AWM: Low Carbohydrate Diet (2006)
Recruitment
Subjects volunteered for study.
Design
Randomized Crossover Trial.
Blinding used (if applicable)
Not used.
Intervention (if applicable)
Subjects consumed a very-low-carbohydrate diet and a low-fat diet for 2 consecutive 6-week periods.
Statistical Analysis
One-way repeated measures ANOVA was used to evaluate changes over time for all variables. Significant main effects were analyzed further using Fisher least significant difference post-hoc test. Normalized inflammatory biomarkers analyzed with paired Student's t tests.
Timing of Measurements
Subjects consumed 2 weight loss diets for 2 consecutive 6-week periods. Fasting blood samples taken at baseline and after each diet.
Dependent Variables
- Blood samples measured for high-sensitivity IL-6, high-sensitivity TNF-alpha, soluble ICAM-1, soluble P-selectin and high-sensitivity CRP, and determined using ELISA
Independent Variables
- Very-low-carbohydrate (<10% kcals from carbohydrate, 30% protein, 60% fat) or low-fat diet (20% protein, 25% fat and 55% carbohydrate), both designed to be hypoenergetic (-2.1 MJ/day). Energy levels based on nearest 837 kJ increment based on REE obtained with indirect calorimetry. Dietary compliance checked for urinary reagent strips when in ketosis during very-low-carbohydrate diet. Analysis performed on 7 days of diet records at baseline and 21 days during the experimental periods.
Control Variables
Initial N: 15 men
Attrition (final N): 15 men
Age: 33.2 +/- 11.3 years
Ethnicity: Not mentioned.
Other relevant demographics: Body mass: 109.1 +/- 17.8 kg, body fat: 34.9 +/- 5.2%, BMI 34.3 +/- 5.6
Anthropometrics:
Location: University of Connecticut
Baseline | Low-carb | Low-fat | |
Energy MJ |
10.86 +/- 2.47 | 7.77 +/- 1.81 | 6.54 +/- 1.19 |
Protein % |
16 +/- 2 |
28 +/- 5 |
20 +/- 4 |
Carbs % | 47 +/- 5 | 8 +/- 3 | 56 +/- 7 |
Fat % |
35 +/- 4 |
63 +/- 4 |
23 +/- 7 |
Other Findings
Both the very-low carbohydrate diet and low-fat diet resulted in significant decreases in body mass (-6.5 +/- 3.0 kg, P < 0.01, and -3.7 +/- 3.3 kg, P < 0.01, respectively). There was no order effect as to which diet the subject was initially randomized to.
The low carbohydrate diet was significantly different from the low-fat diet for energy, protein, carbohydrate, total fat, saturated fat, polyunsaturated fat and cholesterol (P < 0.05).
Both the low-fat and the very-low carbohydrate diets resulted in significant decreases in absolute concentrations of high-sensitivity tumor necrosis factor-alpha, high-sensitivity interleukin-6, high-sensitivity C-reactive protein, and soluble intercellular cell-adhesion molecule-1.
There was no significant change in absolute soluble P-selectin concentrations after either diet.
Normalized inflammatory values represented as the delta change per 1 kg reduction in body mass showed a significant difference between the 2 diets only for soluble P-selectin (P < 0.05).
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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? | ??? | |
2.2. | Were criteria applied equally to all study groups? | ??? | |
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? | ??? | |
3. | Were study groups comparable? | N/A | |
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.) | N/A | |
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? | Yes | |
6.6. | Were extra or unplanned treatments described? | Yes | |
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? | 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? | 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 | |