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DM: Weight Management (2001)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To determine the optimal diet for improving glucose and lipid profiles in obese patients with type 2 diabetes during moderate energy restriction.

Inclusion Criteria:

Free-living adult, Australian, obese individuals with type 2 diabetes.

Exclusion Criteria:

Subjects taking medications that would affect lipid metabolism.

Description of Study Protocol:

Recruitment: Recruited by public advertisement.

Design:

Randomized Controlled Trial.

Blinding Used (if applicable):

Not used.

Intervention:

Subjects randomized to 1 of 3 study diets for 12 weeks. The diets were designed to impose a 30% energy restriction, all at 1600 kcals. 

Statistical Analysis:

Data are means + SEM. Total areas under the glucose curves above baseline were calculated geometrically. Significance was determined with repeated-measures general linear model with and without covariates. Significance was set at P < 0.05.

 

 

Data Collection Summary:

Timing of Measurements:

  • Subjects were seen every 2 weeks by the same dietitian who provided dietary education and key foods.
  • Subjects were seen at the nutrition clinic for 2 consecutive days at: 0 (baseline), 1, 4, 8, and 12 weeks. Venous blood samples were conducted at these visits after a 12hr fast for serum lipids and weight & blood pressure were also measured at these visits. 
  • Fasting blood samples were taken at baseline, week 1, and week 12 to evaluate glycemic control except for HbA1C which was measured at baseline and week 12.
  • Waist circumference was measured before and after dietary intervention.
  • At weeks 0, 1, and 12, subjects underwent a 3-h oral glucose tolerance test.

Dependent Variables:

  • fasting plasma glucose
  • fasting plasma insulin
  • weight
  • blood pressure
  • serum lipids
  • Area under the OGTT curve

    Independent Variables:

  • Time (weeks)

  • Subjects were placed on one of the three following 30% energy restricted (1600 kcals) diets:

  • High SFA diet: 32% fat, 52% carbohydrate, 17% SFA, 10% MUFA, 2% PUFA.
  • High MUFA diet: 32% fat, 50% carbohydrate, 7% SFA, 15% MUFA, 9% PUFA.
  • High carbohydrate diet: 10% fat, 73% carbohydrate, 3.5% SFA, 3% MUFA, 2% PUFA.

  • Subjects were given detailed instructions for following the diet and for recording dietary intake at baseline

  • Subjects were asked to refrain from drinking alcohol and to maintain their usual physical activity patterns throughout the study.

  • Subjects were provided key foods to eat at home to modify fat intake: high fiber wheat bran breakfast cereal and low fat frozen meals. Specific foods for each experimental diet were also provided:

    • High carbohydrate diet: skim milk, raisins, and low-fat biscuits
    • High MUFA diet: skim milk, almonds, and biscuits made with unsaturated fat.
    • High SFA diet: whole milk, chocolate, short bread biscuits

     Control Variables

    • Description of Actual Data Sample:

    Initial N: 42 subjects

    Attrition (final N): 35 subjects (8 men, 27 women). 7 subjects withdrew during the course of the study due to work commitments or illnesses unrelated to diabetes. Dropout rate was 17%.

    Age: 54 - 62 yrs

    Ethnicity: Caucasian

    Other Relevant Demographics: 27 females, 8 males, 18 had type 2 diabetes controlled by diet alone, 17 were taking oral hypoglycemic meds to control their type 2 diabetes.

    Anthropometrics: Subjects were matched on the basis of age, sex, BMI, and use and type of diabetes medication. Each group had a similar amount of subjects taking metformin or sulfonylureas or using diet therapy alone. No subjects were taking medications known to affect lipid metabolism. The groups were generally similar, however; the high carbohydrate and high MUFA groups were sigificantly different than the high SFA group for total cholesterol and LDL at baseline ( p < 0.01).

    Location: Australia

     

     

    Summary of Results:

    Baseline LDL and total cholesterol levels were significantly lower in the high-SFA group compared to the high-carbohydrate and high-MUFA groups (p<0.05).

    HDL was significantly lower in the high-MUFA group compared to the high-SFA group (p=0.01).

      High-CHO High-MUFA High-SFA
    n (F/M) 12 (9/3)  13 (11/2) 10 (7/3)
    Age, yr 57.5±3.4 58.7±2.5 58.9±3.0
    LDL (mmol/l) 3.91+ 0.23 3.99+ 0.22 3.16+ 0.19
    HDL (mmol/l) 0.96+ 0.06 0.82+ 0.06 1.06+ 0.06
    BMI (kg/m2) 32.6±1.35 33.6±0.87 33.3±1.18
    HbA1c,% 8.51±0.41 7.75±0.49 7.46±0.23

    Weight loss was not significantly different between groups, but weight loss was significant at each time point (p<0.01) with subjects losing an average of 6.6 + 0.9kg after twelve weeks.

    Parameter Decrease at week 12 (%) P value
    waist circumference 7 in men, 6 in women <0.001
    fasting plasma glucose (FPG) 14 < 0.001
    fasting insulin 27 <0.001
    HbA1c 14 < 0.001
    systolic blood pressure 10 < 0.001
    diastolic blood pressure 7 < 0.001
    glucose response area 17 < 0.01

    Dietary composition of stidy diets derived from subjects' 3-day food records

      High-CHO High-MUFA High-SFA
    n (F/M) 12 (9/3)  13 (11/2) 10 (7/3)
    Energy (kcals/day) 1,541 + 41 1,596 + 34 1,613 + 61 
    Carbohydrate ( % of energy) 72.6 + 0.7 49.5 + 0.4 52.2 + 0.6
    Total fat ( % of energy) 9.9 + 0.4 32.2 + 0.4 31.4 + 0.6
    SFA ( % energy) 3.5 + 0.2 6.8 + 0.1 16.6 + 0.4
    MUFA (% energy) 3.0 + 0.1 14.8 + 0.2 9.9 + 0.2
    Polyunsaturated fat (% energy) 2.1 + 0.1 9.0 + 0.1 2.1 + 0.1
    Protein ( % energy) 16.8 + 0.5 18.2 + 0.3 16.6 + 0.4
    Fiber (g/day) 38.6 + 0.9 37.7 + 1.1 39.4 + 1.2
    Cholesterol (milligram/megajoule) 11.5 + 0.9 11.1 + 0.5 21.5 + 0.7

    Other Findings:

    Diet LDL-C
    • High-CHO (-10%)
    • High-MUFA (-17%)
    • High-SFA (0%)

    Diet composition had a significant effect on diet (p<0.001)

    Author Conclusion:

    Energy restriction and weight loss improve glycemic control and blood pressure independent of diet composition.  However, both low-fat, high-carbohydrate diets and moderate-fat high MUFA diets improved the CHD risk profile. This suggests that reducing the level of SFA in energy-restricted diets for type 2 diabetes may require more emphasis than total fat restriction.

     

    Funding Source:
    Government: Commonwealth Science Industrial Research Org (Austrialia)
    University/Hospital: University of Adelaide
    Reviewer Comments:

    Good compliance to the study given it was an outpatient study and not conducted in a metabolic ward. Compliance likely due to 60% of food provided by researchers.

    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? ???
      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.) 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? ???
      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? No
      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)? No
      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? No
      10.2. Was the study free from apparent conflict of interest? Yes