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HTN: Protein (2007)

Citation:
 
Study Design:
Class:
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Quality Rating:
Research Purpose:
The aim of the study was to compare the effects of two isoenergetic, energy-restricted diets with either a high or standard content of dietary protein (27% or 16% of energy, respectively, as protein) on body composition, glucose and insulin homeostasis, lipid concentrations, bone turnover and blood pressure in obese subjects with hyperinsulinemia.
Inclusion Criteria:
  • Age 20-65 years
  • Fasting serum insulin concentration over 12mU per L
  • Body mass index (BMI) of 27-43kg per m2.
Exclusion Criteria:
  • Diabetes mellitus
  • Proteinuria
  • History of liver, unstable cardiovascular, respiratory or gastrointestinal disease or of malignancy.
Description of Study Protocol:

Recruitment

Public advertisement.

Design

  • The study was conducted on an outpatient basis over 16 weeks
  • Subjects were matched on the basis of fasting concentrations at screening, BMI, age and sex
  • Subjects from each group were then randomly assigned to either the HP or SP diet group
  • Screening occurred four to six weeks before the study
  • Both groups underwent 12 weeks of energy restriction (approximately 30% restriction of total energy or 6.4MJ on average), followed by four weeks of energy balance with the same micronutrient composition. 

Intervention

  • The high-protein contained 30% of energy as protein (approximately 110g per day), 40% as carbohydrate and 30% as fat or contained a standard amount of protein [15% of energy as protein (approximately 60g per day), 55% as carbohydrate and 30% as fat]
  • The fatty acid profiles were matched (8% of energy as saturated, 12% as monounsaturated and 5% as polyunsaturated fatty acids)
  • The diets were prescriptive fixed-menu plans and subjects were supplied with key foods that made up 60% of their energy intake.  

Statistical Analysis

  • Baseline measurements were assessed using two-factor analysis of variance with diet and sex as the fixed factors
  • Dietary intake was assessed using the unpaired T-test
  • The effect of intervention was assessed using repeated-measures analysis of variance (with covariates of baseline weight, total fat mass, and total lean mass in specific analyses) with variables measured at Weeks Zero, Four, Eight, 12 and 16
  • Diet and sex were the between-subject factors
  • The incremental area under the glucose and insulin response curves during the three-hour meal tolerance tests was calculated geometrically by using the trapezoidal rule
  • The homeostasis model assessemnt (HOMA) for insluin resistance was calculated as (fasting insulin x fasting glucose/22.5)
  • Significance was set at 0.05 (without Bonferroni correction)
  • The T-tests were two-sided.
Data Collection Summary:

Timing of Measurements

Baseline and at four, eight, 12 and 16 weeks.

Dependent Variables

  • Blood pressure
  • Body weight
  • Body composition measured by DEXA
  • Plasma glucose levels
  • Serum insulin levels
  • Plasma fatty acid concentrations.

Independent Variables

  • High-protein
  • Standard protein diet.

Control Variables

  • Dietary compliance was assessed using the ration of urinary urea to creatinine
  • Markers of bone turnover and calcium excretion.
Description of Actual Data Sample:
  • Initial N: 66
  • Attrition (final N): 57 (14 men, 43 women)
  • Age: 20 to 65 years
  • Ethnicity: Not specified
  • Location: Adelaide, Australia.

 

Summary of Results:

Variables

Standard Protein Diet

     High-Protein Diet
  Men (N=7)     Women (N=21) Men (N=7)     Women (N=21)

Body Weight (kg)2,3

    

 

 
  Week Zero 108.8±5.2     88.1±2.3 107.8± 5.9 89.1±2.2
  Week Four 103.5±4.8 84.7±2.2 102.7±5.2 86.4±2.2
  Week Eight 100.7±4.2 82.7±7±2.3 98.5±4.9 84.4±2.2
  Week 12  99.2±4.1 81.1±2.3 96.3±4.3 82.5±2.3 
  Week 16  99.2±1.7 80.7±2.3 96.3±4.3 82.5±2.3
  Change -9.6±1.7 -7.4±0.5 -11.4±2.1 -6.6±0.5
Total fat mass (kg)2,3        
  Week Zero  38.2±3.3 42.7±2.0 37.8±3.3 43.2±1.3
  Week 16  30.6±2.9 35.6±1.9 28.8±1 2.0 36.6±1.4
  Change -7.6 3.1 -7.1 2.0 -9.0 2.7 -6.6 1.4
Abdominal fat (kg)2,3        
  Week Zero  15.7±1.6  15.6±0.6  15.6±1.4 15.4±0.5
  Week 16  12.2±1.3  12.7±0.7  11.1±0.8 12.5±0.5
  Change  -3.5±0.7  -2.6±0.2  -4.5±1.0 -2.8±0.3
Total lean mass (kg)2,3        
  Week Zero 67.0±2.1 42.4±0.9 66.1±3.1 42.5±1.1
  Week 16 65.1±2.1 40.9±0.9 63.6±2.4 42.4±1.2
  Change -1.9±2.1 -1.5±0.3 -2.5±2.8 -0.1±0.3
Total cholesterol        

 Week Zero

 5.25±0.35  5.70±0.18 6.11±0.41 5.36±0.24
 Week Four 4.39±0.29  5.34±0.29 4.66±0.20 4.84±0.23
 Week Eight 4.59±0.35  5.26±0.20 4.70±0.24 4.91±0.20
 Week 12 4.55±0.38  5.31±0.25 4.69±0.26 4.92±0.22
 Week 16 4.83±0.37  5.51±0.21 5.22±0.31 5.12±0.23
 Change -0.42±0.10 -0.19±0.16 -0.89±0.33 -0.24±0.12
LDL cholesterol        
 Week Zero 3.51±0.32 3.84±0.18  4.11±0.33  3.65±0.21
 Week Four 2.89±0.28 3.59±0.21  3.10±0.15  3.32±0.21
 Week Eight 2.93±0.34 3.47±0.20  3.09±0.16  3.26±0.17
 Week 12 2.90±0.35 3.53±0.24  3.05±0.18  3.76±0.20
 Week 16 3.14±0.33 3.66±0.21  3.51±0.20  3.32±0.20
 Change 0.38±0.15 -0.17±0.15 -0.17±0.31  0.14±0.11
HDL cholesterol        
 Week Zero 0.89±0.06 1.00±0.06 0.90±0.06 1.00±0.05
 Week Four 0.89±0.07 0.97±0.05 0.93±0.04 0.93±0.04
 Week Eight 0.90±0.07 0.96±0.04 0.83±0.11 0.97±0.04
 Week 12 0.92±0.06 1.01±0.04 1.03±0.08 1.00±0.04
 Week 16 0.97±0.06 1.05±0.04 1.03±0.05 1.00±0.04
 Change 0.08±0.02 0.04±0.04 0.13±0.04 0.03±0.3
Triacylglycerol        
 Week Zero 1.84±0.30 1.89±0.12 2.39±0.33 1.71±0.13
 Week Four 1.33±0.14 1.69±0.10 1.39±0.15 1.37±0.11
 Week Eight 1.52±0.25 1.66±0.12 1.56±0.28 1.43±0.12
 Week 12 1.62±0.25 1.67±0.13 1.31±0.18 1.34±0.11
 Week 16 1.58±0.28 1.74±0.12 1.71±0.23 1.34±0.12
Change -0.27±0.16 -0.15±0.11 -0.68±0.21 -0.37±0.08

Other Findings

Variables

SP Diet (N=29)

 HP Diet (N=28)
Fasting glucose (mmol/L)      
  Week Zero

5.3±0.1      

 5.4 ±0.1
  Week Four 5.3±0.1 5.3 ± 0.1
  Week Eight 5.2±0.1 5.6±0.1
  Week 12 5.2±0.1 5.4±0.1
  Week 16   5.2±0.1 5.5±0.1
  Change -0.1±0.08 -0.16 ±0.1
Glucose AUC (mmol·180 min/L)2,3

 

  
  Week Zero 1,300±49 1,202±32
  Week 16 1,265±48 1,099±40
Fasting insulin (mU/L)2    
  Week Zero 17.7±2.4 17.5±1.2
  Week Four 12.5±1.3 12.6±1.1
  Week Eight 10.7±0.9 13.5±1.4
  Week 12 10.4±0.6 10.5±0.7
  Week 16 11.5 ±0.9 11.9±1.1
  Change 6.2±2.0 -5.6±0.9
Insulin (mU·180 min/L)2,3    
  Week Zero 9,108±1094 7,935±726
  Week 16 8,719 ± 718 5,922±533
  Change 389±300 2,013±337
Fatty acids2    
  Week Zero 0.4±0.03 0.4±0.03
  Week Four 0.4±0.02 0.4±0.02
  Week Eight 0.3±0.03 0.3±0.02
  Week 12 0.3±0.02 0.3±0.03
  Week 16 0.3±0.02 0.3±0.03
   Change -0.10±0.03  -0.11±0.02 

  • Systolic blood pressure decreased from 130±1.9mm Hg at Week Zero to 126±1.8mm Hg at Week 12 (P=0.022)
  • But by Week 16, systolic blood pressure (126±2.3mm Hg) did not differ from that at Week Zero
  • At both Weeks 12 and 16, diastolic blood pressure (72±1.3 and 72±1.4mm Hg, respectively) was significantly (P<0.04) lower than that at Week Zero (74±1.4mm Hg)
  • There was no effect of either diet or sex on systolic or diastolic blood pressure. 
Author Conclusion:
Replacing carbohydrate with protein from meat, poultry and diary foods has beneficial metabolic effects and no adverse effects on markers of bone turnover or calcium excretion. 
Funding Source:
Government: National Health and Research Grant
Industry:
Dairy Research and Development Grant
Food Company:
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? 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")? Yes
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? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? Yes
  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.) Yes
  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? ???
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? ???
  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)? ???
  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? ???
  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? No
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