DF: Diabetes (2008)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  1. To examine the effects of low- and high-fiber meals on glucose and insulin levels in type 2 diabetics
  2. To examine the effect of two types of high-fiber meals on glucose and insulin levels.
Inclusion Criteria:
  • Diet-controlled type 2 diabetes
  • Had been seen by an RD within the past 12 months.
Exclusion Criteria:

Not described.

Description of Study Protocol:
  • Recruitment: Not described
  • Design: Each of the five participants ate one of three breakfasts in random order over three weeks, with one week between test meals
  • Blinding used: Not described, but outcome was objective
  • Intervention
    • Three breakfast meals
    • Refined meal had 3 g of fiber; High in bran fiber meal had 17 g fiber; High in bran and fruit fiber had 18 g of fiber of which four were soluble fiber; meals ranged from 324 to 348 kcals; meals eaten under supervison; CHO content of meals was similar.

















Bran + Fruit





Statistical Analysis

  • Student's T-test
  • AUC (Glucose and xylose).
Data Collection Summary:

Timing of Measurements

  • Blood samples drawn at 10, 30, 90, 120 and 180 minutes for glucose, insulin, glycogen, growth hormone and xylose
  • Diet consumed during 20 minutes at laboratory
  • Questionnaire regarding after-effects of meals completed within 24 hours of meal consumption
  • 24-hour recall; reviewed with each participant prior to meal.

Dependent Variable

  • Glucose
  • Xylose
  • Insulin
  • Growth hormone
  • Glucagon.

Independent Variables

  • Fiber (control, bran or bran and fruit)
    • Quantity
    • Type.

Control Variables


Description of Actual Data Sample:
  • Initial N: Five (two males and three females)
  • Attrition (final N): Not described
  • Age: 50.2 years (range, 32 to 68 years)
  • Ethnicity: Not described.

Other Relevant Demographics

  • Diet-controlled type 2 diabetes, for a mean of 3.8 years
  • All participants had been seen by an RD within the past 12 months.


All five were "lean" (within 110% of desirable body weight).


Sunnybrook Medical Center; Toronto, Canada.

Summary of Results:

Effects of Dietary Fiber on Blood Glucose and Xylose





Bran and Fruit


AUC (mg)




Peak Serum Glucose (Percentage Rise Baseline)





AUC (mg)




* Refined vs. Bran (P<0.05)
** Refined vs. Bran and Fruit (P<0.01).

Other Findings

  • Bran
    • No difference in insulin values and growth factor
    • Decreased serum glucagon at 90 minutes (P<0.05).
  • Bran and Fruit
    • Glucose higher than refined diet at 120 minutes (P<0.05)
    • Rise from baseline lower than refined diet (P<0.01)
    • No effect on xylose, insulin or growth factor.
Author Conclusion:

Bran supplement produced and immediate improvement in parameters of glucose metabolism, potentially via altered glucose absorption or hormonal factors.

Funding Source:
University/Hospital: Sunnybrook Medical Center (Canada)
Reviewer Comments:
  • This is a study of five participants with methodological flaws
  • The findings are not generalizable
  • The participants were NIDDM within 110% of ideal body weight, which would not be the norm
  • There were several outcomes and timepoints reported and it wasn't clear what we would have expected to observe. For example, is 180 minutes the appropriate time to report these outcomes or is the outcome more relevant at 90 minutes?
  • The author also did not account for multiple comparisons.
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? No
2. Was the selection of study subjects/patients free from bias? No
  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? No
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  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? 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? No
  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%.) No
  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? 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? 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? 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? No
  6.6. Were extra or unplanned treatments described? No
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? No
  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? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? ???
  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)? No
  8.6. Was clinical significance as well as statistical significance reported? No
  8.7. If negative findings, was a power calculation reported to address type 2 error? No
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? No
  10.2. Was the study free from apparent conflict of interest? Yes