HTN: Diet Patterns (2015)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To determine the effects of a Dietary Approaches to Stop Hypertension (DASH) eating plan on metabolic risks in patients with the metabolic syndrome.

Inclusion Criteria:

Have three or more of the following criteria to be diagnosed as having metabolic syndrome:

  • Abdominal adiposity: Waist circumference over 102cm in men or over 88cm in women
  • Low levels of serum HDL cholesterol: Under 40mg per dL in men or under 50mg per dL in women
  • Hypertriglyceridemia: Triacylglycerol level of at least 150mg per dL
  • Elevated blood pressure: At least 130/85mm Hg
  • Impaired glucose homeostasis: Fasting plasma glucose concentration of at least 110mg per dL.
Exclusion Criteria:
  • Patients with cardiovascular disease or psychiatric problems
  • Smokers
  • Took any medication affecting nutrient metabolism, blood lipids and blood pressure
  • Took any vitamin and mineral supplements and antacids containing magnesium or calcium.
Description of Study Protocol:


  • Recruited from among participants of the Tehran Lipid and Glucose study (TLGS)
  • All participants were residents of District 13 of Tehran. 


  • Randomized, controlled outpatient trial
  • The district was divided into three sub-areas, one of which was further away from the other two areas. This area was considered the case area, consisting of 5,000 subjects.
  • All people in the case area with serum lipid or glucose abnormalities or high blood pressure were invited to the diet therapy clinic. Those who accepted and had metabolic syndrome were randomly divided into two groups, DASH and Weight-Reducing. Subjects from the two other areas made up the Control Group, consuming a normal diet. The three diets were prescribed for six months.


Computer-generated random assignment to weight-reducing or DASH diet.

  • Weight-reducing diet: Given general oral and written information about healthy food choices and a diet 500kcal less than their caloric needs according to their weight
  • DASH diet: Prescribed a diet with 500kcal less than their caloric needs, which was increased in fruit, vegetables and low-fat dairy products and lower in saturated fat, total fat and cholesterol, more whole grains and less refined grains, sweets and red meat. 

Statistical Analysis

  • One-way ANOVA and X2 tests for differences between groups
  • Repeated-measurement ANOVA for women and Friedman's for men to compare data at baseline, three months and six months
  • Used the X2 test to compare the prevalence of metabolic syndrome between the DASH diet and weight-reducing diet.
Data Collection Summary:

Timing of Measurements

Baseline, three months and six months.

Dependent Variables

  • Anthropometric measurements: Weight, height, waist circumference
  • Glucose
  • Triglycerides
  • Cholesterol
  • Blood pressures.

Independent Variables

  • Assignment to control diet, weight-reducing diet emphasizing healthy food choices or the DASH diet with reduced calories and increased consumption of fruit, vegetables, low-fat dairy and whole grains and lower in saturated fat, total fat and cholesterol and restricted to 2,400mg sodium
  • Nutrition counseling by nutritionist
  • Monthly visit and phone contact with nutritionist daily
  • Behavioral and psychological counseling offered
  • Three-day food diaries were analyzed monthly
  • Attendance at meetings and monthly visits was recorded.
Description of Actual Data Sample:

Initial N

116 participants

  • 34 men
  • 82 women.

Attrition (Final N)



41±12.3 years of age.



Other Relevant Demographics

All residents of District 13 of Tehran.


  • BMI: 28.9±9.8kg/m2 in men and 31.4±10.8kg/m2 in women
  • Baseline characteristics of these participants did not differ across the three diet groups
  • Controls were matched with cases for confounder variables.


Tehran, Iran.

Summary of Results:


  Weight-Reducing  Statistical Significance 
  Baseline Three months  Six months   

Men [data in median (25th, 75th percentiles]:

Waist circumference (cm


105 (86, 117)


(85, 116) 


100 (84, 114) 

Weight (kg 86 (79, 92)  80
(74, 89) 
(68, 79) 
Triglycerides (mg per dL

(166,  225) 

(157, 216) 
SBP (mm Hg

(125, 159) 

(120, 149) 
(118, 147) 

Women (data in means ± SD):

Waist circumference (cm) 

95±16  93±16  91±15  P=0.04  
Weight (kg)  70±11  63±8  58±7  P=0.04 
Triglycerides (mg per dL)  229±50  220±51  216±48  P=0.04  
  DASH diet      P=0.03  


Waist circumference (cm) 


(83, 115) 


(79, 111) 


(76, 110) 

Weight (kg)  87
(78, 95) 
80 (75, 89)  71 (67, 78)  P=0.03  
HDL (mg per dL)  33
(24, 40) 
36 (28, 42)  40 (31, 46)  P=0.03  
Triglycerides (mg per dL)  203 (165, 221)  189
(154, 216) 
(150, 215) 
Fasting Blood Sugar (mg per dL)  97
(91, 110) 
(84, 107) 
(78, 103) 


Waist circumference (cm) 

95±17  93±17  90±16  P=0.04  
Weight (kg)  71±10  63±8  57±6  P=0.03  
HDL (mg per dL)  30±7  37±7  40±7  P=0.02  
Triglycerides (mg per dL)  231±49  221±49  217±48  P=0.04  
Fasting Blood Sugar (mg per dL)  96±22  110±35  106±34  P=0.04  

Other Findings

  • Blood pressure values also decreased significantly over six months for subjects on the DASH diet for both men and women
  • Significant change in the lipid profiles, systolic and diastolic blood pressure, weight and waist circumference in men and women on the DASH diet (P<0.001)
  • Significant change in triglycerides, systolic blood pressure and weight on the weight-reducing diet (P<0.05)
  • Renal outcomes were not reported.
Author Conclusion:

A DASH diet might be effective in reducing the metabolic risks. The related mechanisms need further study.

Funding Source:
University/Hospital: Endocrine Research Center, Shaheed Beheshti University of Medical Sciences, Tehran, Iran
Reviewer Comments:

Could not be blinded because the nutritionist had to know which diet regimen the subjects were on for diet counseling. Authors mentioned several limitations of the study including:

  • Inability to report the soluble and insoluble fiber intakes separately in different diet groups
  • No trans fatty acid analysis in their nutrient analysis software so could not report the trans fatty acid intake in the three groups separately
  • No data about the level of serum insulin
  • Food was not provided to subjects.
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? ???
  4.1. Were follow-up methods described and the same for all groups? ???
  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? N/A
  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? No
  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