DF: Cardiovascular Disease (2008)
Juntunen, KS, Laaksonen DE, Poutanen KS, Niskanen LK, Mykkanen HM. High-fiber rye bread and insulin secretion and sensitivity in healthy postmenopausal women. Am J Clin Nutr. 2003; 77: 385-391.
PubMed ID: 12540398
To determine the effect of high fiber rye bread on glucose and insulin metabolism in healthy post-menopausal women.
- Post-menopausal: As determined by measured serum follicle-stimulating hormone concentrations
- Serum total cholesterol: 5.0 to 8.5mmol per L
- Non-HDL-cholesterol: 3.5 to 6.5 mmol per L
- Serum total triacylglycerol: Under 2.5mmol per L
- BMI: 20 to 33.
- Lipid-lowering drug use
- Laxative drug use
- Corticosteroid medications
- Diagnosed or undiagnosed diabetes mellitus, by screening using glucose tolerance tests
- Pre-menopausal.
Recruitment
Not described.
Design
- 20 post-menopausal women were randomly assigned to an eight-week test diet, which included two different fiber-containing breads: High-fiber rye vs. white wheat bread
- There was an eight-week washout period between treaments
- There was a two- to three-week run-in period, during which the women were advised to maintain diet and exercise habits
- During the study periods, subjects were advised to eat the test bread in quantities corresponding to their habitual cereal consumption; no maximum amount was suggested
- Compliance was measured by daily bread use records and four-day food records
- Data was collected according to the following schedule:
- Four-day food diary: Run-in period, weeks four to six of bread periods
- Frequently sampled intravenous glucose tolerance test (FSIGTT): End of run-in period, end of bread periods
- Fasting plasma glucose: Beginning of bread periods
- Fasting serum insulin: Beginning of bread periods
- Weight: Every two weeks.
Blinding Used
Not described.
Intervention
- Women were randomly assigned to an eight-week test diet, which included two different fiber-containing breads: High-fiber rye vs. white wheat bread
- Following an eight-week washout period, the subjects crossed-over to the other diet
- There was a two- to three-week run-in period, during which the women were advised to maintain diet and exercise habits
- During the study periods, subjects were advised to eat the test bread in quantities corresponding to their habitual cereal consumption; no maximum amount was suggested
- Compliance was measured by daily bread use records and four-day food records
Bread |
Energy |
Fiber per Slice |
Slices per Day |
High Fiber Rye |
206kJ |
4.4g |
4-5 |
White Wheat |
241kJ |
0.6g |
4-5 |
Intakes were monitored for bread consumption to be 20% of daily energy intake or four to five portions per day
- High-fiber rye bread: About 17% dietary fiber; minimum consumed, about 7.5±1.4 portions per day; consumption, 8.1±1.6 portions per day
- White-wheat bread: About 2.8% dietary fiber; minimum consumed, about 6.2±1.2 portions per day; consumption, 7.7±1.6 portions per day.
Statistical Analysis
P<0.05, standard for statistically significant
- Diet analysis
- Percentage change in nutrient intakes from the run-in period to each treatment period
- Log transforamtion for comparison with Wilcoxon's rank-sum test for dependent data
- Energy intakes varied by treatment, thus protein and total fat intakes were treated as
covariates.
- Percentage change in nutrient intakes from the run-in period to each treatment period
- Blood values
- Intravenous glucose tolerance tests: Glucose effectiveness (Sg), insulin sensitivity (S1), acute insulin response (AIR)
- AIR transformed logarithmically and the all values proportionally change from run-in period for rye bread and wheat bread
- Analyzed by analysis of covariance with repeated measures
- Body weight did not change, so it was not used as covariate
- Non-parametric Freidmen's test
- Frequency of exercise in run-in, rye and wheat bread
- Non-parametric Mann-Whitney U test for independence
- Use of thyroid hormones, estrogen replacements therapy and body weight.
- Intravenous glucose tolerance tests: Glucose effectiveness (Sg), insulin sensitivity (S1), acute insulin response (AIR)
Timing of Measurements
Data was collected according to the following schedule:
- Four-day food diary: Run-in period, weeks four to six of bread periods
- Frequently-Sampled Intravenous Glucose Tolerance Test (FSIGTT): End of run-in period, end of bread periods
- Fasting plasma glucose: Beginning of bread periods
- Fasting serum insulin: Beginning of bread periods
- Weight: Every two weeks
- Daily exercise: Recorded for two-week baseline.
Dependent Variables
- Plasma glucose during intravenous glucose tolerance tests
- Plasma insulin during intravenous glucose tolerance tests
- Sg; glucose effectiveness
- S1; insulin sensitivity
- AIR; acute insulin response.
Independent Variables
- Carbohydrate intake
- Quantity of Fiber Intake.
Control Variables
Body weight.
- Initial N: 22 (no males, 22 females)
- Attrition (final N): 20 (no males, 20 females)
- Age: 59±6 years
- Ethnicity: Not described.
Other Relevant Demographics
- Serum total cholesterol: 6.5±0.8mmol per L
- Serum HDL cholesterol: 1.6±0.3mmol per L
- Serum triacylglycerol: 1.2±0.4mmol per L
- Plasm glucose: 5.4±0.4mmol per L
- Plasma insulin: 57.9±22.4pmol per L.
Anthropometrics
BMI: 27.5±2.9.
Location
Kuopio Unviersity Hospital; Kuopio, Finland.
Run-In |
Rye Bread |
White Bread |
Statistical Effects of Treatments |
||
Component
|
Protein |
17±3.2g |
19±2.8g |
17±1.9g |
Run-in period to rye bread > run-in period to white bread; P<0.05 |
Total fat |
31±6.1g |
27±4.7g |
30±5.5g |
Run-in period to rye bread < run-in period to white bread; P<0.05 |
|
Total fiber |
23.3±7.3g |
45.5±8.8g |
14.4±4.1g |
Run-in period to rye bread > run-in period to white bread; P<0.05 |
|
Soluble fiber |
5.6±1.7g |
9.0±1.8g |
4.7±1.6g |
Run-in period to rye bread > run-in period to white bread; P<0.05 |
|
Insoluble fiber |
10.5±3.5g |
32.6±6.2g |
5.8±1.3g |
Run-in period to rye bread > run-in period to white bread; P<0.05 |
|
Effect on Outcomes
|
SG, glucose effectiness |
0.025±0.004 |
|
0.023±0.006 |
NS |
SI, insulin sensitivity |
4.6±2.0 |
4.1±2.1 |
3.9±1.8 |
NS |
|
AIR, acute insulin response |
2,561±1,373 |
2,904±1,749 |
2,651±1,632 |
Run-in period to rye bread period > run-in period to the white bread period; P=0.047 |
Insulin
- No significant change in insulin concentration with either bread
- Bread type had an effect on insulin concentration (P=0.006).
Glucose
- No significant change in glucose concentration with either bread
- Dietary protein (P=0.028) and dietary fat (P=0.048) had an association with glucose concentration.
No Significant Effects
- Cholesterol
- Fasting glucose
- Fasting insulin levels
- AUC plasma glucose
- AUC plasma insulin.
Other Findings
- No difference in intake from run-in, except in
- Greater intake of protein (P=0.007)
- Lower intake of fat (P=0.033).
- No change in body weight over study period.
There was no effect of dietary carbohydrate or fiber modification on fasting glucose and insulin concentrations.
Industry: |
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Not-for-profit |
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- Small sample size
- Power calculations were not done
- Lack of much variance in the fiber soluble intake
- 20% carbohydrates provided as bread, however compliance appeared good.
In general, there was not a strong result to support increasing rye bread fiber intake as a method to control against development of type 2 diabetes in this group of women. Probably, the etiology is too complicated for one dietary treatment.
Quality Criteria Checklist: Primary Research
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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? | Yes | |
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? | 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? | Yes | |
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.) | No | |
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? | 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? | 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? | 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? | 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 | |