DF: Diabetes (2008)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To verify the effect of soluble (viscous) fiber, and the lack of effect of insoluble fiber, in the modulation of postprandial glycemia in individuals with type 2 diabetes.
Inclusion Criteria:
type 2 diabetes
Exclusion Criteria:

none given

Description of Study Protocol:


none given


Comparison of plasma glucose and insulin in 10 adults with type 2 diabetes for three hours after eating a meal low in fiber (6.7 g) vs either a meal high in soluble fiber (32.9 g fiber, 14 g soluble fiber) or a meal high in insoluble fiber (33.6 g fiber, 27.2 g insoluble fiber).

Blinding used (if applicable)


Intervention (if applicable)

Three lunch meals were designed to be similar in calories (870-880), carbohydrate (~45% of calories), protein (~18%), and fat (~37%), but different in fiber: low fiber (LF); high soluble fiber (HSF); high insoluble fiber (HIF).  All dietary fiber was from foods rather than supplements (e.g.: white pasta for the LF; beans and fresh vegetables for the HSF; bran-enriched pasta and whole wheat bread for the HIF). Subjects ate the meals in randomized order, with 2 weeks washout between meals. Subjects were not treated with any drug "during the experiment"

Dietary fiber (g) 6.7 32.9 33.6
Soluble fiber (g) 2.0 14.3 6.4
Insoluble fiber (g) 4.7 18.6 27.2

 Statistical Analysis

 paired t-test (two-tailed) to compare results

Data Collection Summary:

Timing of Measurements

 Baseline and 15, 30, 45, 60, 90, 120,and 180 minutes after baseline

Dependent Variables

  • Blood glucose (glucose oxidase method) 
  • Serum insulin (radioimmunoassay)

Independent Variables

  • Dietary (soluble and insoluble) fiber (determined in duplicate portions of the meals by a modification of the enzymatic gravimetric AOAC method)

Control Variables


Description of Actual Data Sample:

Initial N: 10 (4 women, 6 men)

Attrition (final N): none reported, 10

Age: Mean of 54 years (range, 34-67 yrs)

Ethnicity: not reported

Other relevant demographics: Mean duration of diabetes, 2.9 years (range 1.5 to 10)


  • Mean glysocylated hemoglobin: 8.2% (range 7.0-15)
  • Mean BMI: 26.8 kg/m2 (range21.2-36.5)

Location: Ospedale Forlanini, Rome, Italy

Summary of Results:



Low Fiber (LF) Meal n=10

Mean ± SEM

High Soluble Fiber (HSF) Meal n=10

Mean ± SEM

High Insoluble Fiber Meal (HIS) n=10

Mean ± SEM

Significant difference, HSF vs LF*

Blood gluocose (mg/dl) 30 min

186±14.2 141±9.2 180±10.7 p < 0.02

     60 min




p < 0.01

    120 min





Serum insulin (µU/ml)  30 min

26.5±5.9 25.3±4.5 30.4±4.2 ns
     60 min 30.0±7.3 25.0±4.1 34.4±5.8 p<0.05
    120 min 35.9±7.8 27.1±4.4 44.0±6.1 ns

 *LF and HIF meals resulted in almost identical glycemic responses

Other Findings


Author Conclusion:
  • The postprandial blood glucose and serum insulin responses to the LF and HIF test meals were similar, and the HSF meal produced significantly lower glucose and insulin responses compared to either LF or HIF meals.
  • Using HSF diets (fruits, vegetables, beans), prevent excessive insoluble fiber and may improve patient compliance.


Funding Source:
Reviewer Comments:
  • This study chemically analyzed total, soluble, and insoluble dietary fiber in the test meals rather than just calculating fiber from food composition tables
  • This report lacks a description of some of the essential components of research design: description of recruitment, inclusion and exclusion criteria, description of randomization
  • The meals in this study had similar macronutrient % of energy, thus macronutrient differences were NOT confounders.
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? No
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  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? 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? Yes
  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.) 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? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  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? N/A
  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? N/A
  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)? N/A
  8.6. Was clinical significance as well as statistical significance reported? N/A
  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? ???
  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? ???
  10.2. Was the study free from apparent conflict of interest? Yes