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DM: Protein (2007)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare the effects of two isocaloric diets, one high and one low in dietary protein (30% and 15% of energy respectively) on weight loss, resting energy expenditure (REE), respiratory quotient (RQ), and thermic effect of food (TEF) in subjects with type 2 diabetes after energy restriction and subsequent weight maintenance.
Inclusion Criteria:
Type 2 diabetes
Exclusion Criteria:
  • Proteinuria
  • History of liver, unstable cardiovascular, respiratory, or gastrointestinal disease, or a malignancy. 
Description of Study Protocol:

Recruitment

Public advertisement

 Design

Comparison, by diet (high protein or HP vs lower protein or LP) of weight loss, REE, RQ, and TEF at 0 and 8 weeks (weight loss period) and after a further 4 weeks (weight stable period) in individuals with type 2 diabetes.

Blinding used (if applicable)

None described 

Intervention (if applicable)

  • High protein diet: 30% energy from protein (~110 g/d), 40% from carbohydrate, and matched for fatty acid profile (8% saturated, 12% mono, 5% poly)
  • Lower protein diet: 15% energy from protein (~60 g/d), 55% from carbohydrate, and matched for fatty acid profile (8% saturated, 12% mono, 5% poly)
  •  First eight weeks (weight loss period) kcal were restricted to 1600 (30% restriction in energy); during the last 4 weeks, caloric intake was increased by 30%
  • Foods were eaten on an outpatient basis, with fixed menu plans, and with subjects receiving preweighed key foods (about 60% of energy intake)
  • Meeting every 2 weeks with research dietitian for detailed dietary instruction and assessment

Statistical Analysis

  •  Repeated measures ANOVA (to assess the effects of energy restriction and weight maintenance, with time as the within-subject factor and diet and gender as the between-subject factors).
  • Pearson correlation analysis (to determine the relationship between change in REE and TEF with the other variables).
  • no power calculations
Data Collection Summary:

Timing of Measurements

 Baseline (0), 8, and 12 weeks

Dependent Variables

  • body weight (light clothing): electronic scale
  • Body composition:whole-body dual X-ray absorptiometry (DEXA) (Norland densiometer XR36)
  • REE: indirect calorimetry with ventilated hood and Deltratrac metabolic monitor
  • RQ: indirect calorimetry as above
  • Postprandial RQ: after a ~600 kcal test meal (representative of HP/LP diets), indirect calorimetry as above every 20 min for 2 hr
  • TEF: calculated from fasting and postprandial REE values

Independent Variables

  • High protein diet: 30% energy from protein (~110 g/d), 40% from carbohydrate, and matched for fatty acid profile (8% saturated, 12% mono, 5% poly)
  • Lower protein diet: 15% energy from protein (~60 g/d), 55% from carbohydrate, and matched for fatty acid profile (8% saturated, 12% mono, 5% poly)
  •  First eight weeks (weight loss period) kcal were restricted to 1600 (30% restriction in energy); during the last 4 weeks, caloric intake was increased by 30%
  • Foods were eaten on an outpatient basis, with fixed menu plans, and with subjects receiving preweighed key foods (about 60% of energy intake)
  • Meeting every 2 weeks with research dietitian for detailed dietary instruction and assessment
  • Food records: 3 consecutive days (2 weekdays, 1 weekend day) every 2 weeks: Diet One nutritional software, Xyris Software
  • Urea/creatinine ratio: 24-h urine, weeks 0,8,12
  • medications (subjects on antihypertensive or lipid-lowering medication were asked to maintain their same dosage throughout the study)
  • physical activity (subjects were asked to maintain usual physical activity): 24-h activity recalls
  • alcohol (subjects were asked to refrain from drinking alcohol during study

Control Variables

  • type 2 diabetes
  • age
  • gender
    • Description of Actual Data Sample:

    Initial N: 32

    Attrition (final N): 26 (15 women, 11 men), 19% dropout rate.  4 withdrew during course of study, 2 subjects were not included in the analysis, 1 for non-compliance, 1 for lost data.

    Age: HP (15 subjects): 62.1±2.2 yrs; LP (11 subjects): 64.2±3.3 yrs

    Ethnicity: caucasian

    Other relevant demographics: none provided

    Anthropometrics: Baseline measurements assessed using two-way ANOVA (diet and gender as fixed factors); no indication of significant differences between groups before intervention (see table)

    Variables

    HP mean±SEM

    LP mean±SEM
    Weight (kg) 94.5±3.9 90.7±5.0
    BMI 33.9±1.2 32.6±1.4
    Waist circumference (cm) 110.8±3.0 107.8±3.8
    Body fat (%) 42.2±2.2 37.8±2.0
    Total body fat mass (kg) 40.0±2.8 34.4±2.8
    Total body lean mass (kg) 51.5±2.8 53.4±3.4
     

    Location: University of Adelaide, South Australia

     

    Summary of Results:

     Other Findings

    •  Mean weight loss for both diets was 4.6±0.5 kg (p<0.001), of which 4.5±0.4 kg was fat (p<0.001), with no effect of diet. 
    • At both weeks 0 and 12, TEF was greater after the HP than after the LP meal (0.064 vs 0.050 kcal/kcal energy consumed/2 hr, p=0.003). 
    •  REE and TEF were significantly reduced with each of the diets, with the decrease not related to diet composition
    • There was no significant difference  in postprandial RQ from week 0 to week 12 in either group. 
    • Dietary compliance was indicated by a significantly higher urea/creatinine ratio during the HP diet compared to the LP diet, and by percentages of macronutrients (from food records) at the end of 8 and 12 weeks (HP = 28% protein, 42% carbohydrate, 28% fat; LP = 16% protein, ~54% carbohydrate, and 26% fat). 
    • 24-h activity recalls indicated no significant differences for the previous day's activity level at week 0 vs 12.
    Author Conclusion:

    In patients with type 2 diabetes, a low-fat diet with an increased protein-to-carbohydrate ratio does not significantly increase weight loss or blunt the fall in REE.  The TEF was greatest after HP meals, and the fall in TEF after weight loss was less for women on the HP than on the LP diet.

    Funding Source:
    Industry:
    Meadow Lea Foods
    Food Company:
    Reviewer Comments:
    • 19% dropout rate - more dropouts in low protein diet group
    • Because of the study design, there is no way to determine if "high protein" or "low carbohydrate" produced the results
    • The study may be underpowered (no power calculations provided)
    • Study wasn't specifically powered to determine gender-by-diet interactions)

    Particular strengths of this study include

    • the multivariate statistical analysis
    • Subjects matched for fasting plasma glucose, BMI, age, gender, and medication
    • the study design, which measures subjects at the end of weight loss, AND after four weeks of stabilization at the lower weight
    • acknowledging control variables (even though most were not discussed in the results section, and smoking was not discussed at all). 
    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? ???
      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? ???
    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? ???
      4.1. Were follow-up methods described and the same for all groups? ???
      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? ???
      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.) 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? 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? 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