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HTN: Diet Patterns (2015)

Citation:

Al-Solaiman Y, Jesri A, Mountford WK, Lackland T, Ahao Y, Egan BM. DASH lowers blood pressure in obese hypertensives beyond potassium, magnesium and fiber. J Hum Hypertens. 2010: 24 (4): 237-246.

PubMed ID: 19626043
 
Study Design:
Randomized Crossover Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To separate the effects of minerals and fiber from other components of DASH on blood pressure and markers of endothelial and vascular function in abdominally obese pre-hypertensive and hypertensive patients with metabolic syndrome. 
Inclusion Criteria:
  • Lean normotensives:
    • Aged 21 years to 49 years
    • BMI less than 25kg/m2
    • Waist circumference less than 40 inches for men and less than 35 inches for women
    • Blood pressure (BP) consistently less than 130/85mm Hg on all three visits prior to first study
    • Fasting glucose (FG) less than 100mg per dL
    • Fasting triglycerides (TG) less than 125mg per dL
    • HDL-C 40mg per dL or higherl for men and 45mg per dL or more for women
    • TC less than 200mg per dL or TC/HDL 3.5 or less.
  • Abdominally obese:
    • BP of  130 to 159/85 to 99mm Hg on three screenings
    • Age 21 years to 49 years
    • Waist circumference more than 40 inches for men and more than 35 inches for women
    • At least one other metabolic syndrome criterion.
Exclusion Criteria:
  • Diabetes mellitus (FG 126mg per dL or more, or treatment)
  • Clinically evident target organ, or history of:
    • Stroke
    • Transient ischemic attack
    • Myocardial infarction
    • Angina pectoris
    • Chronic heart failure.
Description of Study Protocol:

Recruitment

Staff and clinics at Medical University of South Carolina.

Design

Randomized crossover trial.

Intervention

  • Standardized diet for three weeks with an average of one fruit and one vegetable (ULFV), approximately 1,700mg potassium (K), 250mg magnesium (Mg), 11g fiber, daily
  • Then they were randomized to ULFV supplemented with K, Mg and fiber (ULFV-S) to match DASH or DASH itself for three weeks. DASH was without additional low-fat dairy. 
  • Then subjects followed the complementary diet for three weeks
  • Nutrient target for the three diets was approximately 50% CHO, 35% fat and 15% protein, with 3,000mg sodium and 700mg calcium
  • Participants met individually weekly with the research RD who provided sample menus
  • Isocaloric energy intake was estimated using Harris Benedict equation.

Statistical Analysis

  • Group comparisons for categorical variables were made using Chi-square
  • For baseline variables, two-sample T-tests were used to compare obese and lean groups
  • One-sample T-tests were used to assess changes in nutritional variables between DASH and ULFV-S in obese hypertensives
  • Changes in BP, nutritional and biochemical measurements across the three dietary phases within and between groups were made using linear mixed models for repeated measures
  • An order effect of diet order on blood pressure was examined by Grizzle's method. 

 

Data Collection Summary:

Timing of Measurements

  • Weekly 24-hour urine collections
  • BP weekly during the first two weeks of the three study diets and after three weeks on each diet
  • Baseline blood and at end of each three-week diet period.

Dependent Variables

  • BP: Random-zero sphygmomanometer while seated
  • Small and large artery elasticity: HDI/Pulse Wave CR-2000
  • Aortic BP: Sphygmacor
  • Aortic augmentation index: Calculated
  • Plasma insulin: Radioimmunoassay
  • Homeostatic model assessment of insulin resistance (HOMAir) index: Calculated
  • Lipids: TG, TC and HDL-C were measured and LDL-C was calculated.

Independent Variables

Diet:
  • Weekly 24-hour urine collection
  • Three-day food records and digital photos of all food and beverages the three days before weekly visits with the RD.

Control Variables

Discontinuation of non-essential prescription and non-prescription medication and supplements at least weeks prior to starting study. Medications identified as essential and determined to have minimal effects on BP were allowed.

 

Description of Actual Data Sample:
  • Initial N: N=37 (seven males, 30 females)
  • Attrition (final N): N=30
  • Age: Ages 38.5±1.75 years
  • Ethnicity: A total of 16 White and 13 Black
  • Other relevant demographics: Age, gender and race were not different between the groups
  • Anthropometrics: Obese hypertensives had higher values than lean normotensives for BP, BMI, abdominal and hip circumferences, TG, FG and uric acid. 

 

Summary of Results:

Findings

  • Blood pressure:
    • Systolic blood pressure and diastolic blood pressure were lower in the obese after three weeks on DASH than either ULFV or ULFV-S
    • BPs were not different between ULFV and ULFV-S in the obese
    • Central systolic blood pressure and diastolic blood pressure were also lower in obese on DASH than ULFV but were not significantly different from ULFV-S
    • Brachial and central systolic blood pressure and diastolic blood pressure were not different among the three dietary periods in lean volunteers
    • No carryover effect was found of diet sequence on systolic blood pressure in lean normotensives, obese hypertensive or all subjects. 
  • Other:
    • Small and large artery elasticity values in obese hypertensives were higher on DASH than the other two diets, while values did not change significantly in lean normotensives. The aortic augmentation index was lower (improved) in both groups on DASH than ULFV-S. In obese hypertensives, this index was also lower on ULFV-S than the usual diet. 
    • Weight, heart rate, metabolic and urine electrolyte had no significant differences between DASH and ULFV-S in either lean normotensives or obese hypertensives except for a higher urine potassium and magnesium, which were higher on DASH and ULFV-S than ULFV diet.

 

Author Conclusion:
DASH is more effective than potassium, magnesium and fiber supplements for lowering blood pressure in obese hypertensives,which suggest that high fruits and vegetables DASH lowers blood pressure and improves endothelial function in this group by nutritional factors in addition to potassium, magnesium and fiber. 
Funding Source:
Government: National Institute of Health, National Center ofr Minority Health and Disparities, General Clinical Research Center
Reviewer Comments:
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? N/A
  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? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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.) N/A
  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? N/A
  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)? N/A
  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