DF: Diabetes (2008)

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

To examine the effects of fiber, in the form of guar powder and pectin, on blood glucose concentrations in individuals with diabetes.

Inclusion Criteria:
  • Non-insulin-dependent diabetic
  • Insulin-dependent diabetic.
Exclusion Criteria:

Not described.

Description of Study Protocol:
  • Recruitment: Not described
  • Design: Randomized crossover study of 11 diabetic patients to test meal (breakfast) with or without fiber-supplemented bread (16g guar gum, 10g pectin). A one- to two-week washout period occurred between meals.
  • Blinding used: N/A.


  • Subjects were randomly assigned to consume a test breakfast either with or without fiber supplementation
  • The intervention meal included fiber-supplemented bread (16g guar gum, 10g pectin) and the control meal did not
  • Individuals on oral hypoglycemic agents did not take their medication on test days
  • Insulin-requiring individuals did take their insulin
  • Following a 14-hour fast, subjects consumed the assigned breakfast in 15 to 20 minutes
  • Serum glucose and insulin levels were collected at zero, 15, 30, 45, 60, 90, 120, 150 and 180 minutes post-prandial
  • Subjects underwent a one- to two-week washout period prior to crossing-over to the other test group.

Statistical Analysis

  • Means with standard error
  • Student’s T-test (paired data).
Data Collection Summary:

Timing of Measurements

The following data was collected at 0, 15, 30, 45, 60, 90, 120, 150, 180 minutes post-prandial of the two test meals:

  • Serum glucose
  • Serum insulin.

Dependent Variables

  • Serum glucose
  • Serum insulin.

Independent Variables

Fiber intake.

Description of Actual Data Sample:
  • Initial N: 11 (six males, five females); eight insulin independent (four male, four female); three insulin-requiring (two males, one female)
  • Attrition: Not described.


  • Insulin independent: 58±5 years
  • Insulin-requiring: 21 years.


Not described.


  • Insulin independent: 120%±11% DBW
  • Insulin-requiring: 105%±3% DBW.


General Hospital, Southampton and Radcliffe Infirmary; Oxford, England.

Summary of Results:

Serum Glucose; Insulin Independent Diabetes (N=8)

  • Significantly lower following fiber-containing meal at:
    • 30 minutes (2.61±0.61mmol per L, P<0.01)
    • 45 minutes (3.45±0.95mmol per L, P<0.01)
    • 60 minutes (3.56±0.95mmol per L, P<0.01)
    • 90 minutes (3.06±0.95mmol per L, P<0.02).

Serum Glucose; Insulin-Requiring Diabetes (N=3)

Significantly lower following fiber-containing meal (data not reported).

Serum Insulin; Insulin Independent Diabetes (N=8)

  • Significantly lower following fiber-containing meal at:
    • 30 minutes (11±4 milliunits per L, P<0.05)
    • 45 minutes (19±6 milliunits per L, P<0.02)
    • 60 minutes (22±5 milliunits per L, P<0.01)
    • 90 minutes (24±5 milliunits per L, P<0.002)
    • 120 minutes (19±4 milliunits per L, P<0.01).
Author Conclusion:

Fiber-enriched diets, including guar gum and pectin, significantly decrease blood glucose concentrations and serum-insulin in individuals with type 1 and type 2 diabetes.

Funding Source:
Government: US Public Health Service, Swiss National Research Foundation
Foundation associated with industry:
Reviewer Comments:
  • Small sample size, which is even smaller when broken down by type of DM
  • No description of inclusion or exclusion criteria
  • Limited presentation of demographic data
  • Large difference in age between insulin and non-insulin-requiring groups
  • No power calculation presented
  • No description of diet composition
  • No data collected or presented on baseline (pre-meal) serum glucose or insulin levels
  • No description of randomization scheme
  • No description of diet tolerance.
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? 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.) 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? No
  4.1. Were follow-up methods described and the same for all groups? No
  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? No
  4.4. Were reasons for withdrawals similar across groups? No
  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? No
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? No
  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? 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? No
  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? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? No
  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)? No
  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? Yes
  10.2. Was the study free from apparent conflict of interest? Yes