supplement Ofollowing exercise-induced fluid loss.
Materials and methods
Experimental design
This study involved a cross-over design with each participant com-
pleting 4 different experimental trials. The order of treatment was
randomized using an incomplete Latin-square design, and each
trial was separated by at least 7 days. The 4 beverages investigated
were cow’s milk, soy milk, a high-protein milk-based formulated
supplementary sports food (Sustagen Sport; Nestle), and a carbohy-
drate–electrolyte sports drink (Powerade; Coca Cola Ltd). Each ex-
perimental trial involved participants exercising until body
mass was reduced by approximately 2%. After the exercise pe-
riod, participants consumed a total volume of beverage equal to
150% of fluid lost. The total volume of beverage was required to be
consumed in a 1-h period. Body mass and blood and urine samples
and measures of gastrointestinal tolerance were then collected
during a 4-h period in which participants rested in the laboratory.
Participants
Twenty healthy and recreationally active males, who all re-
ported tolerance to lactose, volunteered to participate in this
study. The number of participants was selected following a sam-
ple size calculation (G*Power version 3.0). The results of Shirreffs
et al. (2007) indicated the difference in net fluid balance between
a carbohydrate–electrolyte beverage and milk was large (effect
size of 2.6). To be conservative, we anticipated an effect size of 1.0
and with a power of 80% and ␣= 0.05; the calculation suggested
that a sample size of 9 participants was required. Fifteen subjects
were recruited to accommodate some attrition because of the
experimental burden. The investigation received approval from
the Griffith University Human Research Ethics Committee and
conformed to its policy statement regarding the use of human
subjects and written informed consent.
Beverage treatments
Participants consumed 1 of 4 beverage solutions in each of the
4 experimental trials. The beverages were (i) a commercially
available carbohydrate–electrolyte sports drink (Powerade), (ii) soy
milk (So Good Regular, Sanitarium), (iii) cow’s milk (Pauls Full
Cream, Parmalat), or (iv) a high-carbohydrate, high-protein liquid-
meal supplement (Sustagen Sport). The particular brands of soy
and cow’s milk beverages were chosen as they have similar
amounts of energy, protein, fat, carbohydrate, and sodium per
serving. The energy, macronutrient, and sodium composition of
each beverage is outlined in Table 1.
Procedures
Participants arrived at the laboratory in the morning following
an overnight fast. Participants were asked to abstain from alcohol
consumption for 24 h and caffeine-containing products (including
foods and beverages) for 12 h prior to each trial. In addition, par-
ticipants were required to refrain from moderate to strenuous
activity 12 h prior to the trials and were encouraged to keep food
intake as consistent as possible in the 24 h prior to each trial.
Compliance with these pre-trial standardization procedures was
confirmed verbally on arrival to the laboratory.
Prior to commencing exercise a urine sample was collected
from each participant, urine specific gravity (USG; Palette Digital
Refractometer, ATAGO, USA) was measured to determine hydra-
tion status. Participants that were not adequately hydrated on
arrival to the laboratory (USG > 1.020) were required to consume a
bolus of water and rest in the laboratory until a further urine
sample could be produced indicating a USG recording below the
Table 1. Trial beverage nutrient profiles.
Beverage
Energy
(kJ·100 mL
−1
)
Protein
(g·100 mL
−1
)
Fat
(g·100 mL
−1
)
CHO
(g·100 mL
−1
)
Na
+
(mg·100 mL
−1
)
Cow’s milk (Paul’s) 286 3.6 3.8 4.9 41
Soy milk (Sanitarium So Good) 273 3.2 3.5 5.1 45
LiquiLiquid meal supplement (Sustagen Sport) 417 6.5 0.2 17.6 67
CHO−electrolyte drink (Powerade) 129 0 0 7.3 28
Note: CHO, carbohydrate.
Desbrow et al. 1367
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threshold for euhydration. Only 3 participants required addi-
tional water and on each occasion they consumed 300 mL.
Initial nude body mass was measured and participants began
exercising on a cycle ergometer (Monark Ergomedic 828E, GIH,
Sweden) at 70%–80% of their age-predicted maximum heart rate
until ⬃1.8% of their initial body mass was lost. Participants exer-
cised in heavy clothing to encourage sweat loss. Subsequent nude
body mass was measured at regular intervals until the required
body mass was lost, at which point the subject stopped cycling to
allow the remainder of mass loss to occur throughout the cool
down. If ⬃1.8% body mass deficit was not achieved subjects were
instructed to continue exercising until this goal was reached. A
rest period of 30 min occurred after the exercise phase to allow
subjects to have a cool shower, return to the laboratory, and rest.
A final nude body mass was then taken to determine the volume
of fluid required for consumption. Trials were conducted at the
same time of day in a stable laboratory environment (22±2°C,
60%–70% relative humidity).
Over the next 60 min, the subjects ingested one of the rehydra-
tion beverages. The entire beverage volume, equal to 150% of the
change in body mass, was divided into 4 equal parts, each of which
was consumed over a 15-min period. All beverages aliquots were
served cold (⬃4 °C), immediately from the refrigerator. For the
subsequent 4-h observation period, subjects remained within the
laboratory and were seated except for essential movements.
Fluid balance and retention
Total urine loss was calculated from the accumulated urine
output in the period from the commencement of drinking until
the end of the observation period (i.e., 5 h total). Participants were
permitted to urinate as required throughout the observation pe-
riod. Urine per hour was calculated following requested voiding at
the conclusion of each hour throughout this 5-h period. Net body
mass (a proxy for net fluid balance) was calculated by subtracting
the body mass (post voiding) from the initial body mass with fecal
losses being excluded via immediate pre–post body mass mea-
surements. When used across an acute time period, it is proposed
that body mass changes take into account urinary losses, sweat
loss, and other insensible losses and arrive at the value of com-
plete hydration status (Armstrong 2005). Finally, a value for fluid
retention was calculated by the following equation:
fluid retention ⫽[(volume of beverage consumed
⫺urine output after 4 h)/volume of beverage consumed] × 100
Blood measures
Prior to each blood sample, participants were asked to rest in a
supine position for at least 15 min to minimize the effects of
postural changes on the redistribution of water between the ma-
jor bodily compartments (Lambert et al. 1992). Once rested, a 2-mL
blood sample was drawn from an antecubital vein. Blood samples
were collected prior to exercise, following exercise, at the conclu-
sion of drinking, 1 h into the observation period, and at the end of
the observation period (4 h). Samples were stored in lithium hep-
arin vacutainers before being processed through an iSTAT blood
analyzer (i-STAT 1 Analyzer, Abbott, USA) for the measurement of
sodium, potassium, glucose, haemoglobin, and haematocrit con-
centrations. Plasma volume changes were calculated according to
the methods described by Dill and Costill (1974).
Subjective measures
Questionnaires were conducted during the rehydration phase
of the study to examine palatability of the different beverages and
gastrointestinal (GI) symptoms. The palatability questionnaire
was administered with the second and last of the 4 beverages
aliquots and consisted of ratings of overall pleasantness, saltiness,
sweetness, and bitterness. The GI questionnaire was conducted
prior to the first beverage (baseline), at 15 min following the sec-
ond and the last drink, and at hourly intervals until the end of the
observation period. Participants were asked to rate feelings of
thirst, fullness, hunger, energy, tiredness, alertness, and dryness
of mouth. All measures were conducted on a 100-mm visual ana-
logue scale (VAS), ranging from “not at all” to “a lot”, adminis-
tered using a laptop computer (Marsh-Richard et al. 2009).
Data analysis
All statistical procedures were performed using SPSS Statistics
for Windows, version 21.0 (IBM Corp. 2012, Armonk, N.Y., USA).
Statistical analysis for each of the main dependent variables
regarding hydration potential of beverages and VAS subjective re-
sponses were conducted using 2-way (beverage × time) repeated-
measures ANOVA. Post hoc analysis using Bonferroni correction
factor was performed on all significant Fratios. Statistical signif-
icance was accepted at p< 0.05. All data are reported as means ±
SD unless otherwise specified.
Results
Standardization procedures
Five recruited participants withdrew either immediately prior
to or following their first experimental trial. Two participants
withdrew because of competing time commitments, 1 failed to
respond following recruitment despite repeated contact attempts,
and 2 disliked the experimental protocol having completed their
first trial. Hence, 15 participants, (age, 24.9 ± 5.5 years; height,
179.3 ± 4.9 cm; body mass, 75.8 ± 6.6 kg) successfully completed all
4 experimental trials.
All participants arrived to the laboratory having stated compli-
ance with the pre-trial dietary and exercise control conditions.
According to USG threshold measurements, all participants com-
menced trials in a state of euhydration (cow’s milk = 1.012 ± 0.01,
soy milk = 1.010 ± 0.01, Sustagen Sport = 1.012 ± 0.01, Powerade =
1.015 ± 0.01) and participants commenced exercise with similar
starting body masses (cow’s milk = 75.8 ± 6.7 kg, soy milk = 75.5 ±
6.6 kg, Sustagen Sport = 75.7 ± 6.7 kg, Powerade = 76.1 ± 6.7 kg).
Exercise time was similar between trials (cow’s milk = 63.0 ±
6 min, soy milk = 61.3 ± 3 min, Sustagen Sport = 61.5 ± 13 min,
Powerade = 62.2 ± 4 min, p= 0.365). Exercise induced a similar
reduction in body mass (cow’s milk = 2.0 ± 0.3%, soy milk 1.9 ±
0.2%, Sustagen Sport = 1.9% ± 0.2%, Powerade = 2.0% ± 0.3%).
Beverage volume and consumption
Similar beverage volumes were consumed across all experimen-
tal conditions (cow’s milk = 2.2 ± 0.4 L, soy milk = 2.2 ± 0.2 L,
Sustagen Sport = 2.2 ± 0.3 L, Powerade = 2.2 ± 0.3 L). Because of
volume tolerance issues, approximately half the participants re-
quired slightly longer than the allocated1htoconsume the bev-
erages. The longest time required to consume the test beverages
for all trials was 75 min. For all trials where >1 h was required to
complete beverage ingestion, outcome measures were taken rel-
ative to the commencement of drinking. Two trials had to be
repeated because of emesis.
Outcome measures
Net body mass results are displayed in Fig. 1. All experimental
trials concluded with participants in a state of negative net body
mass relative to pre-exercise values (Sustagen Sport = –0.48 ±
0.39 kg, soy milk = –0.78 ± 0.37 kg, cow’s milk = –0.92 ± 0.48 kg,
Powerade = –1.37 ± 0.3 kg). The consumption of Powerade resulted
in significantly greater net body mass loss when compared with
all milk beverages (Powerade vs cow’s milk, p< 0.01; Powerade vs
soy milk, p< 0.01; Powerade vs Sustagen Sport, p< 0.01). Differ-
ences between Powerade and all milk beverages were evident 2 h
after beverage consumption and following1hintheSusagen
Sport trial. Net body mass was also significantly greater for Sustagen
Sport compared with cow’s milk, but not soy milk (cow’s milk vs
Sustagen Sport, p< 0.05; soy milk vs Sustagen Sport, p= 0.158). The
1368 Appl. Physiol. Nutr. Metab. Vol. 39, 2014
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differences between cow’s milk and Sustagen Sport were evident 1 h
after beverage consumption.
The total urine volumes and percentage of fluid retained for
each trial are shown in Table 2. Hourly urine volumes for each
trial are shown in Fig. 2. All milk trials concluded with signifi-
cantly less urine output compared with the Powerade trial (Pow-
erade = 1834 ± 427 mL vs cow’s milk = 1338 ± 578 mL (p< 0.01), vs
soy milk = 1144 ± 446 mL (p≤ 0.01), vs Sustagen Sport = 771 ± 367 mL
(p< 0.01)). Additionally, the total urine output following the
Sustagen Sport trial was significantly less than observed in cow’s
milk (p< 0.01) and soy milk (p< 0.05) trials. Peak urine output
occurred in the first hour of recovery for all trials (Powerade =
868 ± 362 mL, cow’s milk = 747 ± 409 mL, soy milk = 570 ± 361 mL,
Sustagen Sport = 348 ± 272 mL) and remained significantly higher
in the second hour for Powerade compared with the milk trials.
Table 3 displays changes in plasma volume across time. As ex-
pected, plasma volume decreased after exercise-induced dehydra-
tion. Rehydration resulted in an increase in plasma volume from
postexercise measures. Plasma volume shifts from the end of re-
hydration to the conclusion of the observation period did not
differ between trials (all p> 0.05).
Blood measures of sodium, potassium, and glucose remained
within appropriate reference ranges throughout each trial. The
only difference in blood measures between trials occurred in glu-
cose concentration at the completion of trials (Fig. 3). Soy milk
resulted in higher blood glucose concentrations than the 3 other
beverages (soy milk = 5.25 ± 0.42 mmol·L
−1
, cow’s milk = 4.76 ±
0.18 mmol·L
−1
, Sustagen Sport = 4.67 ± 0.39 mmol·L
−1
, Powerade =
4.60 ± 0.37 mmol·L
−1
,p< 0.05).
Palatability ratings revealed participants considered the Powerade
beverage to be the most pleasant and the soy milk the least pleasant
when compared with the other beverages (end of drinking rating,
Powerade = 83 ± 11 mm, cow’s milk = 53 ± 22 mm, soy milk = 14 ±
18 mm, Sustagen Sport = 53 ± 28 mm, all p> 0.05). Sustagen Sport and
Powerade beverages were rated significantly sweeter than the cow’s
milk and soy milk beverages at both rehydration phase check points
(p< 0.05). Subjective ratings of saltiness and bitterness did not differ
between beverage treatments.
GI tolerance questions revealed that ratings of thirst increased
in all trials throughout the recovery phase (p< 0.01) but were not
different between the beverages (p> 0.05). A significant effect of
time (p< 0.01), beverage (p< 0.01), and a time × beverage (p< 0.05)
interaction was observed in subjective ratings of fullness. Post hoc
analysis revealed higher ratings of fullness for Sustagen Sport
compared with all other beverages and that both cow’s milk and
soy milk were rated higher than Powerade across all time points.
A significant effect of time (p< 0.01), beverage (p< 0.01), and a time ×
beverage (p< 0.05) interaction was observed in subjective ratings
of hunger. Post hoc analysis revealed higher ratings following the
Powerade trial compared with all other beverages until the final
hour of the recovery period. Ratings of hunger following the cow’s
milk trial were also higher than for both Sustagen Sport and soy
milk across this period. No significant effects were observed for
any of the other subjective rating measures.
Discussion
The purpose of this study was to compare the effectiveness of
soy milk and a commercially available milk-based liquid meal
supplement with cow’s milk and a carbohydrate–electrolyte drink
for replacing exercise-induced fluid losses. The results of this in-
vestigation demonstrate that consumption of a milk-based liquid
meal supplement following exercise results in improved fluid reten-
tion when compared with cow’s milk, soy milk, and a carbohydrate–
electrolyte drink. Additionally, cow’s milk and soy milk were
similarly effective at enhancing fluid restoration in comparison
with the carbohydrate–electrolyte drink.
Fig. 1. Net body mass responses to the consumption of 4 beverages following an exercise-induced fluid loss. a, Statistically significant
difference between Powerade (Coca Cola Ltd) and Sustagen Sport (Nestle). b, Statistically significant difference between Powerade and cow’s
milk. c, Statistically significant difference between Powerade and soy milk. d, Statistically significant difference between cow’s milk and
Sustagen Sport. Post Ex, postexercise; Pre Ex, pre-exercise.
Table 2. Cumulative urine output and fluid retention at the conclu-
sion of a 4-h period in response to the consumption of 4 beverages
following an exercise-induced fluid loss.
Output (mL) Fluid retention (%)
Beverage Mean SD Mean SD
Powerade 1833b 427 16.6b 16.5
Cow’s milk 1338ab 578 40.0ab 24.9
Soy milk 1143ab 446 46.9ab 19.9
Sustagen Sport 771a 367 65.1a 14.7
Note: Fluid retention = (volume of beverage consumed − urine output after
4 h) × 100. a, Mean statistically significantly different from Powerade. b, Mean
statisitically significantly different from Sustagen Sport.
Desbrow et al. 1369
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The rehydration potential of beverages used in the current
study demonstrated dose–response relationships for total calorie
density, total protein, and sodium. Beverage protein and sodium
content have previously demonstrated a capacity to positively
influence postexercise fluid retention when examined in isolation
(James et al. 2011;Maughan and Leiper 1995;Shirreffs et al. 1996).
Furthermore, higher caloric meals typically slow the rate of gas-
tric emptying, which is likely to improve the capacity to absorb
and retain fluid from the small intestine (Kwiatek et al. 2009). In
contrast, the potential of increases in carbohydrate to contribute
to fluid loss via effects on fluid delivery have been demonstrated
(Jeukendrup et al. 2009). The results from the present study are
generally in keeping with these findings. Given that, the intention
of this experiment was to explore the rehydration potential of
commercially available beverages; the beverages were not pre-
cisely matched for energy and macronutrient distribution, mak-
ing extrapolation to the individual macronutrient effects on fluid
restoration difficult.
The cow’s milk and soy milk beverages in the current investi-
gation had similar energy, macronutrient distribution, and so-
dium, but differed in the source of protein (cow’s milk protein,
and soy protein). Two previous studies to have investigated the
impact of milk proteins on postexercise hydration demonstrated
improved fluid retention when 25 g of whole milk protein was
added to an isocaloric carbohydrate–electrolyte solution (James
et al. 2011) and no effect when a smaller protein dose (15 g) was
added as whey–protein isolate (James et al. 2012). Given that we
saw similar changes in fluid retention after the consumption of
⬃66 g of cow and soy protein within these milk beverages, it is
likely that the amount of protein (rather than the source) is a
significant factor determining the rehydration potential of a bev-
erage. Furthermore, the results of the present study indicate that
the use of soy milk and milk-based meal replacement drinks,
which are widely available and do not require refrigeration, offer
an effective fluid replacement alternative for individuals intoler-
ant to lactose or lacking the facilities to keep beverages cold.
The design of the current investigation required participants to
consume predetermined volumes of temperature-controlled bev-
erages in accordance with rehydration guidelines (Sawka et al.
2007). In the sporting context, athletes typically consume fluids
ad libitum and the beverage choice and total volume consumed
may be determined by many factors, including thirst, palatabil-
ity, gastrointestinal tolerance, drink availability, and dietary
goals (Minehan et al. 2002;Passe et al. 2000). Therefore, it is im-
portant to recognize the practical application of the current re-
sults. First, the findings indicate that the traditional sports drink
was perceived to be the most pleasant of the beverages and soy
milk the least pleasant. While it is possible that the ratings of
Fig. 2. Hourly urine output responses to the consumption of 4 beverages following an exercise-induced fluid loss. a, Statistically significant
difference between Powerade (Coca Cola Ltd) and Sustagen Sport (Nestle). b, Statistically significant difference between Powerade and cow’s
milk. c, Statistically significant difference between Powerade and Soy milk. d, Statistically significant difference between cow’s milk and
Sustagen.
Table 3. Change in plasma volume throughout an observation period in response to the consumption of 4 beverages
following an exercise-induced fluid loss.
Pre-Ex to
Post-Ex (%)
Post-Ex to
rehydration (%)
Rehydration to
1 h (%)
Rehydration to
4 h (%)
Trial Mean SD Mean SD Mean SD Mean SD
Powerade −5.45 9.0 5.49 20.7 1.59 14.8 2.70 6.8
Cow’s milk −1.86 6.3 −1.49 2.0 7.30 9.4 4.01 5.0
Soy milk −4.09 6.6 −2.00 3.6 4.69 8.4 4.99 7.5
Sustagen Sport −5.73 9.4 −0.19 6.3 2.80 4.9 6.28 9.2
Note: Plasma volume changes calculated using the methods of Dill and Costill (1974). No statistically significant differences were
observed. Post-Ex, postexercise; Pre-Ex, pre-exercise.
1370 Appl. Physiol. Nutr. Metab. Vol. 39, 2014
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pleasantness associated with soy milk consumption observed in
the current study relate to the use of participants who were not
regular consumers of soy-based milk products, it is plausible that
the use of soy milk-based beverages for rehydration purposes may
be compromised by palatability issues. Furthermore, the con-
sumption of large volumes of a high calorie milk-based supple-
ment (often providing ≥8000 kJ) within ⬃1 h of exercise is
impractical for many athletes, particular those requiring or habit-
ually consuming a constrained energy intake. With participants
reporting increased satiety associated with the higher calorie
density beverages within this study, the impact of palatability
and tolerance on consumption volumes within an ad libitum
environment warrant further examination.
In summary, this investigation further demonstrates the capac-
ity of commercially available milk-based beverages to enhance
the replacement of lost fluid following exercise in comparison
with carbohydrate–electrolyte drinks. Additionally, the choice of
cow’s milk over soy milk beverages should be based on personal
preference as both have equally effective rehydration potential
when matched volumes are consumed.
Acknowledgements
The authors would like to acknowledge the valuable contribu-
tion made by all study participants. Funding was from internal
Griffith University support. There are no external funding or con-
flict of interest to disclose. Author contributions: B.D., S.J.,
M.D.L., and C.I. were all involved in the conception and design.
S.J., A.B., and C.I. were responsible for the acquisition of data. All
authors contributed to the analysis and interpretation of data. All
authors contributed to drafting the article and revising it criti-
cally for important intellectual content. All authors were involved
in the final approval of the published version of the manuscript.
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