Journal of the American College of Nutrition

ISSN: 0731-5724 (Print) 1541-1087 (Online) Journal homepage: http://www.tandfonline.com/loi/uacn20

Hydration Status over 24-H Is Not Affected by Ingested Beverage Composition Matthew A. Tucker MA, Matthew S. Ganio PhD, J. D. Adams MS, Lemuel A. Brown MS, Christian B. Ridings BS, Jenna M. Burchfield BS, Forrest B. Robinson BS, Jamie L. McDermott MS, RD, LDN, Brett A. Schreiber BS, Nicole E. Moyen MS, Tyrone A. Washington PhD, Andrea C. Bermudez BS, Meredith P. Bennett BS & Maxime E. Buyckx MD To cite this article: Matthew A. Tucker MA, Matthew S. Ganio PhD, J. D. Adams MS, Lemuel A. Brown MS, Christian B. Ridings BS, Jenna M. Burchfield BS, Forrest B. Robinson BS, Jamie L. McDermott MS, RD, LDN, Brett A. Schreiber BS, Nicole E. Moyen MS, Tyrone A. Washington PhD, Andrea C. Bermudez BS, Meredith P. Bennett BS & Maxime E. Buyckx MD (2015) Hydration Status over 24-H Is Not Affected by Ingested Beverage Composition, Journal of the American College of Nutrition, 34:4, 318-327, DOI: 10.1080/07315724.2014.933684 To link to this article: http://dx.doi.org/10.1080/07315724.2014.933684

Published online: 19 Mar 2015.

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Date: 21 September 2015, At: 12:35

Hydration Status over 24-H Is Not Affected by Ingested Beverage Composition Matthew A. Tucker, MA, Matthew S. Ganio, PhD, J. D. Adams, MS, Lemuel A. Brown, MS, Christian B. Ridings, BS, Jenna M. Burchfield, BS, Forrest B. Robinson, BS, Jamie L. McDermott, MS, RD, LDN, Brett A. Schreiber, BS, Nicole E. Moyen, MS, Tyrone A. Washington, PhD, Andrea C. Bermudez, BS, Meredith P. Bennett, BS, Maxime E. Buyckx, MD

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Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas (M.A.T., M.S.G., J.D.A., L.A.B., C.B.R., J.M.B., F.B.R., B.A.S., N.E.M., T.A.W., A.C.B., M.P.B.); McDermott Nutrition, Fayetteville, Arkansas (J.L.M.); The Coca-Cola Company, Atlanta, Georgia (M.E.B.)

Objective: To investigate the 24-h hydration status of healthy, free-living, adult males when given various combinations of different beverage types. Methods: Thirty-four healthy adult males participated in a randomized, repeated-measures design in which they consumed: water only (treatment A), waterCcola (treatment B), waterCdiet cola (treatment C), or waterCcolaCdiet colaCorange juice (treatment D) over a sedentary 24-h period across four weeks of testing. Volumes of fluid were split evenly between beverages within each treatment, and when accounting for food moisture content and metabolic water production, total fluid intake from all sources was equal to 35 § 1 ml/kg body mass. Urine was collected over the 24-h intervention period and analyzed for osmolality (Uosm), volume (Uvol) and specific gravity (USG). Serum osmolality (Sosm) and total body water (TBW) via bioelectrical impedance were measured after the 24-h intervention. Results: 24-h hydration status was not different between treatments A, B, C, and D when assessed via Uosm (590 § 179; 616 § 242; 559 § 196; 633 § 222 mOsm/kg, respectively) and Uvol (1549 § 594; 1443 § 576; 1690 § 668; 1440 § 566 ml) (all p > 0.05). A -difference in 24-h USG was observed between treatments A vs. D (1.016 § 0.005 vs. 1.018 § 0.007; p D 0.049). There were no differences between treatments at the end of the 24-h with regard to Sosm (291 § 4; 293 § 5; 292 § 5; 293 § 5 mOsm/kg, respectively) and TBW (43.9 § 5.9; 43.8 § 6.0; 43.7 § 6.1; 43.8 § 6.0 kg) (all p > 0.05). Conclusions: Regardless of the beverage combination consumed, there were no differences in providing adequate hydration over a 24-h period in free-living, healthy adult males. This confirms that beverages of varying composition are equally effective in hydrating the body.

INTRODUCTION

toward maintaining a euhydrated state [16,17]. However, intake guidelines from the Institute of Medicine (IOM) [18] highlight the reality that a significant contribution to daily fluid intake will likely come from beverages other than drinking water, possibly in the realm of 44% of total fluid intake [19]. Studies documenting the acute diuretic effects of caffeine ingestion [20,21] have led some to recommend avoiding consumption of caffeine when trying to maintain eyhudration, particularly among active individuals [22,23]. Given that an estimated 20 to 30% of Americans consume upwards of 600 mg of caffeine daily from various beverages [24], it is important to consider the potential ability of these beverage types to contribute toward achieving free-living euhydration. Recently, the IOM provided guidelines for adequate daily fluid intake based off a substantial data set [18]. With a range of daily fluid intake from all sources of 1.4 to 7.7 l, the median

Though an extensive body of literature exists regarding the relationship between beverage composition and hydration status during prolonged exercise (60 minutes) [1–6] and rehydration over several hours postexercise [7–13], relatively little is known about this relationship when examining individuals over a longer period of time (i.e., 24 hours) in a healthy, freeliving adult population. Daily fluid intake guidelines, at times, neglect the potential ability of beverages other than water to aid in providing adequate hydration, despite beverages containing a high (>85%) water content [14]. Current guidelines on daily fluid intake, such as the well-known 8 £ 8 rule (drinking 8 fluid ounces of water 8 times per day) [15], are often interpreted as plain water being the only fluid that provides a meaningful contribution

Address correspondence to: Matthew S. Ganio, PhD, Human Performance Laboratory, University of Arkansas, 155 Stadium Dr., HPER 321, Fayetteville, AR 72701. E-mail: [email protected]

Journal of the American College of Nutrition, Vol. 34, No. 4, 318–327 (2015) Ó American College of Nutrition, Published by Taylor & Francis Group, LLC 318

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24-Hour Hydration Status and Beverage Composition values of 3.7 and 2.7 L/d for males and females, respectively, were set as the suggested adequate daily intake. An absolute fluid volume recommendation fails to consider that different body sizes require different fluid volumes to maintain euhydration. In clinical practice, daily fluid volume recommendations are often made relative to body mass. Mudge and Weiner suggest a “normal” daily fluid requirement of approximately 2500 ml (from ingested fluids, foods, and metabolic production), which equates to 35.7 ml/kg body mass for a 70 kg male adult [25]. Following similar methodology, various authors’ estimates of daily fluid requirements have ranged from 30 to 45 ml/kg body mass [26–29]; however, the exact origin of some of these estimates is unknown [30]. Grandjean et al. investigated the effect of various beverage combinations on the hydration status of healthy, free-living adult males [31]. With a total daily fluid intake of 35 ml/kg body mass (including fluids from food and accounting for metabolic water production), subjects consumed either water alone or various combinations of equal amounts water plus caffeinated caloric or noncaloric cola, orange juice, or coffee over a 24-hour period. Although the authors noted the data as preliminary due to a relatively small sample size (n D 18), results showed that regardless of the beverage type consumed, urine and blood markers of 24-hour hydration status were not different between treatment groups. The present study extends upon the findings of Grandjean et al. [31] by utilizing a larger sample size (n D 34) and more accurately estimating fluid from food composition by providing food to the subjects during the intervention. Given that there is no gold standard for hydration assessment [32], we have also expanded our hydration assessment to include estimates of intra- and extra-cellular fluid volume via bioelectrical impedance. The purpose of the present study was two-fold: to (1) investigate the effectiveness of a previously suggested daily fluid intake value (35 ml/kg body mass) [25] in providing adequate hydration in healthy free-living males and (2) determine whether differences in 24-hour hydration status exist when healthy freeliving males are provided with various beverage combinations.

MATERIALS AND METHODS Subjects Thirty-four healthy adult males (age 23.6 § 4.7 years; height 178.5 § 7.2 cm; mass 76.0 § 12.1 kg; body mass index 23.8 § 3.4 kg/m2) from northwest Arkansas volunteered to participate in the study. Subjects were recruited through a university-wide e-mail system and flyer postings. Subjects were deemed eligible to participate after taking part in an in-person interview where the criteria of the study and subjects’ medical history were discussed. To be considered eligible, subjects were required to be non-obese (body mass index < 30 kg/m2), have a stable body weight, be willing to abstain from caffeine

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and alcohol on specific days over the testing period, use caffeine in moderation ( 0.05; see Table 1).

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Body Mass and BIA Pre- and post-treatment (i.e., Wednesday morning vs Thursday morning) body mass and BIA results are presented in Table 2. No differences between treatments were observed with regard to body mass, total body water, intracellular water, or extracellular water (all p > 0.05). Calculated grand means of pre- and post-treatment values across all beverage treatments also revealed no differences in body mass (76.6 § 12.2 vs 76.5 § 12.1 kg, respectively), total body water (43.8 § 6.0 vs 43.8 § 5.9 kg), intracellular water (25.6 § 3.0 vs 25.6 § 3.0 kg), or extracellular water (18.2 § 3.0 vs 18.2 § 3.0 kg; all p > 0.05).

Urinary Indices of Hydration Status Pre- vs post-treatment urinary indices of hydration status are presented in Table 3. No main effects or interaction (Day £ Treatment) were observed with regard to volume or color (p > 0.05); however, creatinine was significantly higher posttreatment (p D 0.013). Post-treatment differences were observed between Txt A and Txt D USG (p D 0.003), osmolality (p D 0.008), sodium (p D 0.047), and potassium (p D 0.048). Similarly, post-treatment values for Txt C differed from Txt D with regard to USG (p D 0.004), osmolality (p D 0.006), sodium (p D 0.001), potassium (p < 0.001), and chloride (p < 0.001). Within a given treatment there were few changes pre- to post-intervention. In Txt B, pre- to post-intervention changes occurred with USG (p D 0.039) and urine osmolality (p D

0.050). In Txt C, pre- to post-intervention changes occurred with potassium (p D 0.005) and chloride (p D 0.047). In Txt D, pre- to post-intervention changes occurred with sodium (p D 0.008), potassium (p D 0.039) and chloride (p D 0.037). Initial analyses of 24-hour urinary variables indicated differences between treatments in urine volume (p D 0.020); however, follow-up tests did not reveal differences between any two treatments (p > 0.05; Table 4). Twenty-four hour USG was different between Txt A and Txt D (p D 0.049). No differences between treatments were observed in 24-hour values of volume, osmolality, sodium, potassium, chloride, or creatinine (all p > 0.05; Table 4).

Blood Measures Pre- and post-treatment blood markers of hydration status are presented in Table 5. Between treatments, no differences were observed in serum osmolality, serum sodium, serum potassium, serum chloride, serum urea, serum creatinine, hemoglobin, or hematocrit (all p > 0.05). Independent of treatment, serum sodium pre-treatment was significantly greater than post-treatment (141.8 § 1.9 vs 141.3 § 1.6 mmol/L, respectively; p D 0.008). Additionally, independent of treatment, serum protein pre-treatment was significantly lower than post-treatment (6.74 § 0.96 vs 6.95 § 0.98 ug/L, respectively; p D 0.023) and pre-treatment serum creatinine was significantly lower than post-treatment (1.36 § 0.18 vs 1.54 § 0.21 mg/dl, respectively; p < 0.001).

DISCUSSION In the present study, subjects were provided with various combinations of caffeinated caloric and noncaloric cola, orange juice, and water to consume over a 24-hour period. Using a relatively large sample size (n D 34) and controlling for fluid intake from food, we were able to demonstrate that ingested beverage composition does not affect 24-hour hydration status in healthy, free-living adult males when total daily fluid intake is equal to 35 ml/kg body mass. Further, total daily

Table 2. Pre- vs Post-treatment Measures of Body Mass and BIAa Txt A B C D

Time of Collection Pre Post Pre Post Pre Post Pre Post

Body Mass (kg) 76.6 76.6 76.5 76.5 76.7 76.3 76.6 76.7

§ 12.3 § 12.0 § 12.4 § 12.6 § 12.3 § 12.5 § 12.2 § 11.9

Total Body Water (kg) 43.9 43.9 43.6 43.8 43.9 43.7 43.8 43.8

§ 6.2 § 5.9 § 6.0 § 6.0 § 6.1 § 6.1 § 5.9 § 6.0

Intracellular Water (kg) 25.6 25.6 25.5 25.5 25.6 25.5 25.5 25.6

§ 3.1 § 2.6 § 3.0 § 3.0 § 3.1 § 3.1 § 3.0 § 3.0

Extracellular Water (kg) 18.3 18.3 18.1 18.2 18.3 18.1 18.2 18.2

§ 3.1 § 3.0 § 3.0 § 3.0 § 3.1 § 3.0 § 3.0 § 3.0

BIA D bioelectrical impedance analysis. a No significant differences in pre- vs post-treatment analyses for any variable (all p > 0.05).

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24-Hour Hydration Status and Beverage Composition Table 3. Pre-treatment (Wednesday First Void) vs Post-treatment (Thursday First Void) Urinary Indices of Hydration Status

Txt

Time of Collection

A

Volume (ml)

Pre Post Pre Post Pre Post Pre Post

B C D

352 381 354 348 376 403 351 309

§ 208 § 162 § 208 § 146 § 196 § 172 § 236 § 155

Color 4 3 4 3 3 3 4 4

§2 §1 §1 §1 §2 §1 §2 §1

Specific Gravity 1.021 1.018 1.023 1.019 1.021 1.018 1.021 1.023

§ 0.009 § 0.006b § 0.008c § 0.008 § 0.010 § 0.018b § 0.010 § 0.007

Osmolality (mOsm/kg) 688 613 749 645 712 601 696 755

Potassium (mmol/L)a

Sodium (mmol/L)a

§ 281 § 209b § 286c § 251 § 293 § 246b § 309 § 229

106.6 99.2 115.9 105.8 101.2 81.4 107.4 134.5

§ 62.1 § 51.8b § 56.5 § 59.2 § 45.2 § 40.5b § 44.6b § 46.2

26.6 25.2 30.8 25.9 34.4 20.9 27.1 34.8

Chloride (mmol/L)a

§ 14.9 § 12.9b § 19.8 § 11.9 § 21.3d § 13.4b § 16.7b § 19.0

115.0 105.6 122.0 108.0 114.9 87.0 113.7 128.8

Creatinine (mg/dl)a

§ 53.8 § 46.1 § 48.8 § 46.3 § 38.9d § 29.2b § 35.1b § 34.4

176.3 146.7 188.6 150.1 186.2 132.4 172.0 158.1

§ 78.8 § 56.8 § 82.6 § 58.8 § 81.5 § 56.4 § 90.7 § 64.6

n D 25. Significantly different from post-treatment D (p < 0.05). c Significantly different from post-treatment B (p < 0.05). d Significantly different from post-treatment C (p < 0.05). a

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b

because fluid consumption prior to the pre-intervention sample was ad libitum. This variability may explain some of the differences observed pre- to post-intervention (Table 3) but, interestingly, all of the post-intervention differences indicate an improved hydration status. This indicates that ad libitum fluid intake likely was insufficient to maintain euhydration (known as involuntary dehydration [39]), and with the controlled fluid intake of 35 ml/kg body mass, hydration status was improved (as indicated in the post-intervention samples). In order to provide more insight into hydration status over the full 24 hours, subjects collected all of their urine over the intervention period. With this we were able to classify the 24hour hydration status of subjects through analysis of several validated indices. A recent longitudinal study by Armstrong et al. provided suggested references for classifying free-living hydration status in healthy adults [35]. Euhydration was defined by the following criteria: fluid intake 2108–2249 ml/24-h, urine volume 1377–1533 ml/24-h, 24-hour USG 1.018–1.020, 24hour urine osmolality 637–720 mOsm/kg, and 24-hour urine color 4–5 [35]. With specific attention to USG, there appears to be a general consensus that a value of less than 1.020 constitutes a euhydrated state [33,37,40]. In the present study, grand means (i.e., across all beverage conditions combined) were 1.017 § 0.007 for 24-hour USG, 599 § 211 mOsm/kg for 24hour urine osmolality, 1531 § 604 ml for 24-hour urine volume, and 3 § 1 for 24-hour urine color. These values indicate that subjects in the present study were euhydrated with the

fluid intake from all sources equivalent to 35 ml/kg body mass was sufficient to keep these subjects in a euhydrated state.

Classification of Hydration Status It is generally accepted that there is no single universal laboratory method to classify an individual’s hydration status [34,35]. Further, classification of hypohydration or hyperhydration will ultimately depend on what the physiological definition of euhydration is, which has its difficulties given that it is a dynamic state [36]. Spot samples of urine or blood are often used as indicators of hydration status, with some shortcomings. A single time point measurement of urine is somewhat indicative of hydration status but is a delayed measure [32,37]. In other words, improved hydration status would not be reflected in a urine sample for several hours. Single blood measures are somewhat more responsive to changes in hydration status [37] but are only indicative of current hydration status and not what has occurred over 24 hours. Despite these shortcomings, we obtained spot samples pre- and post-intervention because these are commonly measured, and they also provide the ability to assess more markers of hydration (especially in the blood). For example, serum osmolality is widely used as a key circulatory index of hydration status, largely due to the role of extracellular osmolality in stimulating fluid regulatory mechanisms [38]. It is not surprising that there was more variability in these measures between treatments, especially

Table 4. 24-Hour Urine Measures during Controlled Fluid Intake (Wednesday to Thursday Morning) Txt Volume (mL) Color Specific Gravity Osmolality (mOsm/kg) Sodium (mmol/L) Potassium (mmol/L) Chloride (mmol/L) Creatinine (mg/dl)a A B C D

1549 1443 1690 1440

§ 594 § 576 § 668 § 566

3 3 3 3

§1 §1 §1 §1

1.016 1.017 1.016 1.018

§ 0.005 § 0.007 § 0.006 § 0.007b

590 616 559 633

§ 179 § 242 § 196 § 222

109.4 118.0 115.1 127.2

§ 41.5 § 46.0 § 41.9 § 46.5

33.5 33.3 32.4 37.5

§ 15.3 § 13.5 § 15.2 § 15.4

116.9 122.5 117.3 130.0

§ 37.7 § 41.6 § 37.0 § 38.4

119.3 128.3 116.6 132.8

§ 41.6 § 52.0 § 46.0 § 54.2

n D 30. Significantly different from treatment A (p D 0.049).

a

b

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24-Hour Hydration Status and Beverage Composition Table 5. Pre- vs Post-treatment Blood Indices of Hydration Statusa

Txt A B C D a

Time of Collection Pre Post Pre Post Pre Post Pre Post

Serum Osmolality (mOsm/kg) 291 291 292 293 291 292 292 293

§4 §4 §5 §5 §5 §5 §6 §5

Serum Sodium (mmol/L) 141.6 141.1 142.0 141.6 141.6 141.1 142.0 141.2

§ 1.4 § 1.4 § 2.1 § 1.9 § 2.1 § 1.7 § 2.1 § 1.5

Serum Potassium (mmol/L) 4.4 4.3 4.4 4.4 4.4 4.3 4.4 4.3

§ 0.4 § 0.4 § 0.4 § 0.4 § 0.5 § 0.3 § 0.5 § 0.5

Serum Chloride (mmol/L) 102.9 102.9 102.9 102.9 102.7 102.6 103.0 102.4

§ 1.6 § 1.6 § 1.9 § 1.8 § 2.0 § 1.6 § 1.9 § 1.8

Serum Urea Nitrogen (mg/dl)b

Serum Creatinine (mg/dl)b

15.5 § 3.3 14.8 § 3.1 15.0 § 3.0 14.7 § 2.8 15.6 § 2.4 14.9 § 2.3 15.7 § 2.4 15.7 § 2.8

1.35 1.50 1.33 1.56 1.38 1.56 1.37 1.53

§ 0.20 § 0.20 § 0.14 § 0.20 § 0.18 § 0.22 § 0.19 § 0.21

Serum Protein (mg/ml)b 6.60 6.86 6.74 6.94 6.67 7.11 6.93 6.88

§ 1.05 § 1.14 § 0.76 § 0.96 § 0.97 § 1.02 § 1.05 § 0.79

Hemoglobin (g/dl) 14.7 14.8 14.7 14.7 14.6 14.7 14.6 14.7

§ 0.8 § 0.9 § 0.9 § 0.8 § 0.9 § 0.8 § 0.8 § 0.8

Hematocrit (%) 44.9 45.1 45.2 44.7 45.0 44.8 45.2 45.0

§ 2.2 § 2.6 § 2.2 § 2.4 § 2.5 § 2.4 § 2.0 § 2.4

No significant differences for any variable (all p > 0.05). n D 33.

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b

24 hours of beverage intervention. Importantly, subjects were prohibited from engaging in physical activity (outside of activity associated with normal daily living) during the intervention phase of each week (all day Wednesday and Thursday prior to laboratory measures) to limit potential sweat losses and subsequent increased fluid turnover. If subjects were performing physical activity during this period, it is possible that total daily fluid intake equal to 35 ml/kg body mass would not be sufficient to achieve euhydration. Hydration status of our subjects following 24-hours of beverage intervention are similar to those previously reported by Grandjean et al. [31] with respect to USG, 24-hour urine volume, and urine osmolality; however, the previous authors observed a mean body mass loss of 0.30% following beverage intervention, which was suggested to be indicative of very slight dehydration occurring [31]. Though not clinically significant, the authors suggest that the difference in body mass could be attributed to several factors, including the possibility of insufficient fluid intake or simply normal individual variability. Body water balance can vary in normal, healthy adults by §0.22% ( §165 ml) of body mass in temperate conditions [41]. Data from the present study revealed a decrease in post- vs pre-treatment body mass and total body water of only 0.17 § 0.83% and 0.06 § 2.06%, respectively, further supporting the conclusion that subjects’ hydration status did not change with the beverage intervention, regardless of the treatment they received.

Beverage Composition Given that no differences in hydration status were observed between beverage treatments (Table 4), it would be pertinent to consider the differences in beverage composition and how this may have affected the results. In terms of water in its plain form, Txt A was the only condition in which subjects received all of their fluids from beverages in the form of bottled water. In Txt B and Txt C, the contribution to total daily fluid intake from bottled water was 33%, and in Txt D, just 17%. In

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treatments B, C, and D, however, additional beverages also contained high amounts of water, with cola beverages (caloric and noncaloric) composed of 90% water and orange juice 86% water [14]. We did not adjust fluid volumes for the beverages that were not composed of 100% water. Therefore, total absolute water content ingested was marginally lower when ingesting colas and orange juice. Despite this difference, hydration status was not affected; all beverage combinations resulted in a similar hydration status over the 24-hour period. If beverages of different compositions are able to contribute equally to overall hydration status, it suggests that they are likely digested and absorbed at similar rates. Recently, the absorption rate of commercially available carbohydrate sports drinks compared with water was investigated using a deuterium tracer in resting conditions [42]. The rate of absorption time was similar between the carbohydrate beverages vs water; thus, the time it took for 100% absorption was equal between beverage compositions. It should be noted, however, that the carbohydrate concentration of the beverages used was 5–8% and they contained relatively high amounts of sodium (10– 18 mmol/l). These values differ from the beverages used in the present study, with the carbohydrate concentration of the cola and orange juice beverages approximately 11 and 10%, respectively, and sodium content minimal (3–4 mmol/l). Additionally, carbohydrate sports drinks typically contain multiple carbohydrate types, which increases the rate of absorption compared to single carbohydrate-type beverages [43]. Most commercially available colas are composed of a single carbohydrate source, typically cane sugar or high-fructose corn syrup. It has previously been demonstrated that beverages containing carbohydrate concentrations greater than~8% may actually delay gastric emptying [43]; however, most studies examining the absorption rate of carbohydrates do so over a period of minutes up to several hours [42,44,45]. Therefore, over 24 hours, there are likely negligible differences in digestion and absorption. This is supported by our data showing few differences in urinary markers of hydration status over 24 hours with various beverages (Table 4).

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24-Hour Hydration Status and Beverage Composition Caffeine in particular is often linked with a diuretic effect [24]; however, data suggest that the response of caffeineinduced diuresis is related to a number of factors [46,47]. Recently, several indices of hydration status were analyzed over 11 days of controlled caffeine ingestion [46]. Separating 59 subjects into 3 treatment groups that received either 0, 3, or 6 mg caffeine/kg/d, multiple 24-hour urinary and blood measures of hydration status were analyzed at consistent intervals over the data collection period. Results showed no differences between treatment groups in 24-hour measures of hydration status, including urine volume, USG, and serum osmolality. Data from the present study support the notion that ingestion of caffeinated beverages does not lead to a hypohydrated state following 24 hours of controlled fluid intake. Subjects received an average caffeine dose of 1.04 § 0.12 mg/kg body mass in Txt B, 1.72 § 0.20 mg/kg body mass in Txt C, and 1.36 § 0.18 mg/kg body mass in Txt D (see Table 1). Values of USG, urine osmolality, serum osmolality, and 24-hour urine volume remained consistent across beverage treatments, further supporting published data that suggest that initial beliefs in the diuretic effect of caffeine may need clarification [31,46,47].

Fluid Intake Recommendations At present, a number of guidelines for free-living daily fluid intake exist in the lay press and scientific literature, including the 8 £ 8 rule [15,48], 3.7 and 2.7 L/d for males and females, respectively [18], and 1 ml/kcal of energy expended (equal to ~2.9 and~2.2 L/d for males and females, respectively) [49]. Interestingly, there is little scientific evidence to support these guidelines [15], although the IOM guideline of 3.7 and 2.7 L/d for males and females is based on a substantial set of selfreported data regarding average daily fluid intake [18]. Further, intake of fluids other than water, such as caffeinated and/or caloric and noncaloric colas, are sometimes neglected as beverages that are capable of providing a meaningful contribution to free-living hydration status. The IOM guideline, however, acknowledges that total daily water intake should include drinking water as well as water in foods and water in other beverages [18]. Though the primary intention of this study was not to investigate the validity of current fluid intake recommendations, our data revealed interesting points of discussion. First, total daily fluid intake was calculated following a previously suggested adequate daily intake value [25], such that fluid intake from all sources was equal to 35 ml/kg body mass. Adopting this method led to a mean total daily fluid intake of 2661 § 413 ml, with 1761 § 428 ml from beverages, 597 § 171 ml from foods, and the remaining difference of~300 ml allotted to an estimate of daily metabolic water production. Interestingly, the total daily fluid intake from all sources is considerably less than the value of 3.7 L/d that the IOM suggests for healthy, free-living adult males. Likewise, the National Research

JOURNAL OF THE AMERICAN COLLEGE OF NUTRITION

Council recommendation of ~2.9 L/d is higher than what our subjects received [49]. However, it should be noted that the source of these recommendations comes from much larger data sets that include individuals of all demographics. Further research investigating fluid needs for individuals of various demographics is warranted. When compared to the 8 £ 8 recommendation, our subjects consumed approximately 11 £ 8-oz servings of fluid; however, in fluids from beverages alone, this equated to~7.5 £ 8-oz servings, potentially lending support to the validity of this wellknown mnemonic. In saying this, however, individual differences in water intake from foods may affect daily fluid requirements dramatically, particularly given cultural differences in daily fluid intake obtained from food sources [50]. Data from a study involving U.S. subjects reported 18% of their daily fluid intake from foods [51], whereas a separate study showed that French subjects typically draw 35% from foods [52]. With regard to relative contribution to overall daily fluid intake, previous data from U.S.-based studies has shown that food typically contributes 19–28% [19,53], and fluids from water and other beverages the remainder. Within the contribution of beverages specifically, drinking water can be as low as 28% [19] and as high as 54% [53]. In the present study, ~22% of total daily fluid intake was derived from foods,~66% from ingested beverages, and ~11% estimated metabolic water production. This suggests that the relative contribution of foods and beverages to overall hydration status followed similar trends to what would typically be observed in an uncontrolled, free-living population.

CONCLUSIONS Results from the present study indicate that when total daily fluid intake is equal to 35 ml/kg body mass, ingestion of various combinations of caffeinated caloric and noncaloric cola, orange juice, and water appear not to significantly affect 24hour hydration status in free-living, healthy adult males. Further, when using multiple urinary and circulatory indices of hydration status, daily fluid intake of 35 ml/kg body mass was sufficient to leave subjects in a euhydrated state following beverage intervention when physical activity was prohibited. Additional research is needed to expand on current understanding of the relationship between fluid intake and body fluid balance. First, results from the present study add to the expanding body of literature supporting the ability of caffeinated and caloric and noncaloric colas to aid in providing a meaningful contribution to hydration status. Though not the intention of this study, this has potentially significant implications with regard to free-living daily fluid intake recommendations, perhaps more so with the well-known 8 £ 8 rule, which is often interpreted as plain water only [16,17].

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24-Hour Hydration Status and Beverage Composition Second, future research in the area of fluid balance and beverage ingestion should seek to include female subjects, because current understanding of this relationship in this population is limited. In addition, multiple measures of blood and urine markers throughout a 24-hour period may help provide a clearer view of acute changes in hydration status during beverage intervention.

12.

13.

14.

ACKNOWLEDGMENTS 15.

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We express our sincere gratitude to the subjects for their dedicated participation throughout the duration of the study. 16.

FUNDING This study was supported by a grant from The Coca-Cola Company.

17. 18.

19.

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Received February 19, 2014; accepted June 8, 2014.

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