HTN: Protein (2007)
Citation:
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare the long-term compliance and effects of two low-fat diets differing in carbohydrate to protein ratio on weight loss, body composition and biomarkers of cardiovascular disease risk in obese subjects with hyperinsulinemia over 68 weeks.
Inclusion Criteria:
- Aged between 20 and 65 years
- Fasting serum insulin level over 12mU per L
- BMI between 27 and 43.
Exclusion Criteria:
Excluded from participation if they had type 2 diabetes, history of clinically significant illness including liver, unstable cardiovascular, respiratory, gastrointestinal disease, malignancy or were pregnant or lactating.
Description of Study Protocol:
- Recruitment: Recruited to participate via public advertisement
- Design: Randomized controlled trial
- Blinding used: Not used
- Intervention: Subjects assigned to either standard protein or high-protein diet for 12 weeks of weight loss and four weeks of weight maintenance and then maintenance for 52 weeks, with minimal professional support.
Statistical Analysis
- Participants failing to complete the entire 68 weeks were excluded from analysis
- Two sets of analyses were conducted
- Univariate ANOVA with repeated measures was used to determine the effects of the treatment, time of measurement and their interactions on the dependent measures
- The between-subjects factors were diet and gender, with the time of measurement as the within-subject factor
- A separate analysis was done using baseline and 68 weeks
- Where ANOVA showed a statistically significant time effect, pairwise comparisons using a Bonferroni correction factor for multiple comparisons was performed
- In the case of a significant diet by time effect, a comparison of diets at each time point and paired T-tests were used to compare means within each group
- Independent Student's T-tests were used to compare group means at baseline, end points and for changes in dependent variables between diets
- The rates of dropouts and difference in characteristics between treatment groups were compared by chi-square tests.
Data Collection Summary:
Timing of Measurements
- Body composition, blood pressure, blood lipids, fasting glucose, insulin, CRP and sICAM-1 were measured at baseline and at Weeks 16 and 68
- Urinary urea-creatinine ratio measured at baseline, Week 16 and at three monthly intervals thereafter.
Dependent Variables
- Body composition through whole-body DEXA
- Venous blood sample for blood lipids, glucose, insulin, C-reactive protein, soluble intracellular adhesion molecule-1 (sICAM-1) and creatinine concentrations
- Body weight measured with subjects wearing light clothing and no shoes
- Urine samples to assess urea-creatinine ratio for dietary compliance
- Body height measured to nearest 0.1cm, using stadiometer
- Blood pressure measured by automated oscillometry.
Independent Variables
- Standard protein (15% protein, 55% carbohydrate, 30% fat) or high-protein diet (30% protein, 40% carbohydrate, 30% fat) during 12 weeks of energy restriction (6.5MJ per day) and four weeks of energy balance (8.3MJ per day), meeting with RD every two weeks
- Followed by 52 more weeks without supplied foods or dietary counseling
- During 12 month follow-up period, subjects completed food frequency questionnaires at three monthly intervals.
Description of Actual Data Sample:
Initial N
- 66 recruited
- Six withdrew before study commencement
- One became pregnant
- One underwent major surgery during study, leaving 58 subjects.
Attrition (Final N)
- 43 completed entire 68 weeks (74% completion)
- 22 in standard protein (seven men, 15 women)
- 21 in high-protein (five men, 16 women)
- 15 had dropped out.
Age
- Standard protein: Mean, 51.5±1.6 years
- High-protein: Mean, 52.0±2.6 years.
Ethnicity
Not mentioned.
Other Relevant Demographics
- Standard protein BMI: 33.6±0.8
- High-protein BMI: 34.6±0.9.
Anthropometrics
There were no statistically significant differences between groups.
Location
Australia.
Summary of Results:
ER | EB | 3M | 6M | 9M | 12M | |
SP-MJ per Day | 6.7±0.2 | 8.5±0.2 | 8.8±0.9 | 8.8±0.8 | 8.3±0.7 | 9.0±0.8 |
SP-CHO Percentage | 56.7±0.4 | 56.5±0.4 | 47.8±1.0 | 45.8±0.9 | 44.8±1.3 | 46.3±1.3 |
SP-Protein Percentage | 16.3±0.2 | 15.9±0.2 | 18.5±0.5 | 19.5±0.5 | 20.2±0.8 | 20.5±0.7 |
SP-Fat Percentage | 27.4±0.3 | 28.1±0.4 | 32.8±1.0 | 34.1±0.8 | 33.7±0.9 | 32.4±1.1 |
HP-MJ per Day | 6.4±0.1 | 8.2±0.3 | 8.3±0.8 | 8.1±0.5 | 8.5±0.9 | 7.6±0.6 |
HP-CHO Percentage | 43.8±0.4 | 43.8±0.5 | 43.9±1.1 | 44.3±1.2 | 43.4±1.3 | 46.4±1.6 |
HP-Protein Percentage | 28.7±0.3 | 28.6±0.4 | 20.9±0.8 |
22.3±0.8 |
21.5±0.8 |
21.5±0.8 |
HP-Fat Percentage |
27.7±0.3 | 27.7±0.4 | 32.7±0.9 |
32.1±0.9 |
33.7±0.7 |
31.0±1.2 |
Other Findings
- There were similar dropouts in each group
- Energy intake did not differ between the diet groups during either the 12-week energy restriction, four-week energy balance or 12 -month follow-up phase
- After 12 weeks of energy restriction and four weeks of maintenance, decrease in weight was not affected by diet composition (SP, -9.1±0.7%; HP, -8.7±0.7%; P=0.44)
- At Week 68, there was net weight loss (standard protein, -2.9±3.6%; high-protein, -4.1±5.8%; P<0.01), due entirely to fat loss with no diet effect
- Both diets significantly increased HDL concentrations (P<0.001) and decreased fasting insulin, insulin resistance, sICAM-1 and CRP levels (P<0.05)
- Protein intake was significantly greater in high-protein during the initial 16 weeks (P<0.001), but decreased in high-protein and increased in standard-protein during 52-week follow-up, with no difference between groups at Week 68, indicating poor long-term dietary adherence behavior to both dietary patterns.
Author Conclusion:
- In summary, our findings indicate that in obese, hyperinsulinemic subjects, over a 68-week period, prescribing a low-fat, high-protein diet offers no greater advantages or disadvantages for weight loss, markers of CVD and dietary adherence, compared to a conventional standard protein diet
- However, due to poor dietary compliance, no conclusions can be made in relation to the direct long-term metabolic effects of a high-protein diet.
Funding Source:
Government: | national health and medical research council of australia | ||
Industry: |
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Reviewer Comments:
Dietary compliance assessed through urinalysis.
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? | 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? | 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)? | 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? | 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 | |