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DF: Diabetes (2008)

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

To determine whether diet supplementation with arabinoxylan-rich (AX) fiber from wheat improves glycemic control in Type II diabetes.

Inclusion Criteria:

Type II diabetes.

Exclusion Criteria:

None specified.

Description of Study Protocol:

Recruitment

Participants were recruited from a Brunswick Community Health Center, Melbourne, Australia.

Design

  • Subjects followed habitual diet and replaced starchy food with control or AX-enriched bread for five weeks
  • Seven subjects started the AX diet first, while eight subjects started the control diet first
  • Without washout, patients were crossed-over to the alternate arm at the end of five weeks.
  • Subjects were assessed for the following at the beginning and the end of each dietary period (baseline, Week Five, Week 10):
    • Oral glucose tolerance test (OGTT) (75g)
    • Laboratories: Venous blood samples were collected during the fasting state
      • Glucose, insulin, fructosamine, total cholesterol, HDL, triglycerides.
    • Blood pressure, total body weight and body fat mass (whole body densitometry scan).
  • Dietary compliance
    • Self-report (questionnaire): Subjects were asked to indicate how often they had consumed the bread and muffins supplied to them. Five phrases (bread and muffins eaten 0%, 25%, 50%, 75% and 100% of the time) were used and responses were rated on a score from one (0% of the time) to five (100% of the time)  
    • Fecal analysis (weight and polysaccharide secretion): A 24-hour fecal sample was collected during the last three days of each diet from 12 of 15 subjects
    • Seven-day food diary (last week of each dietary period): Each subject received a set of standard measuring cups and spoons and detailed instructions for recording food intakes.
  • Palatability: At the end of each diet, subjects were asked to rate their response to the bread or muffins on a structured scale with nine categories: 'Like extremely' (score=1) to 'dislike extremely' (score=9)
  • GI tolerance: At the end of each diet, subjects were asked to score the daily frequency of their bowel movements on a scale in nine categories ranging from one ('much less than usual') through five ('usual') to nine ('much greater than usual').  Also, there was a side-effects questionnaire relating to high fiber intake.

Blinding

Single: Participants (but not investigators) were masked.

Intervention

Participants followed their habitual diet, but replaced the majority of their starchy foods with specified quantities of control or AX-fiber-enriched bread and muffins. Subjects were required to eat four or five slices of bread and one or two muffins per day, depending on energy requirements. The AX diet provided 14g to 17g of fiber per day from nonstarch polysaccharides (NSP).

All bread and muffins were prepared to standard recipes by a professional baker who ensured that control and test breads presented with similar flavor, color and texture. Control bread and muffins were made with 50% whole wheat and 50% white flour. AX bread and muffins were made with 50% whole wheat, 36% white flour and 14% AX-rich fiber. The AX-rich fiber contained no fat and little protein (10% weight) or starch (15%). It comprised mainly NSP (70%), particularly soluble NSP (ratio of soluble to total NSP, 0.62).

Statistical Analysis

  • Two-tailed paired Student's T-tests: Comparison of nutrient intakes and fecal parameters
  • General linear model (GLM) for crossover design (differences between arms)
  • Differences between the two arms of the crossover study were evaluated
  • Wilcoxon's signed ranks: Differences in questionnaire responses.
Data Collection Summary:

Timing of Measurements

 At the beginning and end of each diet period (baseline, Week Five, Week 10)

  • Oral glucose tolerance test (OGTT): 75g
  • Laboratories: Venous blood samples were collected during the fasting state
    • Glucose
    • Insulin
    • Fructosamine
    • Total cholesterol
    • HDL
    • Triglycerides.
  • Blood pressure, total body weight and body fat mass (whole-body densitometry scan).

Dietary compliance was assessed by:

  • Self-report: Questionnaire
  • Fecal analysis (weight and polysaccharide secretion): A 24-hour fecal sample was collected during the last three days of each diet from 12 of 15 subjects
  • Seven-day food diary (last week of each dietary period): Each subject received a set of standard measuring cups and spoons and detailed instructions for recording food intakes.

Dependent Variables

  • Glucose
  • Insulin
  • Fructosamine
  • Total cholesterol
  • HDL
  • Triglycerides.

Independent Variables

 Quantity of AX-fiber consumed.

Covariates

N/A.

Description of Actual Data Sample:
  • Initial N: 15 (nine female, six male)
  • Attrition (final N): Three incomplete fecal samples (15 for blood sample outcomes)
  • Age: 60±2 years
  • Ethnicity: Not reported.

Other Relevant Demographics

  • Mean duration DM: 2.3±0.6 years
  • HgbA1c: 6.3±0.2%
  • Fasting glucose: 7.5±0.3mmol per L
  • Two-hour post-prandial glucose: 15.1±0.9mmol per L
  • Normolipemic
  • Normotensive.

Medication Use

  • 10 subjects depended on diet therapy alone 
  • Five subjects taking low-dose oral hypoglycaemic agents
  • None required insulin
  • Two subjects took lipid-lowering medications
  • Nine took antihypertensive agents.

Anthropometrics

Body mass index of 28.1±0.9kg per m2.

Location

Brunswick Community Health Centre, Melbourne, Australia.

Summary of Results:

Dietary Intake

  Control Fiber
Energy (kcal) 2,065±15kcal 2,072±15kcal
Carbohydrate (% Kcal) 55±1% 55±2%
Fiber (g1000 Kcal) 16±1g per 1,000kcal 24±1g per 1,000kcal

Glucose, Insulin, and Lipid Levels

Parameter (N=15)
Control Diet
AX Diet
Week Zero
Week Five
P-Value
Week Zero
Week Five
P-Value
Plasma glucose (mmol/l)  Fasting 7.3±0.3 7.6±0.3 NS 7.6±0.3 7.0±0.3 P<0.002
Two h post-OGTT 14.5±0.9 15.0±0.8 P=0.3 15.2±0.9 13.4±0.9 P<0.001
Serum insulin (pmol/l)
Fasting 90±10 85±10 NS 98±10 77±6 P<0.05
Two h post-OGTT 587±173 638±170 P=0.3 656±174 493±121 P<0.02
Serum fructosamine (mmol/l) 267±9 272±10 P=0.07 271±9 266±9 P=0.07
Body weight (kg)  Total 77.5±3.3 78.2±3.3 NS 77.8±3.3 78.1 3.3 NS
Fat mass 28.7±2.2 29.1±2.1 NS 28.7±2.2 28.7±2.2 NS
Blood pressure (mmHg)  Systolic 140±5 139±5 NS 139±4 136±4 NS
Diastolic 75±2 77±2 NS 77±2 75±2 NS
Serum lipids (mmol/l)  Total cholesterol 5.43±0.23 5.33±0.24 NS 5.31±0.25 5.31±0.23 NS
HDL 1.06±0.04 1.04±0.05 NS 1.04±0.05 1.04±0.04 NS
LDL 3.53±0.22 3.35±0.26 NS 3.36±0.26 3.32±0.21 NS
Triacylglycerol 1.86±0.27 2.06±0.39 NS 2.01±0.35 1.86±0.29 NS
  • Between-diet difference in glucose, two-hour post-OGTT significantly lower in the AX diet (P<0.001)
  • Between-diet difference in insulin, two-hour post-OGTT significantly lower in the AX diet (P<0.015)
  • Significant between-diet difference in fructosamine (P<0.001)
  • No difference in weight, fat mass, cholesterol DL, LDL or triglycerides.

Other Findings

  • Acceptance
    • Acceptance similar for bread [five (four to six) and five (three to seven), control and AX, respectively: P=0.63] and for muffins [five (three to six) and four (three to six), control and AX, respectively; P=0.89]
  • Compliance
    • Compliance similar between control and AX-rich foods: Median score, five (four to five) in each case.
  • Elimination
    • More bowel movements per day on the AX diet than on the control diet: Score, seven (five to eight) vs. five (five to seven); median, 25th to 75th percentile, AX diet and control diet, respectively; P<0.05
    • Mean fecal output was significantly higher on the AX diet than after the control diet (284±36g and 223±30g per day, respectively; P=0.05)
    • Fecal output tended to have higher dry weight (63±7g and 53±7g per day, respectively; P=0.06)
    • Polysaccharide (i.e., NSP+RS) content of the feces was significantly higher after the AX diet (15.1±2.9g and 17.3±2.8g per day, control and AX diet, respectively; P=0.02).
Author Conclusion:

Supplementation with 15g non-starch polysaccharide in the form of AX-rich fiber extracted from the byproduct of wheat flour processing has beneficial effects on insulin and glucose control in people with type II diabetes.

Funding Source:
Government: Office of Science and Technology of Jiangsu Province, Bureau of Science & Technology of Nantong City
Reviewer Comments:
  • No description of inclusion or exclusion criteria 
  • No description of randomization of order of treatment assignments, "but not found to affect any measured variables"
  • No exploration of potential confounding variables.
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? N/A
  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? N/A
  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? 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? Yes
  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? 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? 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)? Yes
  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? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? No
  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