DM: Fiber (2014)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To compare three sets of dietary guidelines for the treatment of 2 diabetes in free-living individuals and to observe the effects on metabolic control over an 18-month period.
Inclusion Criteria:
No major illness other than type 2 diabetes
Exclusion Criteria:
  • taking insulin
Description of Study Protocol:


From the Dunedin Hospital Diabetes Clinic and through local general practitioners


Comparison of nutrient intakes, weight, blood lipids, and glycemic control at baseline and at regular intervals during 18 months while subjects with type 2 diabetes (stratified by age, sex, BMI and duration of diabetes) were following a weight-managemnent, a high-carbohydrate/fiber, or a modified-lipid diet.

Blinding used (if applicable)


Intervention (if applicable)

Detailed dietary advice was given at the time of randomization and was reinforced at regular intervals throughout the study.  Food displays, exchange lists, and recipes were provided, and participants' favorite recipes were adapted.  Several evening meals were organized in a social context to aid compliance.

Planned diet treatments are shown below.  All groups were asked to achieve and/or maintain BMI </equal to 25 kg/m2.  The weight management group was asked to restrict extrinsic simple sugars and energy-dense foods, but no advice on the specific distribution of nutrients.

Variables Modified lipid diet High-carbohydrate/fiber diet
Protein (% of energy) 19 15
Fat (% of energy) 36 30
Carbohydrate (% of energy) 45 55
Fiber (g/d) -- >30
SFA (% of energy) -- <10

Statistical Analysis

  • Analysis of variance ANOVA with Bonferroni's adjustment to maintain significance at 95% differences in clinical and lab measurements between the 3 diet groups
  • ANOVA as described by Zerbe (for changes over time by randomization.
  • Repeated measures ANOVA (testing significant changes)
Data Collection Summary:

Timing of Measurements

Recruitment (baseline); randomization (time 0, ~3 mo after recruitment); 1 and 3 mo after randomization, and then every 3 months for 18 months.  Nine months after completion of the study an attempt was made to reassess all participants.

Dependent Variables

  • HbA1 (column separation using an ion-exchange resin
  • plasma total cholesterol (enzymatic kits (Boehringer Mannheim)
  • plasma triglycerides ((enzymatic kits (Boehringer Mannheim)
  • HDL cholesterol (manganese-heparin precipitation
  • LDL cholesterol (calculated using the Friedewald equation

Independent Variables

  • Calories, macronutrients, fiber (24-hr recalls, analyzed using New Zealand Food Composition Tables and Englyst for the soluble fiber content of foods)

Control Variables

  • weight
  • diabetes medications
Description of Actual Data Sample:

Initial N: 70

Attrition (final N): 64 (35 women, 29 men).  2 participants moved from the region, 2 started insulin treatment, 1 diagnosed with cancer, 1 died.

Age: mean of 58-60 years

Ethnicity: not provided

Other relevant demographics:

  • Duration of diabetes - mean of 3.7-5.6 years
  • Other medications taken were for asthma, insomnia, and migraine

Anthropometrics: BMI: 29-30

Location: Department of Human Nutrition, University of Otago, Dunedin, New Zealand


Summary of Results:



Weight management (control) group average from month 9 to 18,  n=64


Modified-lipid group average from month 9 to 18, n=64


High-carbohydrate/fiber group average from month 9 to 18, n=64


Statistical Significance of Group Difference

Weight (kg)

79.8±2.7 82.1±3.2 80.7±3.0


GHb (%)





Total cholesterol (mM)





LDL-cholesterol (mM) 4.2±0.14 3.6±0.15 4.0±0.19 NS
HDL-cholesterol (mM) 1.18±0.05 1.22±0.06 1.19±0.06 NS
Triglycerides (mM) 1.6±0.15* 2.0±0.19 2.4±0.21 Significantly lower than the high-carbohydrate/fiber diet at the 95% level
Carbohydrate (% of energy) 47.6±1.6 46.4±1.6 46.6±1.6 NS
Fiber (g/d)  17.3±1.3  21.4±2.3  21.1±1.7 NS
Soluble fiber (g/d) 5.0±0.4* 6.2±0.6 6.8±0.6 *Significantly lower than the high-carb/fiber diet at the 95% level
Sucrose (g/d) 20.1±2.5 27.6±5.9 15.4±1.9* *significantly lower than the modified lipid diet group at the 95% level
Fat (% of energy) 33.6±1.4 33.9±1.3 32.4±1.5 NS
SFA (% of energy) 13.1±0.8 13.6±0.5 12.4±0.9 NS

  Other Findings

  • No overall significant changes were observed in weight during the study, and changes in weight were not correlated with changes in any other measured variable
  • When all groups were combined, glycemic control, total cholesterol and HDL-cholesterol all fell significantly between recruitment and randomization.
  • No differences were observed in lipid levels between those on medications known to influence lipid metabolism and those not taking these preparations.
Author Conclusion:
In the long term there were few differences in the outcome of the three dietary prescriptions.  Our findings suggest that focusing on increasing carbohydrate and fiber intake in the diet or replacing saturated fatty acids with unsaturated fats both result in metabolic improvement.  However, because participants found it difficult to meet either of these recommendations in full, advice to achieve moderate changes in both carbohydrate and fat intake may be more acceptable, more realistic, and therefore a more effective long-term dietary treatment for diabetes.
Funding Source:
Government: health research council of new zealand
Reviewer Comments:

This study is one of only a few to provide dietary interventions and then follow free-living adults for over a year.

In all diet groups, HbA1 fell significantly during the recruitment phase, perhaps due to increased attention.

The careful analysis (stratification for age, sex, BMI and duration for diabetes before randomization, and the ANOVA and repeated measures ANOVA statistical analyses) provide the reader a level of confidence in the results of the study.

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? ???
  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? 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? ???
  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? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  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? 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