NAP: Energy Balance and Body Composition (2007)


Jarvis M, McNaughton L, Seddon A, Thompson D. The acute 1-week effects of the Zone diet on body composition, blood lipid levels, and performance in recreational athletes. J Str Cond Res. 2002; 16 (1): 50-57. 

PubMed ID: 11834107
Study Design:
Non-Randomized Controlled Trial
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To examine the effects of the Zone diet on athletic performance, specifically VO2 max, body composition and time to exhaustion during endurance performance.
Inclusion Criteria:
  • Male recreational endurance exercisers
  • Endurance exercise training more than four days per week, more than 60 minutes each day, for at least six years.
Exclusion Criteria:
None specified.
Description of Study Protocol:

Not specified.


  • Non-randomized clinical trial

  • All subjects completed a seven-day food diary in the pre-test period

  • Tests were performed before and immediately after the seven-day Zone diet intervention

  • Tests performed are described below. 


Use of the Zone diet for seven days (CHO:PRO:FAT ratio is 40:30:30).

Statistical Analysis

  • One-tailed Student's T-test

  • Two-way ANOVA with repeated measures for blood data, macronutrient contributions to the diet and heart rate values

  • Fisher's post-hoc test used to determine significance in the ANOVA test.

Data Collection Summary:

Timing of Measurements

Before and after a seven-day Zone diet intervention.

Dependent Variables

  • Body composition: Bioelectrical impedence analysis
  • VO2max: Incremental treadmill protocol
  • Time to exaustion: Time to voluntary exhaustion during treadmill exercise
  • Biochemical analysis: FFAs, total protein, triglycerides.

Independent Variables

  • Use of the Zone diet for seven days
  • Subjects were given Zone menu to follow.
Description of Actual Data Sample:
  • Initial N: Eight, all male
  • Attrition (final N): Eight
  • Age: 26.1±1.9 years
  • Ethnicity: Not specified.
  • Height: 178±1.7cm
  • Body mass: 70.7±2.1kg
  • VO2max: 54.6±3.1ml per kg per minute.


Kingston, United Kingdom.

Summary of Results:
Pre-Treatment (mean±SE)
Post-Treatment (mean±SE)
VO2max (mL/kg*min)
Time to exhaustion (min)
Repiratory Exchange Ratio (RER)
Body weight (kg)
Body fat (%)
Lean body mass (kg)

Dietary Variable
Normal Diet
Zone Diet
Carbohydrate (g)
Fat (g)
Protein (g)
Total energy (kcal)

*Significantly different than normal diet, P<0.04

Other Findings

  • Normal Diet (CHO:FAT:PRO)=54:22:24
  • Zone Diet (CHO:FAT:PRO)=36:27:37.
Author Conclusion:
  • No improvements in the elements of athletic performance under investigation were seen
  • No evidence was found to support the claims that the Zone diet will improve VO2max or increase the metabolism of FFAs during endurance exercise
  • A significant loss in LBM was seen in the subjects. 
  • The Zone diet's ability to affect body composition is simply a result of its low-energy values placing the body in a state of negative energy balance. 
Funding Source:
University/Hospital: Kingston University, University of Bath (both UK)
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? ???
  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? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
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? N/A
  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? 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? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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? Yes
  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? ???
  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)? Yes
  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? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? No
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? ???
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes