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DF: Diabetes (2008)

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

To examine the impact of dietary fibers, glycemic load and glycemic index on adiponectin concentration in men with type 2 diabetes mellitus.

Inclusion Criteria:
  • Male health professionals
  • Aged 40 to 75 years
  • Confirmed type 2 diabetes, as per the National Diabetes Group criteria.
Exclusion Criteria:
  • Evidence of
    • Fatal coronary heart disease
    • Non-fatal MI
    • CABG
    • Percutaneous transluminal coronary angioplasty
    • Fatal stroke
    • Non-fatal stroke at blood draw.
Description of Study Protocol:

Recruitment

Male health professionals recruited to the Health Professionals' Follow-Up Study, nationally.

Design

  • Cross-sectional analysis of 780 type-2 diabetic men enrolled in the Health Professionals' Follow-Up Study, that meet inclusion criteria
  • Detailed dietary information regarding intake in the previous year was collected using semi-quantitative FFQ in 1986, 1990 and 1994. Cumulative average of the three FFQ was used.
  • For the purposes of this study, data was collected on carbohydrate intake, fat intake, glycemic index, glycemic load and fiber
  • Carbohydrate intake and fat intake were expressed as nutrient density
  • Glycemic index, glycemic load and fiber were energy-adjusted, using residual method
  • Blood samples were collected between 1993 and 1994 and analyzed for adiponectin
  • Anthropometric and lifestyle questionnaires were administered once in 1986
  • Physical activity was expressed as metabolic equivalents, based on self-report.

Statistical Analysis

  • Linear regression (dietary intake and adiponectin levels)
  • Quintiles (dietary variables)
  • Adjustment for confounding variables
  • Test for effect modifications (BMI, physical activity, alcohol consumption).
Data Collection Summary:

Timing of Measurements

  • Food Frequency Questionnaire: Three times (1986, 1990 and 1994)
  • Blood analysis: Once between 1993 and 1994
  • Anthropometric and lifestyle questionnaires: Once (1986).

Dependent Variables

Serum adiponectin level.

Independent Variables

  • Cereal fiber intake
  • Dietary glycemic load
  • Dietary glycemic index.

Control Variables

  • Age
  • BMI
  • Smoking
  • Alcohol consumption
  • Physical activity
  • Hypertension
  • Hypercholesterol.
Description of Actual Data Sample:
  • Initial N: 780 (780 males, zero females)
  • Attrition (final N): Not applicable.

Age

  • Q1: 53±8 years
  • Q2: 55±8 years
  • Q3: 55±9 years
  • Q4: 57±7 years
  • Q5: 58±8 years.

Ethnicity

Not described.

Other Relevant Demographics

  • Highest quintile of adiponectin were or had:
    • Older
    • Leaner
    • More likely to consume alcohol
    • More physically active
    • More use of insulin
    • Less hypertension
    • Less hypercholesterolemia
    • Less family history of MI.

Anthropometrics

No significant differences between quintiles.

Location

National, Health Professionals' Follow-Up Study.

Summary of Results:
  • Carbohydrate: No significant effect on plasma adiponectin levels
  • Glycemic index
    • Decreasing adiponectin with increasing intake of high-glycemic index foods (P=0.005; multivariate modeling plus BMI)
    • Adiponectin 13% lower in highest quintile of high-glycemic index food intake.
  • Glycemic load
    • Decreasing adiponectin with increasing intake of high-glycemic load foods (P=0.004; multivariate modeling plus BMI)
    • Adiponectin 18% lower in highest quintile of high-glycemic load food intake.
  • Total fiber: No significant effect on plasma adiponectin levels
  • Cereal fiber
    • Decreased adiponectin with increased intake of cereal fibers (P=0.043; multivariate modeling plus BMI)
    • Adiponectin 19% lower in highest quintile of high-cereal fiber intake
      • Attenuated with adjustment for magnesium.
  • Vegetable fiber: No significant effect on plasma adiponectin levels
  • Fruit fiber: No significant effect on plasma adiponectin levels
  • Magnesium: Increased adiponectin levels with increased magnesium intake (P=0.011, multivaritae modeling plus BMI)
  • Other results: Highest intake of cereal fiber and lowest glycemic load had highest adiponectin levels (P=0.0097).
Author Conclusion:

Lower dietary glycemic index and glycemic load are associated with higher plasma adiponectin levels independent of fiber intake, indicating a potential benefit in type-2 diabetics; whereas cereal intake is associated with lower plasma adiponectin levels and may be less beneficial to individuals with type-2 diabetes.

Funding Source:
Government: NIH
Reviewer Comments:

Data based on an average of three FFQ.

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.) N/A
  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? Yes
  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.) Yes
  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? N/A
  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? N/A
  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? No
  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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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)? 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