EAL

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:

Dairy Research and Development Grant

Commodity Group:

Reviewer Comments:

Dietary compliance assessed through urinalysis.

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?		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