DF: Cardiovascular Disease (2008)

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

To investigate whether a dietary fiber supplement given as fiber tablets could influence weight, serum lipids and blood pressure.

Inclusion Criteria:
  • Age 30 to 60 years
  • Body weight greater than 115% of ideal body weight.
Exclusion Criteria:
  • History of gastrointestinal diseases
  • Use of bulk laxatives, H2-blockers or diuretics.
Description of Study Protocol:
  • Recruitment: Subjects recruited from four centers of a weight reduction club
  • Design: 1,200-calorie diet with a fiber content of 25 grams, in combination with either a dietary fiber preparation or a placebo
  • Blinding used: The placebo and fiber supplements were identical in appearance.

Intervention

  • Fiber or placebo tablets were distributed on a random basis
  • Dosage was five tablets taken together with 300ml of water four times a day, 30 minutes before each of the four main meals
  • The fiber tablets contained 24kcal and six grams of fiber from cereals and citrus fruits
  • The placebo tablets contained 84kcal and one gram of fiber.

Statistical Analysis

  • 95% confidence intervals estimated using the Student and Bernoulli-Wilcoxon procedures. All tests were one-tailed.
  • Comparisons between the groups were carried out according to the Wilcoxon two-tailed test
  • The Wilcoxon one-tailed test was used for changes within groups.
Data Collection Summary:

Timing of Measurements

  • Measurements taken at baseline and after 12 weeks of treatment
    • Weight
    • Serum lipids
    • Blood pressure.
  • Compliance with supplement routine: Participants were asked to bring all remaining supplements to each visit for counting.

 Dependent Variables

  • Weight
  • Serum lipids
  • Blood pressure.

Independent Variables

Fiber supplement intake.

Control Variables

None.

 

Description of Actual Data Sample:
  • Initial N: 70 women
  • Attrition (final N): 60 (29 fiber; 31 placebo); 10 withdrawals not related to the treatment
  • Age: Median age, 35 for both groups
  • Ethnicity: Not specified
  • Other relevant demographics: None described
  • Anthropometrics: Both groups comparable regarding height 
  • Location: Denmark.
Summary of Results:

Variables

Fiber Group, Pre-Treatment

Control Group, Pre-Treatment

P-Value (Between Groups)

Fiber Group, Post-Treatment

Control Group, Post-Treatment

P-Value (Between Groups)

Systolic Blood Pressure, mm/Hg

123
(115-131)

142
(130-154)

<0.01

114
(110-119)

142
(132-153)

<0.01

Diastolic Blood Pressure, mm/Hg

84
(77-91)

95
(87-103)

<0.02

75
(70-81)

91
(85-98)

<0.01
Serum Cholesterol, mmol/l

6.1
(5.2-7.1)

6.3
(5.6-7.1)

NS

5.6
(4.7-6.4)

5.7
(4.1-6.5)

NS
Serum Triglycerides, mmol/l

1.52
(1.16-1.58)

1.56
(1.20-1.90)

NS

1.15
(0.90-1.40)

1.18
(0.93-1.41)

NS
 

Other Findings

  • Weight loss: During treatment, both groups lost weight significantly (P<0.01). The mean weight loss in the fiber groups (8.5kg)was significantly greater compared to the placebo group (6.4kg, P<0.01).
  • Blood pressure: At baseline, the fiber group had significantly lower systolic blood pressure than the placebo group (P<0.05). During treatment, blood pressure dropped significantly (P<0.05) only in the fiber group, remaining constant in the placebo group.
  • Serum lipids: Both serum triglycerides and serum cholesterol were reduced after treatment in both groups (P<0.02), but there was no signifcant difference between groups.
Author Conclusion:
  • Adding a dietary fiber supplement of six grams per day to a hypocaloric diet leads to a significantly lower body weight 
  • Loss of body weight in itself may lead to a reduction in blood pressure. Adding a fiber supplement to the diet regimen may cause a reduction in blood pressure.
  • The authors were not able to confirm that fiber may have a reducing effect on triglyceride and cholesterol concentrations.
Funding Source:
Reviewer Comments:
  • There was very little description given about the methods used for assessing blood pressure or serum lipids, so the results might not compare with other studies
  • One author appears to be associated with a company called "Farma Food," which could possibly be the manufacturer of the fiber tablet used. The funding source for this study was not indicated and I am not familiar with Danish supplement companies. As such, it is unclear whether there is a potential for conflict of interest in this study.
  • The fiber content of the subjects' diets was not measured, so we don't know what the overall fiber intake was for the two groups. The study would be stronger if it was shown that both groups had comparable fiber intakes, independent of the fiber supplement.
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? No
  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? No
  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? 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? No
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? No
  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? 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? No
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? No
  10.2. Was the study free from apparent conflict of interest? Yes