DF: Diabetes (2008)


Mahalko JR, Sandstead HH, Johnson LK, Inman LF, Milne DB, Warner RC, Haunz EA. Effect of consuming fiber from corn bran, soy hulls, or apple powder on glucose tolerance and plasma lipids in type II diabetes. Am J Clin Nutr. 1984 Jan; 39 (1): 25-34.

PubMed ID: 6318545
Study Design:
Randomized Controlled Trial
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To examine the effects of dietary fiber from three diferent sources (corn bran, soyhulls or apple powder) on glycemic control and plasma lipids in persons with type 2 diabetes.

Inclusion Criteria:

Type 2 diabetes.

Exclusion Criteria:

Not specified.

Description of Study Protocol:


  • Referred by private physicians
  • Response to an advertisement (not described).


  • Participants consumed seven slices of control (low-fiber) or bread supplemented with soy hulls, corn bran or dehydrated powdered apple, daily, but were told to maintain current eating habits and suggested to replace other high-CHO items with the bread
  • White bread was used as the control
  • Each subject was randomly rotated through each of the high-fiber bread diets and the control diet for a period of four weeks each (control, soy hulls, corn bran or dehydrated powdered apple).

Fiber Source

Crude Fiber

Apple Powder

3.8% wet weight

Corn Bran

19% wet weight

Soybean Hulls

38% wet weight

Two studies were conducted this way

  • Study A: 10 subjects consumed 26g of fiber incorporated into seven slices of bread
  • Study B: Eight subjects consumed 26g of fiber incorporated into seven slices of bread and an additional 26g from dietary sources. Participants were given suggestions on how to incorporate the fiber souces into other foods.

Data was collected in the same manner for both studies. The following was collected at baseline and every two weeks thereafter:

  • Three-day diet records
  • Post-prandial glucose tolerance test
  • Body weight
  • Fasting lipds
  • HgbA1C
  • 24-hour urinary glucose.

Blinding Used

Not described. 


Two studies were conducted where subjects consumed one of four test diets (control, soy hulls, corn bran or dehydrated powdered apple) for four weeks in random order until all subjects had consumed all diets.

  • Study A: 10 subjects consumed 26g of fiber incorporated into seven slices of bread
  • Study B: Eight subjects consumed 26g of fiber incorporated into seven slices of bread and an additional 26g from dietary sources
  • Participants were given suggestions on how to incorporate the fiber souces into other foods.

Statistical Analysis

  • Linear regression (change in body weight)
  • ANOVA (with correction for multiple comparisons)
  • P=0.
Data Collection Summary:

Timing of Measurements

The following was collected at baseline and every two weeks thereafter

  • Three-day diet records
  • Post-prandial glucose tolerance test
  • Body weight
  • Fasting lipids
  • HgbA1C
  • 24-hour urinary glucose.

Dependent Variables

  • Serum glucose
  • Urinary glucose
  • Serum lipids.

Independent Variables

  • Quantity of fiber consumed
  • Type of fiber consumed.

Control Variables

  • Absolute weight
  • Percent desirable weight
  • Percentage weight change from admission.
Description of Actual Data Sample:

Initial N

  • Study A: 10 subjects; five men and five women
  • Study B: 10 subjects; two men and six women.

Attrition (Final N)

  • Study A: 10 subjects; five men and five women
  • Study B: Eight subjects; two men and six women.


  • Study A: 65±5.9 years
  • Study B: 61.4±5.8 years.




  • Initial body weight
    • Study A: 71.3±12.6kg
    • Study B: 73.5±10.8kg.
  • Initial percentage of desirable body weight
    • Study A: 119.7%±24%
    • Study B: 123.8±22.1%.


Grand Forks Clinic, ND.

Summary of Results:

Fiber Tolerance

  • Subjects tolerated the 26 grams of fiber source
  • In the corn bran group, the additional 26 grams was not well-tolerated
    • Constipation and fecal impaction described
    • Two drop-outs were a result of intolerance.

Dietary Intake

  • There were no changes in protein or fat during the study period
  • Study A
    • Increase of 38g of CHO (P<0.0001) to 47% energy (P<0.05).
  • Study B
    • Increase in energy of 322Kcals (P<0.05)
    • Increase of 58g CHO (P<0.01).


Several subjects in Study B significantly increased body weight (range, 1.3kg to 4.5kg; P-value not provided).

Glucose Control

  • Soy hulls significantly improved glucose score (P<0.05) and glucose AUC, compared to admission (P<0.05)
  • Soy hulls significantly improved  glucose AUC compared to control in Study B only (P<0.05)
  • No effect of soy hulls or apple powder on HgbA1C or 24-hour urinary glucose
  • No effect of corn bran or apple powder on glucose
  • Improvement of HgbA1C, compared to control diet in Study B only (P<0.05).

Plasma Lipids

  • Soy hulls increased plasma HDL, compared to admission (P<0.05)
  • Corn bran decreased VLDL (P<0.05) and triglyceride levels (P<0.05) in Study B only
  • Apple powder increased LDL (P<0.05) and total cholesterol (P<0.05).
Author Conclusion:
  • Dietary fiber supplementation in the form of soy hulls may have a beneficial effect on serum glucose control
  • Daily corn bran supplementation has beneficial effects on serum lipids but is poorly tolerated, limiting generalized applicability.
Funding Source:
Government: USDA
University/Hospital: Grand Forks Human Nutrition Center,
Reviewer Comments:
  • This manuscript reports results from two studies
  • Three subjects were in both studies
  • Details about the methods are lacking
  • Demographics on two drop-outs not provided.
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? No
  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) No
  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? 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? No
  4.4. Were reasons for withdrawals similar across groups? ???
  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? 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? 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)? No
  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? 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? 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