Hydration and Physical Activity


Ray ML, Bryan MW, Ruden TM, Baier SM, Sharp RL, King DS.  Effect of sodium in a rehydration beverage when consumed as a fluid or meal.  J Applied Physiol 1998; 85(4): 1329-36. 

PubMed ID: 9760324
Study Design:
Randomized Crossover Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To examine the effectiveness of rehydration with 4 different beverages: water, carbohydrate-electrolyte beverage (CE), chicken broth (CB), and chicken noodle soup (Soup) containing high [Na].
Inclusion Criteria:
Physically-active, exercised 3-4 days/week; informed consent; no others mentioned.
Exclusion Criteria:
None mentioned
Description of Study Protocol:

Recruitment 30 (15M, 15 F) recruited to participate in study.


Design randomized crossover; 4 sessions with 1 week between each session; each session composed of thermal- and exercise-induce dehydration followed by 2h rehydration w/1 of the 4 beverage conditions (Water, CE, CB, Soup).


Blinding used (if applicable) not mentioned


Intervention (if applicable) 4 beverage conditions administered during 2 h recovery period: water, CE, CB, Soup


Statistical Analysis Blood measurements blood pressure, rectal temp during rehydration: initial 2-way repeated measures ANOVA, followed by Newman Keuls post hoc tests when needed;

All other data: 1-way ANOVA;

Sig level p<0.05


Data Collection Summary:

Timing of Measurements

Dehydration, 90-120 min: thermal and exercise-induced; overnight fast and 16h after last exercise bout, came to lab, BW obtained; resting blood sample taken; temp probe inserted; 20 min light cycling (50-100W) at 20C followed by 10 min heat exposure (sauna, 65C), repeated alternating exercise and sauna until 2-3% BW lost; temp and HR monitored q. 30 min.  All urine collected and pooled for analysis.

Rehydration, 2h: After 30 min transition period;  catheter inserted for 0.9% NaCl infusion q. 20 min during period; given 1 of 4 beverage conditions consumed immediately and then 20 min later.  Water was then consumed q. 20 min for remainder of period until vol equalled amount of vol water lost during dehydration.  Blood samples, blood pressure, temp at beginning and end of period, urine collected throughout

Dependent Variables

  • Body weight loss
  • Urinary measurements: vol, SG, Osm (vapor pressure osmometer), [Na, K] (urine collected; flame photometry)
  • Intake and output of Na, K (from amount present in beverage and analysis of Urine)

Independent Variables

 Beverage consumed during rehydration period: water, CE, CB, Soup

Control Variables

Controlled temp during dehydration (20oC exercise, 65oC sauna) and rehydration (20oC);

Consumption amounts of beverages (175 mL at beginning and 175 mL 20 min into the rehydration period, equal vol of water at 20 min intervals after beverage was consumed until equalled vol of water lost (BW) during dehydration);

Workloads of activity during exercise (50-100W).

BW lost (2-3%)

Diet and exercise during study - kept diet and exercise patterns constant during the days between treatments.

Description of Actual Data Sample:


Initial N: 30:  15 M, 15 F

Attrition (final N): 15 M, 15 F (Total N = 30)

Age: See anthrometrics table below

Ethnicity: Not mentioned

Other relevant demographics: Physically active


  Age (yr) Weight (kg) Height (cm) BMI (kg/m2)
Men 25±1 82.8±3.2* 179.9±2.3* 25.5±0.6
Women 23±1 61.1±1.3 160.6±2.0 23.8±0.7
Total 24±1 72.0±2.7 170.2±2.3 24.7±0.5
Difference between M & F ns p<0.05 p<0.05 ns

Location: Lab, Iowa State Univ, Iowa, USA


Summary of Results:





CE Soup

Statistical Significance of Group Difference

BW, baseline (kg)



72.0±2.7 72.2±2.7


BW, Dehydrated (kg)



70.2±2.6 70.5±2.6


BW, Rehydrated (kg)



71.6±2.7 71.8±2.7


Uvol (ml) 232.3±31.2 188.2±19.6 309.9±30.2* 231.3±28.6 *p=0.02, sig diff from CB
Specific gravity 1.016±0.001 1.026±0.004 1.020±0.005 1.019±0.001  
Osm, mosm/kg water 491.2±48.9 609.7±39.4** 401.8±51.0 567.6±51.2** **p=0.01, sig diff from CE
[Na], mmol/L 60.9±6.6 87.2±6.7*** 48.0±7.0 90.2±10.7*** ***p=0.0004, sig diff from CE and water
[K], mmol/L 65.4±6.7 88.9±6.3^ 51.4±6.0 68.0±6.2 ^p=0.007, sig diff from water, Soup, CE

Intake: Na, K

0*, 0* 40.7*, 8.9* 6.4*, 1.2* 118.4*, 4.9* *p<0.05, sig diff between groups
Uoutput Na, K 16.2±4.0,  15.2±2.9 16.5±2.2, 16.5±2.0

14.8±3.2,  15.8±3.2

19.7±3.2,  16.4±3.1 ns


Other Findings

NS differences between conditions in temp, blood pressure.

Plasma vol: Decreased 7.0±7% as consequence of dehydration (all trials combined).  At end of rehydration, ns different from prehydration status in CB (-1.6±1.1%) and Soup (-1.4±0.9%), though Pvol remained sig below pre-dehydration in water (-5.6±1.1%) and CE (-4.2±1.0%) (p<0.01).

Plasma Osm: Increase in Posm after heat and exercise-induced dehydration; Posm in CB and CE sig greater than water (p=0.04).

Plasma e-: [Na] incr after dehydration, though ns differences in [Na] between conditions; [K] increased after dehydration.  [K] in Soup 20-120 min sig lower than in CB at 20-120 min, water 40-80 min and 120 min, and CE at 40 min (p<0.05). 

Author Conclusion:

Greater plasma recovery and lower urine volumes observed in subjects ingesting CB and Soup (high [Na]), than in water or CE.  These differences were seen despite the ingestion of only 350 ml of each beverage at the onset of rehydration.  Composition of a fluid consumed immediately after heat- and exercise-induced dehydration has an important impact on body fluid restoration and should be considered if rapid rehydration is a goal.

Although consuming a meal such as Soup has the advantage of providing fluid and electrolytes while minimizing hunger after exercise, additional research in needed to formulate a rehydration beverage containing an optimal combination of electrolytes, CHO, and possibly protein to maximize water resoration. 

Funding Source:
Campbell's Soup Co.
Food Company:
Reviewer Comments:
*see figures for changes in plasma electrolytes over time.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) Yes
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? ???
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? ???
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? ???
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes