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HTN: Fiber (2007)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To determine the impact of dietary patterns on the control of hypertension.
Inclusion Criteria:
  • 29% of original DASH participants had Stage I hypertension (133 subjects)
  • SBP of 140 - 159 mmHg
  • DBP of 90 - 95 mmHg
  • Adults age 22 or older 
  • Persons previously using antihypertensive medication were eligible for entry only after a period of supervised medication withdrawal that preceded the screening process by at least 2 weeks.
Exclusion Criteria:
  • Poorly controlled diabetes mellitus or hyperlipidemia
  • Cardiovascular event within the prior 6 months
  • Chronic diseases that may interfere with participation
  • Pregnancy or lactation
  • BMI > 35
  • Concurrent use of medications affecting blood pressure
  • Unwillingness to discontinue vitamin and mineral supplements or antacids containing magnesium or calcium
  • Renal insufficiency
  • Alcohol intake of more than 14 drinks per week
Description of Study Protocol:


Subjects were a subgroup of the DASH study.


Randomized Controlled Trial.

Blinding used (if applicable)

Not possible - lab tests.

Intervention (if applicable)

Participants fed a control diet for 3 weeks and then were randomized to receive either 8 weeks of either:

  • control diet
  • a diet rich in fruits in vegetables but otherwise similar to control
  • a combination diet rich in fruits, vegetables, low-fat dairy products, including whole grains, fish, poultry, and nuts, and reduced in fats, red meats, sweets, and sugar-containing beverages

Statistical Analysis

Analyses performed on intent-to-treat basis.  Pairwise comparisons of changes in blood pressure between diets from baseline to end of intervention were analyzed by Student's t test in unadjusted analyses and by ANOVA in adjusted analyses.  Relative risks of HTN at the end of the intervention period were computed with 95% confidence intervals.

Data Collection Summary:

Timing of Measurements

Study was conducted in 3 phases:  screening for eligibility, 3 week run-in feeding period, and 8-week intervention feeding period. Weight measured each weekday, and blood pressure measured once weekly.  Urine samples collected at the end of run-in and intervention periods.

Dependent Variables

  • Blood pressure measured by trained and certified staff members using random-zero sphygmomanometer
  • Urinary excretions of sodium, potassium, calcium and magnesium determined from 24-hour urine samples 

Independent Variables

  • Control diet, fruits and vegetables diet or DASH diet
  • Meals prepared in metabolic kitchens

Control Variables

  • Clinical center
  • Gender
  • Race
  • Age
  • Alcohol intake
  • Baseline BP
Description of Actual Data Sample:

Initial N: 133 participants, 60% women.

Attrition (final N):  47 received control diet (94% completed), 49 received fruits and vegetables diet (96% completed), and 37 received DASH diet (100% completed).

Age:  mean age 49.2 +/- 10.3 years

Ethnicity:  65% black 

Other relevant demographics:

Anthropometrics:  No significant differences between groups.

Location: United States


Summary of Results:


  HTN at End of Intervention (%) Relative Risk (95% CI)

P value

Control Diet 36/47 (77%) 1.00  

Fruits & Vegetables

27/49 (55%

0.72 (0.52, 0.97)



11/37 (30%)

0.39 (0.23, 0.65)


Other Findings

Sodium intake and body weight were held constant throughout the study.

The combination diet significantly reduced SBP (-11.4 mmHg, P < 0.001) and DBP (-5.5 mmHg, P < 0.001).

The fruits and vegetables diet also significantly reduced SBP (-7.2 mm Hg, P < 0.001) and DBP (-2.8 mm Hg, P = 0.013).

The combination diet produced significantly greater BP effects (P < 0.05) than the fruits and vegetables diet.

Blood pressure changes were evident within 2 weeks of starting the intervention feeding.

After the 8-week intervention period, 70% of participants eating the combination diet had a normal BP (SBP < 140 and DBP < 90 mm Hg) compared with 45% on the fruits and vegetables diet and 23% on the control diet. 

Author Conclusion:
In conclusion, a diet that emphasizes fruits, vegetables, and low-fat dairy products, includes whole grains, poultry, fish and nuts and is reduced in fat, red meats, sweets, and sugar-containing beverages led to significant hypertension control in persons with Stage I hypertension.
Funding Source:
Government: NHLBI
Reviewer Comments:
Foods provided to participants.
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? ???
  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? 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.) 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)? Yes
  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