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
- Male recreational endurance exercisers
- Endurance exercise training more than four days per week, more than 60 minutes each day, for at least six years.
Not specified.
Design
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Non-randomized clinical trial
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All subjects completed a seven-day food diary in the pre-test period
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Tests were performed before and immediately after the seven-day Zone diet intervention
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Tests performed are described below.
Intervention
Use of the Zone diet for seven days (CHO:PRO:FAT ratio is 40:30:30).
Statistical Analysis
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One-tailed Student's T-test
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Two-way ANOVA with repeated measures for blood data, macronutrient contributions to the diet and heart rate values
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Fisher's post-hoc test used to determine significance in the ANOVA test.
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.
- 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.
Location
Kingston, United Kingdom.
Variable
|
Pre-Treatment (mean±SE)
|
Post-Treatment (mean±SE)
|
P-Value
|
VO2max (mL/kg*min)
|
54.6±3.1
|
53.9±3.1
|
0.401
|
Time to exhaustion (min)
|
37.68±8.6
|
34.11±7.01
|
<0.05
|
Repiratory Exchange Ratio (RER)
|
0.933±0.029
|
0.946±0.026
|
>0.5
|
Body weight (kg)
|
70.7±2.1
|
69.8±2.1
|
<0.02
|
Body fat (%)
|
15.3±3.1
|
14.7±3.3
|
<0.02
|
Lean body mass (kg)
|
66.4±1.1
|
64.6±1.3
|
<0.06
|
Dietary Variable
|
Normal Diet
|
Zone Diet
|
Carbohydrate (g)
|
296±53.85
|
172±37.54
|
Fat (g)
|
55±17.05
|
58±12.65
|
Protein (g)
|
98±20.46
|
129±28.53
|
Total energy (kcal)
|
2,314±334.35
|
1,994±437.71*
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*Significantly different than normal diet, P<0.04Mean±SD
Other Findings
- Normal Diet (CHO:FAT:PRO)=54:22:24
- Zone Diet (CHO:FAT:PRO)=36:27:37.
- 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.
University/Hospital: | Kingston University, University of Bath (both UK) |
Quality Criteria Checklist: Primary Research
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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 | |