Fiber

DF: Cardiovascular Disease (2008)

Citation:

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

Study Design:

Randomized Crossover Trial

Class:

A - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To determine the effect of high fiber rye bread on glucose and insulin metabolism in healthy post-menopausal women.

Inclusion Criteria:

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.

Exclusion Criteria:

Lipid-lowering drug use
Laxative drug use
Corticosteroid medications
Diagnosed or undiagnosed diabetes mellitus, by screening using glucose tolerance tests
Pre-menopausal.

Description of Study Protocol:

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.
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.

Data Collection Summary:

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.

Description of Actual Data Sample:

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.

Summary of Results:

		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.

Author Conclusion:

There was no effect of dietary carbohydrate or fiber modification on fasting glucose and insulin concentrations.

Funding Source:

Industry:

Fazer-Bakeries Ltd, Vaasan & Vaasan Oy (both Finland)

Food Company:

Not-for-profit

Foundation associated with industry:

Reviewer Comments:

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
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