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HTN: Diet Patterns (2015)

Citation:

Blumenthal JA, Babyak JA, Sherwood A, Craighead L, Pao-HWa L, Johnson J, Watkins LL, Wang JT, Kuhn C, Feinglos M, Hinderliter A. The effects of the dash diet alone and in combination with exercise and caloric restriction on insulin sensitivity and lipids. Hypertension. 2010; 55(5): 1,199-1,205.

 

PubMed ID: 20212264
 
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 the independent and combined effects of the DASH diet and weight loss plus exercise on biomarkers of cardiovascular disease risk (insulin sensitivity and lipids).

Inclusion Criteria:
  • Age 35 or greater
  • BMI 25 to 40kg/m2
  • Not taking anti-hypertensive medications
  • Sedentary
  • SBP 130 to 159mm Hg (averaged over four screening visits)
  • DBP 85 to 99mm Hg (averaged over four screening visits)
  • No co-morbidities that would preclude safe participation (e.g., diabetes requiring insulin or oral hypoglycemic agents).
Exclusion Criteria:
  • Under age 35
  • BMI less than 25 or greater than 40kg/m2
  • Taking anti-hypertensive medications
  • Engaging in regular exercise (non-sedentary)
  • SBP under 130 or over 159mm Hg (averaged over four screening visits)
  • DBP under 85 or over 99mm Hg (averaged over four screening visits)
  • Presence of co-morbidities that would preclude safe participation (e.g., diabetes requiring insulin or oral hypoglycemic agents).

 

Description of Study Protocol:
  • Reported results were part of the ENCORE trial
  • At baseline, the following were determined:
    • Blood pressure
    • Insulin sensitivity (QUICKI)
    • Glucose tolerance (OGTT)
    • Lipid profiles (HDL, LDL, VLDL, TGs)
    • Body weight
    • Body composition
    • Dietary and nutritional content
    • Fitness
    • Expired air
  • Subjects were randomized to DASH, DASH with a weight management program or to control for four months
  • At four months, measurements were repeated. For the control group, weight and BP were measured biweekly.

Location

Duke University Medical Center, US. 

Data Collection Summary:

Dietary Assessment Method

  • Dietary intake was assessed by two self-reports, a retrospective FFQ (recall of consumption over four weeks) and a four-day diary
  • The FFQ was analyzed by NutritionQuest; the diary data was analyzed by Food Processor SWL edition software. 

Description of Dietary Interventions/dietary Patterns Identified in the Study

  • Dietary intervention was the DASH diet, which is rich in fruits, vegetables, fiber and low-fat dairy, and low in fat.
  • Diets provided were isocaloric diet for DASH-only treatment, and a 500kcal deficit for weight management
  • After two weeks of controlled feeding, participants were instructed to maintain their assigned diets. 

Outcomes Measured

All baseline measurements were repeated at four months:

  • Blood pressure
  • Insulin sensitivity (QUICKI)
  • Glucose tolerance (OGTT)
  • Lipid profiles (HDL, LDL, VLDL, TGs)
  • Body weight
  • Body composition
  • Dietary and nutritional content
  • Fitness
  • Expired air.

Methods of Outcome Assessment

  • BP: Average of four BP screening visits, standardized for cuff size, position, environment and time of day
  • Insulin sensitivity: QUICKI and the Insulin Sensitivity Index
  • Glucose tolerance: OGTT using a load of 75g; measures of plasma glucose by Beckman auto-analyzer at zero, 30, 60, 90 and 120 minutes; insulin measured at zero and 120 minutes
  • HDL, LDL, VLDL and TGs: Obtained from fasting blood samples drawn between 8:00 a.m. and 9:00 a.m.; assays were measured enzymatically
  • Body weight: Standard balance scale; participants in light clothing without shoes
  • Body composition and fat distribution: DEXA
  • Dietary and nutritional content: Retrospective FFQ, food diary; analyzed by NutritionQuest and Food Processor SQL Edition, respectively
  • Fitness: Maximal-graded exercise treadmill test with workloads increased at one metabolic equivalent per minute
  • Expired air: Collected by mouthpiece for quantification of minute ventilation, oxygen consumption and carbon dioxide production with a Parvo Medics True One measurement system.

Description of Actual Data Sample:
  • Sample size:
    • Initial N:
      • DASH-weight management: 49
      • DASH-only: 46
      • Control: 49
      • Total: 144
    • Final N:
      • DASH-weight management: 46 completed, 46 with complete OGTT, 49 used in intent-to-treat analysis
      • DASH-only: 46 completed, 44 with complete OGTT, 46 used in intent-to-treat analysis
      • Control: 48 completed, 48 with complete OGTT, 49 used in intent-to-treat analysis
      • Total: 140
      • Attrition: four (2.8%); three from DASH-weight  management, one from Control 
  • Age, mean (SD): 52.0 (10)
  • Gender, percent (N): Female, 67% (97)
  • Race/ethnicity, percent (N):
    • Caucasian: 60% (86)
    • African American: 39% (56)
    • Asian: 1% (2)
  • Baseline weight status, mean (SD): 93.1kg; BMI 33.1 (3.9) (overweight is an inclusion criterion)
  • Baseline distribution of dietary patterns: Not reported; reports only adherence data to dietary protocols
  • Education, percent (N):
    • High school: 34% (49)
    • Some college: 11% (15)
    • Completed college: 22% (32)
    • Post-graduate school: 24% (34)
    • Other: 9% (13).
Summary of Results:

Overall Results

  • Adherence to protocol was excellent
  • Mean post-treatment weight, percent body fat and trunk fat were significantly lower in the DASH-WM group
  • Lean body mass was lower in the DASH-WM group compared to other groups
  • DASH-only (-A) did not differ from the control on any body composition measure
  • Aerobic fitness: Mean post-treatment peak VO2 max was higher in DASH-WM compared to DASH-A and control (P<0.001). Participants in the DASH-WM group showed a 19% increase in VO2 max comapred to a non-significant decrease in DASH -A and control.
  • Improvements in glucose response were greater in the DASH-WM compared to other groups
  • DASH-WM had significantly lower total cholesterol and TGs compared to other groups. DASH-A was not different from other groups other than a marginally lower HDL compared to the control.
  • Values are mean and 95% confidence interval. Values after treatment are adjusted for pretreatment levels of outcome variable, age, gender, and ethnicity. P-values are adjusted using Tukey’s Honestly Significant Difference procedure.

 

    Treatment Group (Mean and 95% CI) P-value from Pairwise Comparison After Treatment
Variable   DASH-WM DASH-Ad Control DASH-WM vs. DASH-A DASH-WM vs. Control DASH-A vs. Control
Total % body fat Before

37.6 (35.5, 39.7) 

45.4 (33.2, 37.5)

36.4 (34.3, 38.5)

 <0.001  <0.001  0.293 
  After

33.1 (32.4, 33.8)

36.2 (35.5, 36.8)

36.9 (36.2, 37.6)

      
Total LBM (kg)  Before

56.0 (53.0, 59.1) 

57.5 (54.2, 60.7)

56.7 (53.7, 59.8)

 <0.001  <0.001  0.694 
  After

54.3 (53.8, 54.9)

56.8 (56.2, 57.4)

56.5 (55.9, 57.0)

      
Total trunk fat (kg)  Before

17.7 (16.4, 19.0)

 16.2 (14.9, 17.5)
16.9 (15.6, 18.2)
 <0.001  <0.001  0.217 
  After

13.6 (13.1, 14.1)

16.2 (14.9, 17.5)

17.1 (16.7, 17.6)

      
Fasting glucose (mg per dL)  Before

89.4 (86.4, 92.3)

90.4 (87.3, 93.5)

91.3 (88.4, 94.3)

 0.324  0.006  0.214 
  After

87.2 (85.1, 89.3)

89.4 (87.3, 91.5)

 91.9 (89.9, 93.9)      
Fasting insulin (µU per ml)  Before 18.1 (15.7, 20.4) 16.6 (14.2, 19.0) 18.0 (15.7, 20.3)  <0.001 <0.001  0.711 
  After 12.5 (10.8, 14.3)

17.6 (15.9, 19.4)

 18.6 (16.9, 20.2)      
Glucose (AUC) (mg per dL minutes)  Before

6,057 (5,221, 6,893)

6,087 (5,224, 6,951)

6,345 (5,508, 7,181) 

 0.011  0.005  0.958 
  After

4,947 (4,340, 5,554)

6,087 (5,224, 6,951)

6,345 (5,508, 7,181)

      

ISI0.120 (mg · L2 per mmol · µU · minute)

 Before

74.4 (67.1, 81.8)

70.9 (63.5, 78.3)

66.0 (58.8, 73.2)

 0.031  0.026  0.981 
  After

75.3 (71.8, 78.8)

68.7 (65.1, 72.3)

68.8 (65.4, 72.2)

      
QUICKI  Before

0.319 (0.313, 0.325)

0.319 (0.313, 0.325)

0.315 (0.309, 0.321)

 <0.001  <0.001 0/859 
  After

0.334 (0.329, 0.339)

0.318 (0.313, 0.323)

0.316 (0.312, 0.321)

      
Total cholesterol  Before

209 (198, 220)

199 (188, 211)

206 (195, 217)

 0.008  <0.001  0.364 
  After

184 (177, 199)

199 (192, 205)

205 (199, 211)

      
LDL  Before

128 (118, 138)

122 (112, 132)

126 (116, 136)

 0.054  0.005  0.714 
  After

112 (106, 117)

122 (116, 127)

125 (119, 130)

      
HDL  Before

55 (50, 59)

53 (49, 57)

55 (51, 59)

 0.115  0.911  0.047 
  After

54 (52, 55)

51 (50, 53)

54 (53, 56)

      
TG  Before

133 (116, 149)

122 (106, 139)

122 (106, 139)

 <0.001  <0.001  0.900 
  After

93 (81, 106)

129 (117, 142)

130 (118, 142)

      

WM=weight management.

A=Alone.
 
 
Confounders
Total Energy Intake Physical Activity Baseline Weight Status Sex Age Smoking Other
  Sedentary is an inclusion criterion x (baseline weight) x x   Baseline value, gender, ethnicity

 

 

 

Author Conclusion:

While the DASH diet alone can reduce BP in overweight, sedentary adults with high BP, there was little evidence that the DASH diet improved insulin sensitivity or lipids without the addition of exercise and weight reduction. It appears that caloric consumption rather than nutrient composition is most salient for improved metabolic function.

Strengths and Limitations

  • Adherence to protocol was excellent
  • Because there was no difference in insulin sensitivity between groups randomized to the intervention with or without the DASH diet, and there was a trend towards greater weight loss in the DASH group,the added value of the DASH diet is uncertain
  • The study evaluates the DASH diet only but other diets could be beneficial
  • Could not determine the impact of exercise independent of weight loss.

Reviewer Comments:

None.

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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
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")? ???
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? ???
5. Was blinding used to prevent introduction of bias? ???
  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.) ???
  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? ???
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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
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
 
 

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