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HTN: Diet Patterns (2015)

Citation:

Epstein DE, Sherwood A, Smith PJ, Craighead L, Caccia C, Lin PH, Babyak MA, Johnson JJ, Hinderliter A, Blumenthal JA. Determinants and consequences of adherence to the dietary approaches to Stop Hypertension Diet in African-American and white adults with high blood pressure: Results from the ENCORE trial. J Acad Nutr Diet. 2012; 112(11): 1,763-1,773.

PubMed ID: 23000025
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To determine what factors predict dietary adherence and the extent to which dietary adherence is necessary to produce clinically meaningful blood pressure reductions.
Inclusion Criteria:
  • Sedentary, overweight and obese adults (BMI 25kg/m2 to 39.9kg/m2)
  • Optimal blood pressure (SBP 130mm Hg to 159mm Hg or DBP 85mm Hg to 99mm Hg)
  • Provided written informed consent.
Exclusion Criteria:
Not described.
Description of Study Protocol:

Recruitment

Participants were recruited from the ENCORE trial (Exercise and Nutrition Interventions for Cardiovascular Health).

Design

Randomized controlled trial; ancillary study of the ENCORE trial (secondary analysis).

Intervention 

Patients were randomized to one of three groups:
  • DASH diet alone
  • DASH plus weight management
  • Usual diet (control).

Statistical Analysis

  • General linear models were used to compare treatment groups on post-treatment adherence to the DASH diet
  • Linear regression was used to examine potential predictors of post-treatment DASH adherence
  • Analysis of covariance was used to examine the relation of adherence to the DASH diet and BP.
Data Collection Summary:

Timing of Measurements

  • Cardio-respiratory fitness was measured using a modified Blake protocol in which workloads were increased at a rate of one metabolic equivalent per minute. Participants also underwent a maximal graded exercise treadmill test in which workloads were increased at a rate of one metabolic equivalent per minute.
  • Dietary habits were assessed at baseline and 16 weeks post-randomization using a well-validated 114-item, self-administered retrospective food frequency questionnaire (FFQ)
  • A food diary was used to gather information about dietary habits, specifically macronutrients and caloric intake. Participants kept a detailed food record for four consecutive days. Data were analyzed using food processor SQL edition software.
  • Participants completed a battery of psychometric questionnaires including Beck Depression Inventory II, a 21-item, self-report measure assessing the presence and severity of depressive symptoms.

Dependent Variables

  • Blood pressure:
    • Blood pressure was read four times using a standard mercury sphygmomanometer and stethoscope to determine resting clinic BP
    • To assess blood pressure during the day, participants wore an Accutracker II ambulatory BP monitor that was programmed to record BP measurements four times per hour throughout the waking hours and two times per hour during sleep. The mean BP during the entire 24-hour monitoring period adjusted for posture was used for the present analysis.
  • Dietary adherence:
    • Composite index of adherence to the DASH diet and clinic BP: Dietary adherence was assessed using a scoring scheme adopted from Folsom and colleagues
    • A composite DASH score was generated using the sub-scores from 10 equally weighted food and nutrient components (i.e., grains, fruits, vegetables, nut, seeds and legumes, meat, dairy, fat, etc.).
Independent Variables
  • Blood pressure:
    • Diet (DASH, DASH+weight control, usual diet)
    • Dietary adherence.
  • Dietary adherence:
    • Demographics (age, sex, income, education, ethnicity) 
    • Baseline BMI
    • Psycho-social variables.
Description of Actual Data Sample:
  • Initial N: N=144 randomized (47 males, 97 females)
  • Attrition (final N): N=140 completed (46 completed DASH weight management, 46 completed DASH alone and 49 completed usual care)
  • Age: Mean age was 52±10 years
  • Ethnicity: N=56 African American and 88 White
  • Other relevant demographics: A total of 47% of participants had resting clinic blood pressure higher than 140mm Hg SBP or higher than 90mm Hg DBP
  • Anthropometrics: Mean BMI 33.1±3.9kg/m2.

 

Summary of Results:

Key Findings

  • Compared with BP reductions in Usual diet controls ( SBP: 3.4mm Hg; 95% CI: 0.4 to 6.5; DBP: 3.8mm Hg; 95% CI: 2.2 to 5.5), there were significant reductions in BP for participants in the DASH diet plus weight management (SBP: 16.1mm Hg; 95% CI: 13.0 to 19.2; DBP: 9.9mm Hg; 95% CI: 8.1 to 11.6) and in DASH diet alone (SBP: 11.2mm Hg; 95% CI: 8.1 to 14.3; DBP: 7.5mm Hg, 95% CI: 5.8 to 9.3) showed significant reductions in blood pressure in comparison with usual diet controls
  • Greater post-treatment consumption of DASH foods was noted in both the DASH diet alone (mean was 6.20; 95% CI: 5.83 to 6.57) and DASH diet plus weight management groups (mean was 6.23; 95% CI: 3.30 to 4.01; P<0.0001) and greater adherence to the DASH diet was associated with larger reductions in clinic SBP and DBP (P<0.01)
    • Each two-point increase in DASH diet adherence was associated with a 3.4mm Hg (95% CI: 2.4mm Hg to 4.4mm Hg) reduction in SBP
    • Adherence did not significantly predict reduction in DBP after adjustment for weight loss
    • Higher levels of adherence to DASH diet were associated with larger clinic BP reductions (SBPmm Hg/DBPmm Hg): SBP: P<0.0001; DBP: P<0.004:
      • Quartile 1 (most adherent): 15.6/5.4mm Hg
      • Quartile 2: 13.4/8.3mm Hg
      • Quartile 3: 5.9/4.5mm Hg
      • Quartile 4: 5.2/6.0mm Hg.
    • Similar pattern for ambulatory BP (SBP/DBP mm Hg): SBP: P=0.024; DBP: P=0.002:
      • Quartile 1 (most adherent): 8.9/5.4mm Hg
      • Quartile 2: 5.2/2.8mm Hg
      • Quartile 3: 2.0/0.3mm Hg
      • Quartile 4: 0.4/-0.5mm Hg.
  • Only ethnicity predicted dietary adherence with African Americans less adherent to the DASH diet compared with whites (4.68; 95% CI: 4.34 to 5.03 vs. 5.83; 95% CI: 5.50 to 6.11; P<0.001).
Author Conclusion:
Greater adherence to the DASH diet was associated with a larger blood pressure reductions independent of weight loss. African Americans were less likely to be adherent to the DASH dietary eating plan compared with Whites, suggesting that culturally sensitive dietary strategies might be needed to improve adherence to the DASH diet.
Funding Source:
Government: National Heart Lung and Blood Institute Grant# HL074103
Other: General Clinical Research Center, National Institutes of Health (M01-RR-30)
Reviewer Comments:
It should be noted that the research volunteers in ENCORE were highly motivated, as evidenced by the very low dropout rate, suggesting that the entire study sample might not be fully representative of typical patients seeking treatment for high BP in clinical practice.
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? Yes
  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? 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.) No
  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? Yes
  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)? No
  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