HTN: Fiber (2007)
- 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.
- 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
Recruitment
Subjects were a subgroup of the DASH study.
Design
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.
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
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
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) |
0.027 |
Combination |
11/37 (30%) |
0.39 (0.23, 0.65) |
<0.001 |
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.
Government: | NHLBI |
Quality Criteria Checklist: Primary Research
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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 | |