Hypertension

HTN: Diet Patterns (2015)

Citation:

Nowson CA, Worsley A, Margerison C, Jorna MK, Godfrey SJ, Booth A. Blood pressure change with weight loss is affected by diet type in men. Am J Clin Nutr 2005;81:983-989.

PubMed ID: 15883419
 
Study Design:
Randomized Controlled Trial
Class:
A - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To determine the effect on blood pressure of a DASH-type weight-loss diet (WELL diet) and to compare this with usual low-fat dietary advice in free-living individuals who selected and prepared their own food.
Inclusion Criteria:
  • > 25 years old
  • Seated office blood pressure:
    • >= 120 mmHg systolic blood pressure (SBP)
    • OR >=80 mmHg diastolic blood pressure (DBP)
    • This was the mean of last 3 of 4 measurements, taken in 1-minute intervals
  • Patients on hypertensive medication as long as they agreed to continue current medication.
  • BMI between 25 and 35 kg/m2
Exclusion Criteria:
  • Had a cardiovascular event on the past 6 months
  • Had insulin dependent diabetes
  • On Warfarin or Phenytoin
  • Ate main meal outside the home >2xs/wk
  • Drank >30 standard alcohol drinks/wk (10 g alcohol)
  • Plans to change smoking habits
  • Unwilling to cease taking dietary supplements (including vitamins)
Description of Study Protocol:

Recruitment

Participants recruited by newspaper article advertisement, and through BP measurement sessions at workplaces and shopping centers.

  • Written informed consent provided
  • Consent form approved by the Deakin University Human Research Ethics Committee

Design:  Randomized clinical trial

Randomization

  • Subjects randomized to WELL diet (moderate-sodium, high-potassium, high-calcium, low-fast DASH diet) or to traditional low-fat diet
  • Performed by the chief investigator
  • Random number generator blocks of 8 (Excel, Microsoft Corporation, 2000)

Blinding Used (if applicable):  not possible - lab tests

Interventions:

Lifestyle Intervention

  • Goal Setting: >=1 Nutrition and >=1 Exercise goal for a total of 3 goals per visit
  • Intervention completed by a trained dietitian

Diet Interventions

  • Overseen by coordinating Dietitian
  • Education provided by trained research staff
  • Difference in the 2 interventions: WELL diet provided specific food group serving targets and the low fat diet did not.
  • Incentives for both groups:
    • Measuring cups and spoons
    • Individual feedback on daily intakes of fruits and vegetables
    • Dairy product of choice offered once in the study period
    • Feedback on the group’s progression provided graphically throughout the study
    • Subject could participate in a drawing to win a double movie pass
  • WELL diet (randomized diet 1)
    • Based on a modified US DASH diet
    • Recommendations:
      • Daily
        • >=4 servings fruit or fruit juice
        • >=4 servings vegetables
        • >=3 servings nonfat dairy products
        • limit fat to <=4 servings
      • Weekly:
        • >= 3 servings of fish
        • >= 1 serving legumes
        • >= 4 servings unsalted nuts and seeds
        • limit red meats to <=2 servings
      • Advised to avoid butter, added table/cooking salt, and salty foods; and to use poly- or mono- unsaturated margarine
    • Detailed diet booklet, recipes, and tips provided
  • Low-fat diet (randomized diet 2)
    • No specific diet targets/serving recommendations
    • Advised to limit or avoid:
      • High-energy foods and drinks
      • Saturated fat
      • Cheese and ice cream to twice per week
      • Foods fried in fat
    • Encouraged to choose:
      • Plant-based foods
      • Non-fat or reduced fat milk and yogurt
      • Lean meat
    • “Healthy Weight Guide” booklet (National Heart Foundation of Australia, 2002), recipes, and tips provided.

A maximum of 4 caffeine-containing drinks and 2 standard alcoholic drinks per day was allowed for both groups.

Physical Activity

  • All subjects required to participate in moderate-intensity exercise >=30 minutes on all or most days of the week.
  • “Be Active Everyday” (National Heart Foundation, 1999) provided.
  • Individual exercise goals set at each visit
  • Subjects advise to increase heart rate to 60-79% of their maximum heart rate and retain for 30 minutes each session.
  • CHAMPS questionnaire- monitored amount of walking
    • Baseline (for 4 weeks)
    • Average hours per week for intervention period

Statistical Analysis

Descriptive statistics and regression analysis

  • Means
  • Unpaired Student’s t tests
  • Two-factor repeated-measures analysis of variance (diet x time)
  • GLM univariate analysis of variance
  • P values of 0.05 significant
Data Collection Summary:

Timing of Measurements

Anthropometry and blood pressure (baseline & post-intervention).  Home blood pressure (daily).  Fasting (10 hour) blood samples at the end of each control diet and test diet period.

Dependent Variables

  • Home systolic blood pressure and diastolic blood pressure
    • Automated blood pressure monitor
    • Data downloaded directly via computer by research staff
    • Participants trained:
      • to correctly apply the cuff
      • alone at the same time each day
      • after a 5 minute rest in a quiet room
      • 3 measurements with a 1 minute interval
  • Blood samples analyzed for serum total cholesterol, HDL-cholesterol, and triglycerides
  • LDL-calculated with Friedewald equation
  • Height taken using wall-mounted stadiometer, weight on digital scale each visit (light clothing, no shoes), waist circumference (timing of measure not specified)

Independent Variables

  • Diet intervention
    • WELL diet
    • Low-fat diet
  • Diet assessment (baseline; weeks 2,4,8,12)
    • 24-hour diet records each fortnight on the day before their visit with study staff
      • Timing
        • Mean of two 24-hour records at baseline
        • Mean of four 24-hour records at weeks 2, 4, 8, and 12
      • Trained personnel verified records
      • Diet analysis program used: Food Works, Professional Edition, Version 3.02, Xyris Software
    • Food-Frequency Questionnaire
      • Usual intake of fruits, vegetables, and dairy products
      • Baseline and week 12
Description of Actual Data Sample:

Initial N:

  • 220 responded to advertisements
    • 165 were sent a screening questionnaire and invited to attend further screening.
    • 63 met inclusion criteria and continued with home baseline blood pressure measurements
  • n = 63 at start
    • 4 dropped in low-fat group; 5 dropped in WELL group
    • 8 found it too difficult to comply with study demands
    • 1 moved interstate

Attrition (final N): 54 all male subjects, 16% dropout rate

Age:  see below

Ethnicity:  not mentioned

Other relevant demographics:  see below

Anthropometrics:  There were statistically significant differences between groups regarding height, BMI and waist circumference.

Location: Australia

Characteristic

WELL diet group (n = 27)

Low-fat diet group (n = 27)

Age (years)

47.1 ± 10.3

48.8 ± 8.3

Height (cm)

172.5 ± 5.2

177.4 ± 5.3

BMI (kg/m2)

29.6 ± 2.3

31.2 ± 2.4

Waist circumference (cm)

102.8 ± 7.7

110.3 ± 6.7

Office SBP (mmHg)

136.4 ± 16.2

133.6 ± 9.7

Office DBP (mmHg)

88.0 ± 9.7

88.7 ± 6.0

Pulse (beats/min)

69.3 ± 12.3

73.2 ± 9.9

Adapted from Table 1 of article

Summary of Results:

Walking

  • Increased in both groups
  • No significant difference between groups, P < 0.01
  • Food-Frequency questionnaire
  • No significant difference at baseline between groups
  • Week 12
    • WELL had increased intake of dairy products, P = 0.001
    • WELL had increased intake of vegetables, P = 0.001
    • Fruit increased significantly in both groups from baseline, P = 0.001
    • No significant difference in fruit and vegetable intake between groups, P = 0.001

 24-hour food records

  • WELL group had greater reductions the low-fat group in:
    • Dietary fat
    • Percent energy from fat
    • Percent energy from saturated fat
    • Sodium
  • WELL group had greater increases than the low-fat group in:
    • Percent energy from protein
    • Percent energy from carbohydrate
    • Potassium
    • Calcium
    • Magnesium
    • Phosphorus

Weight and blood pressure

  • Weight decreased significantly in both groups by approx 5.0 kg, P = 0.001
  • Rate of weight loss and the effect did not differ between the two groups
  • Greater decrease in blood pressure in WELL group
    • SBP: 5.5 ± 1.9 mmHg; P = 0.006
    • DBP: 4.4 ± 1.2 mmHg; P = 0.001
  • Greater decrease in pulse rate in WELL group
    • -3.8 ± 1.6 beats/minute; P = 0.023
  • After adjusting for baseline blood pressure and weight, the difference in decreasing SBP and DBP remaining between groups.
  • Overall, a significant effect of diet in blood pressure
    • SBP: P = 0.006
    • DBP: P = 0.001
  • A 10% weight change was associated with a 7% decrease in SBP and DBP
  • An increase in total dairy product intake was associated with decreased DBP, P 0.011.
  • An increase in vegetable intake was associated with decreased DBP, P = 0.052.
Author Conclusion:
  1. Targeted dietary advice combined with advice to walk >= 30 minutes on most days of the week resulted in 5% weight loss, 8 mmHg decrease in SBP, and 5 mmHg decrease in DBP over 3 months.
  2. A lifestyle intervention that can be successfully implemented by obese or overweight individuals results in a greater decrease in blood pressure than usual dietary advice to reduce fat intake.
Funding Source:
Industry:
Dairy Research and Development Council
Reviewer Comments:

Difficult to distinguish if the effect of the results are more related to total diet intervention, fruits and vegetables alone, or the increased calcium alone. There were statistically significant differences between groups regarding height, BMI and waist circumference.  Authors note that power to detect differences in blood lipids between groups was low due to limited number of subjects.   16% dropout rate.

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? ???
  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? ???
  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? 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? ???
  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)? 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