DF: Cardiovascular Disease (2008)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine the effects of two whole grain oat-based cereals, rich in soluble fiber added to the diet, compared with two wheat-based cereals on the need for antihypertensive medications in people with hypertension and hyperinsulinemia.
Inclusion Criteria:
Men and women being treated for hypertension with a mean baseline BP under 160/100.
Exclusion Criteria:
  • History of SBP over 180mm Hg or DBP over 115mm Hg
  • History of existing complications of hypertension, especially MI, angina pectoris, stroke or impaired renal function
  • History of major intestinal surgeries, malabsorption, sentosis of the GI tract or biliary disease
  • Use of beta-adrenergic receptor blocking agents
  • Diabetes mellitus
  • BMI over 35
  • History or signs of excessive use of alcohol (more than two drinks per day)
  • Current smoking
  • High soluble fiber intake (six grams per day)
  • Chronic use of antacids, bulk laxatives or other medications affecting the GI tract
  • Continuous treatment with estrogen replacements at dosage above two mg or unstable dosage
  • Participation in another intervention study three months before randomization.
Description of Study Protocol:
  • Recruitment: Letters were sent to 8,000 potential participants identified from a database of treated hypertensive patients obtained from a local HMO
  • Design: Randomized controlled parallel-group trial of three four-week phases, including baseline feeding phase, medication reduction phase and a maintenance phase
  • Blinding used: Data collectors were also blinded to group randomization.


Two types of intervention occurred: Cereal was added to the diet and medication was reduced during the second phase of the study. Cereal treatments were isocaloric and administered during all three study phases. 

  • Oats Group: 60g (approximately 3/4 cup) of Quaker Oatmeal and 77g (approximately 1-1/3 cups) of Quaker Oat Squares were added to the diet daily. The cereals provided 11.69g of total fiber, 6.23g of soluble fiber and 5.42g of beta-glucans
  • Control Group: 65 grams (1.2 cup) Malt-O-Meal Hot Wheat Cereal and 81 grams (two cups) of Kellogg's Crispix were added to the diet daily. These cereals provided 3.52g total fiber and less than 1.1g soluble fiber.

Medication reduction: At Week Four, medication dose was reduced to half if:

  • BP was below 10mm Hg above the baesline measurement and
  • BP was below 140/90mm Hg if baseline measures were below 140/90 or
  • BP was below 160/100 if baseline measures were between 140/90 and 160/100.

At Week Six, medication was altered as follows:

  • Medication was discontinued if the conditions listed above prevailed
  • Medication was resumed to full dose if:
    • BP had increased more than 10mm Hg since baseline and
    • BP exceeded 140/90mm Hg for those with baseline values under 140/90mm Hg or
    • BP exceeded 160/100mm Hg if baseline values were between 140/90mm Hg and 160/100mm Hg.

During seven to 12 weeks, medication was resumed in half dose increments if:

  • BP of those on no dose increased by 10mm Hg or
  • BP was over 140/90mm Hg if baseline was under 140/90mm Hg
  • BP was over 160/100mm Hg if baseline was between 140/90 and 160/100mm Hg.
Statistical Analysis
  • A power test was completed set at a 0.5 significance level and 80% to detect a 15% difference in medication reduction
  • Differences in mediation reduction were determined by chi-square test of proportions
  • Student's paired and unpaied T-tests were used to determine differences within and between groups
  • Multiple regression adjusted for blood lipis and glucose levels and BP findings for confounding
  • The population was considered as an intent-to-treat sample and all patients were included in the analyses.
Data Collection Summary:

Timing of Measurements

BP was measured twice each week during the baseline phase (Weeks One through Four), weekly during the medication reduction phase (weeks Four through 12) and twice each week during the maintenance phase (weeks 13 through 18). 

Dependent Variables

  • Medication reduction from baseline dose
  • Change in SBP and DBP from baseline in those without medication reduction measured after resting while seated for over five minutes with a column sphygmomanometer. The mean of three readings was used.
  • Medication resumption during the six-week follow-up phase.

Independent Variables

  • Fiber from oats products added to the diet providing 11.69g of total fiber, 6.23g of soluble fiber, 5.42g of beta-glucans
  • Fiber from wheat products added to the diet providing 3.52g total fiber and less than 1.1g soluble fiber.
Description of Actual Data Sample:
  • Initial N: 524 respondents to initial mailing were screened via phone; of these, 212 passed the initial phone screen; of these, 88 met BP criteria and were enrolled.
  • Attrition (final N): 88 (45 men). There was no attrition.


  • Oats group: 48.7±16.9 (mean±SD) years
  • Control (wheat) group: 46.4±15.3 years
  • Total age span: 33-67 years.


96% of oats group and 98% of control group were Caucasian.


  • Oats group BMI: 31.2±5.1
  • Control group BMI: 30.6±4.7
  • The BMI means were not different between groups. 


Minneapolis, MN.

Summary of Results:

Antihypertensive medication, BP, Lipid, and Weight changes by group

Oats Group
Control Group
BP medication reduction, N (%)
33 (73%)
18 (42%)
SBP change for those without medication reduction, mm Hg
DBP change for those without medication reduction, mm Hg
BP medication resumption, N (%)
23/33 (67%)
6/18 (33%)
Total Cholesterol -31.7mg/dl (15%) -7.5mg/dl p<0.05
LDL-C -22.3mg/dl (16%) -6.1mg/dl p<0.05
HDL-C +1.5 mg/dl -1.0mg/dl NS
Triglycerides -12.8mg/dl -7.4mg/dl NS
Weight +0.5kg -0.3kg NS
Glucose -12.3mg/dl +2.7mg/dl p<0.05

Other Findings 

  • No weight changes occurred in either group during the study
  • Total fiber increased more in the treatment than the control group
  • 75% of the oats group participants reduced their BP medication, while only 42% of the control group were able to reduce their medication. Those who did not reduce their medication had a seven-mm Hg reduction in SBP and four-mm Hg reduction in DBP (P-value not given), while the smaller changes in the control group were not significant. 
  • During the follow-up phase, 33% of the control group and 67% of the treatment group resumed taking medication (P not given)
  • Mean BP in the treatment group was lowered from 140/88mm Hg at baseline to 134/85mm Hg at four weeks with SBP, P<0.05 
  • Total cholesterol and LDL-C in the treatment group decreased by 31.7mg per dL (15%) and 22.3mg per dL (16%), respectively. Glucose levels in the treatment group decreased by 12mg per dL. These changes were different from the control group, P<0.05.
  • Significant decrease in glucose from baseline in oat group (p<0.05)
  • The frequency of side effects decreased by 22% in the treatment group, whereas no change in side effects was observed in the control group.
Author Conclusion:
A diet containing soluble fiber-rich whole oats can significantly reduce the need for antihypertensive medication and improve BP control among treated hypertensives.
Funding Source:
Reviewer Comments:
  • Compliance was determined by measuring returned cereal and subject records and was high, based on these measures
  • Subjects were asked to maintain usual activity, diet and weight during the study
  • Effects of whole food intervention were studied rather than supplementation
  • Weight change, sodium and alcohol intake were controlled for. 
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) 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? 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)? 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? N/A
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