NAP: Energy Balance and Body Composition (2014)


Kerksick CM, Rasmussen CJ, Lancaster SL, Magu B, Smith P, Melton C, Greenwood M, Almada AL, Earnest CP, Kreider RB. J Strength Cond Res. 2006; 20 (3): 643-653.

Study Design:
Randomized Controlled Trial
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To examine the effects of whey protein supplementation on body composition, muscular strength, muscular endurance and anaerobic capacity during 10 weeks of resistance training.

Inclusion Criteria:
  • No current or past use of anabolic steroids
  • Experienced with resistance training of more than one year and training more than three hours per week with a program that included both the bench press and leg press or squat exercises
  • Willing to refrain from non-leisure endurance training for more than 20 minutes during the study
  • Have not ingested creatine, HMB, thermogenics or any ergogenic levels of any nutritional supplements for an eight-week period and have not taken any nutritional supplements or non-prescription drugs during the study
  • Agree to a pre-determined workout program
  • Avoid any regular nutritional practices that might confound the results.
Exclusion Criteria:
  • Females
  • Any existing medical conditions that would compromise participation in the study.
Description of Study Protocol:
  • Recruitment: Not described 
  • Design: Double-blind, placebo-controlled, randomized trial; subjects matched according to fat-free mass and age
  • Blinding used: Double blind.


Supplementation of normal diet during 10-week training program with one of three supplement groups:

  1. Whey protein (40g) plus three grams branch chain amino acids (BCAAs) plus five grams L-glutamine (WBG)
  2. 40g whey protein plus eight grams casein (WC)
  3. 48g carbohydrate placebo (P).

All supplements were in powder form of similar smell, consistency and texture and were packaged in a blinded fashion in individual foil packets. Covance Labs verified the contents. Subjects were seen weekly to determine frequency or severity of side effects and compliance. 

Statistical Analysis

  • All criterion-dependent variables were analyzed by separate univariate analysis of variance (ANOVA) with repeated measures
  • Dietary intake (calorie, CHO, protein and fat) were evaluated by individual two-way (group-x-test) ANOVA
  • Post-hoc procedures were conducted when necessary using Tukey post-hoc procedures
  • Delta scores (post-pre values) were calculated on selected variables and analyzed by one-way ANOVA for further interpretation of these data.
Data Collection Summary:

Timing of Measurements

  • Baseline and after five weeks (T1) and 10 weeks (T2) of training and supplementation
  • Additionally, food records were kept during Weeks Two and Eight.  

Dependent Variables

  • Diet: Four-day food record (three weekdays and one weekend day)
  • Fasting blood for creatine kinase, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, total protein, GGT, Creatinine, BUN, BUN:creatinine ration and uric acid
  • Body mass: Electronic scale 
  • Body water: Bioelectrical impedance analysis
  • Body composition: Dual-energy x-ray absorptiometry (DEXA)
  • One repetition maximum (1RM) strength tests on bench press and leg press (after each respective 1RM test, subjects completed a maximal repetitions to fatigue test with 80% of their pre-determined 1RM)
  • Anaerobic capacity: Computerized 30-second Wingate testing system on a cycle ergometer. 

Independent Variables

Whey protein (40g) plus three grams branch chain amino acids (BCAAs) plus five grams L-glutamine (WBG) or 40g whey protein plus eight grams casein (WC) or 48g carbohydrate placebo (P) supplementation to normal diet.  

Control Variables

Training program

  • Four workouts per week (two upper-body and two lower-body) that primarily utilized multi-joint exercises that targeted major muscle groups
  • Each exercise was to be performed to the point of muscular failure at the last repetition of each set
  • Subjects were instructed to rest for approximately one minute between sets and for two minutes between each exercise
  • Workouts were completed at subject's own training facility and all training compliance and supervision was verified by a training partner, fitness instructor or personal trainer. 
Description of Actual Data Sample:
  • Initial N: 36 males
  • Attrition (final N): 36 males
  • Age: 31.0±8.0 years
  • Ethnicity: Not described
Other relevant demographics
  • Training hours per week-1: 7.7±3.6
  • Training days per week -14.5±0.8
  • Years of training: 5.3±4.4.
  • Height: 179.2±8.0cm
  • Weight: 84.0±12.9 kg
  • Location: Texas.
Summary of Results:


  • There were no significant differences (P>0.05) among groups for total calories, CHO or fat. A significant group difference (P<0.001) for protein was found with WBG (2.12±0.6g per kg-1per day-1; P<0.001) and WC (2.33±0.6g per kg-1per day-1; P<0.001) Groups having higher intakes than P Groups (1.57±0.5g per kg-1per day-1; P<0.001). This finding was due to the additional 48g protein added to the WBG and WC.
  • There was no difference between groups (P>0.05) for upper-body and lower-body total training volume
  • No adverse effects were reported by any of the subjects
  • The WC Group was the only group that showed significant increases (P<0.05) during T1 and T2, compared to T0 for body mass, DEXA total scanned mass, DEXA fat-free mass and DEXA lean mass. No other significant differences were seen between any other body composition or bone mineral variables.
  • Significant increases over time, with no group differences, were found in bench press 1RM, leg press 1RM and leg press lifting volume
  • No significant time or interaction effects (P>0.05) were seen for any of the anaerobic capacity variables
  • No significant changes were observed between groups in blood variables.
Author Conclusion:
  • Supplementing the diet with a protein supplement containing 40g per day-1 of whey and eight grams per day-1 of casein during resistance training improves the training adaptations in comparison to subjects who ingest a carbohydrate placebo or a similar protein group
  • The two types of protein formulation did seem to have varying effects on body composition variables
  • These findings indicate that the potential ergogenic value of protein supplementation during the early phases of training may vary depending on the specific amino acid composition of the supplement.
Funding Source:
Royal Numico
Reviewer Comments:
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? Yes
  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) Yes
  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? N/A
  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.) N/A
  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? Yes
  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%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  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.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  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? N/A
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? N/A
  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? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
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? N/A
  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)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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