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DF: Cardiovascular Disease (2008)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To assess the efficacy of 7.95g fiber as psyllium and beta-glucan per day consumed in four servings to lower serum lipid risk factors for cardiovascular disease.
Inclusion Criteria:
  • Elevated LDL-C (over 4.1mmol per L)
  • Men or post-menopausal women.
Exclusion Criteria:
  • Clinical or biochemical evidence of diabetes, liver disease or renal disease
  • Use of hyperlipidemic agents
  • Smoking.
Description of Study Protocol:

Recruitment

No information provided. 

Design

  • Randomized crossover trial
  • Subjects randomized to one of two treatment groups in a crossover design
  • The month-long treatment phases were separated by a two-week washout period. 

Blinding

Not mentioned.

Intervention

  • Each subject completed two diet phases in random order with instructions to follow the National Cholesterol Education Program (NCEP) Step II diet throughout the study
  • Test and control study foods were substituted for some foods normally consumed so body weight would be maintained.
  • High-Fiber Diet Phase: Included 36.2% of kcalories from a selection of high-fiber foods providing 1.8g to 2.5g psyllium or 0.75g beta-glucan per serving. Four servings, including one breakfast cereal and one frozen dinner per day were consumed. High-fiber food selections included breakfast cereals, breads, pasta-based frozen dinners, tea cakes, cookies, potato chips and smoothie beverages.
  • Control Diet Phase: Provided similar commercial foods as those listed above for the High-Fiber Diet, without the added fiber.

Statistical Analysis

  • Means of Weeks Two and Four for each diet phase were used for analysis of treatment differences
  • The percentage difference between treatments was determined by two-tailed Student's T-test for paired data
  • The absolute difference between treatments was analyzed by ANCOVA with the general linear model procedure used
  • Covariates were diet, sex x sequence interaction and a random term representing the subject nested within the sex x sequence interaction and the baseline value.
Data Collection Summary:

Timing of Measurements

  • BP was measured at the start and end of Weeks Two and Four of each phase
  • Body weight was measured at the start and bi-weekly during both diet phases. 

Dependent Variables

  • SBP measured with subjects seated and fasted for 12 to 14 hours overnight
  • DBP measured with subjects seated and fasted for 12 to 14 hours overnight
  • Serum lipids
  • GI symptoms obtained by subject report.

Independent Variables

  • High-Fiber Diet Phase of an average of and additional 7.2g psyllium and 0.75g beta-glucan, consumed daily to a NCEP step II diet
  • Control Diet Phase of no additional fiber and consumption of the NCEP step II diet.
Description of Actual Data Sample:
  • Initial N: 92 subjects were recruited; 82 were available for randomization
  • Attrition (final N): 68 (37 men, 31 post-menopausal women). 17% dropout rate.
  • Age: 60±1 years (mean±SE) with a range of 33 to 82 years of age
  • Ethnicity: Not mentioned
  • Other relevant demographics: None mentioned.

Anthropometrics

  • BMI: 25.6±0.3 (range, 20.0-33.8)
  • Body weight (kg) at baseline and the mean of weight at Weeks Two and Four of the control diet was 71.7±1.5 and 71.6±1.4, respectively
  • Body weight at baseline and the mean of weight at Weeks two and Four of the high-fiber diet was 71.7±7 and 71.6±1.4
  • There was no difference in weight between the diet phases.

Location

Toronto, Canada.

Summary of Results:

SBP and DBP tended to be reduced after both dietary phases, but were not different between treatments (data presented below).

 
Control Baseline
Control
Mean Treatment
High Fiber Baseline
High Fiber Mean Treatment
Mean Treatment Difference, %
P-Value
SBP, mmHg
124±2
122±1
124±2
121±1
-0.7±0.4
0.061
DBP, mmHg
80±2
76±1
79±2
77±2
-0.3±0.6
0.406

Other Findings

  • The percentage mean treatment difference in body weight was 0.1±0.1, P=0.494 and weights were not different between the two dietary phases
  • Reductions in blood lipids were seen post-treatment for both diets
  • Total cholesterol, triglycerides, apolipoprotein B, total:HDL-C and LDL-C:HDL-C were lower post-treatment, following the high-fiber diet than for the control diet, P<0.04.
Author Conclusion:
The reduction in serum lipid risk factors for cardiovascular disease support the FDA's approval of a health claim for a dietery fiber intake of four servings per day.
Funding Source:
Government: natural sciences engineering research council of Canada
Industry:
Kellogg Company
Food Company:
Reviewer Comments:
  • The author's conclusion is focused on changes in serum lipids and emphasizes use of fiber spread out through the day and potential benefit on a population basis
  • Compliance was measured by weighing food items and diet records; compliance was considered to be good
  • The potential confounder of race was not discussed, however alcohol intake, activity, smoking, diet and stable weight were considered.
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? ???
  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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
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.) 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? ???
  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%.) ???
  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? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? ???
  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.) ???
  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? ???
  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? ???
  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? ???
  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? 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