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HTN: Diet Patterns (2015)

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

To compare the effects on BP and vascular compliance of a low sodium-DASH, low-acid-load diet with reference to healthy diet in menopausal or post-menopausal women with BP levels at the upper end of the normal-range BP.

 

 

Inclusion Criteria:
  • Experiencing menopausal symptoms
  • Had passed through menopause and were not taking hormone replacement therapy
  • BMI between 16kg/m2 and 35kg/m2
  • Seated systolic blood pressure (SBP) 120mm Hg or more and less than 160mm Hg and diastolic blood pressure (DBP) 80mm Hg or more and less than 95mm Hg at screeening
  • A home SBP 116mm Hg or higher or DBP 78mm Hg or higher (using an average of seven days) before randomization
  • A clinical diagnosis of hypertension and taking anti-hypertensive medication/therapy (AHT).
Exclusion Criteria:
  • Low or normal BP
  • Experienced menopause before turning 43 years old
  • Taking warfarin, diphenylhydantoin or medications for osteoporosis treatment such as biphosphonates
  • Had been treated for cancer within the past three years
  • Had a cardiovascular event in the past six months
  • Had insulin-dependent diabetes
  • Consumed more than 30 standard alcoholic drinks per week
  • Ate main meals outside the home more than twice per week.
Description of Study Protocol:

Recruitment

The subjects were recruited from the general community.

Design

Randomized parallel dietary intervention.

Intervention

  • Subjects were randomly assigned one of the diet groups: 
    • Vitality (VD): DASH-type diet low-dietary-acid load that contained 100g of cooked red meat per week and maximum of four servings of bread and cereals
    • Reference Healthy Diet (RHD) consisting of general dietary guidelines to reduce fat intake and increase intake of breads and cereals (minimum of four servings per day) for 14 weeks 
    • Both diets were designed to provide adequate calcium (1,000mg per day), with at least three servings per day of low-fat milk and dairy products, but the VD subjects were asked to restrict their cheese consumption because of its high sodium content
    • Usual energy recommendations were provided, but it was significantly different in dietary acid load because of the increase in the bread and cereal load and a 19mEq per day potential renal acid load (PRAL) or 12mEq per day net endogenous acid production (NEAP)
    • Both groups were given the recommendation to consume monounsaturated margarine or polyunsaturated margarine and cooking oil with adjustments to meet energy requirements
    • All the dietary instruction was provided by a RD
    • The participants were seen on weeks two, four, eight, 12 and 14 and had telephone contact at weeks six and 10.

Statistical Analysis

  • Statistical analyses were performed using SPSS version 14.0 with results represented as means ± SEM
  • Randomization was stratified by BMI and use of AHT
  • Differences between the two diets at baseline or during the intervention period were assessed using Student T-tests
  • Paired T-tests were performed to assess changes in outcome variables from baseline to the end of the study, or changes from baseline to the intervention period
  • Analysis of variance (ANOVA) with repeated measurements was used to compare the changes in BP and urinary electrolyte excretion over the 14-week study period between the two diets, and stepwise multiple linear regression analysis was used to identify predictors of BP changes
  •  An X2-test was performed to evaluate significant differences in proportions of subjects between the two diet groups
  • All differences were considered significant if P<0.05.
Data Collection Summary:
Dependent Variables
  • Systolic blood pressure and diastolic blood pressure: Left arm with automated TM2551 after five minutes of seated rest. Four measurements, one minute apart, were taken and average of the last three were used.
  • Urinary electrolyte excretion: Two 24-hour urine collection, run-in period and four times (four, eight, 12, 14 weeks). Urinary sodium, potassium, calcium, magnesium, phosphate, creatinine and urea concentrations measured using a Randox Daytona.
  • Serum lipids: Overnight fasting blood samples were collected at baseline and at weeks eight, 12 and 14 with a Hitachi 704 analyzer.     
  • Anthropometrics and body composition: Baseline and 14 weeks:
    • Weight: Digital scale with light clothing and no shoes
    • Height: Stadiometer
    • Waist, hip circumference: Measured to nearest centimeter
    • Total body fat: Dual energy x-ray absorptiometery.
Independent Variables
  • Vitality diet (VD): Low-sodium DASH-type diet with low dietary acid load containing six servings of 100g cooked lean red meat per week
  • Reference healthy diet (RHD): Based on general dietary guidelines to reduce fat intake and increase intake of breads and cereals.

 

Description of Actual Data Sample:

Initial N

N=111 women aged between 45 and 75 years.

Attrition (Final N)

  • VD: N=53  (start); final N=46 (reason subjects left the study include six that chose not to commit and one with an illness or  family issues) 
  • RHD: N=58 (start); final N=49 (reason subjects left the study include six that chose not to commit and three with illness or family issues).

Age

  • VD: Average of 60±0.7 years
  • RHD: Average 58.4±0.7 years (P=0.12 for differences between groups).

Anthropometrics

 
Anthropometric Characteristics (Mean ± SEM) of Subjects at Baseline
 
Parameter VD (N=46) RHD (N=49) P-value for Group Difference
Weight (kg) 78.0+2.0 79.0+1.7 0.71
Height (cm) 162.6+1.0 163.1+0.9 0.72

BMI (kg/m2)

 29.5+0.7 29.7+4.2 0.79
Waist circumference (cm) 97.5+1.9 98.2+1.6 0.79
Hip circumference (cm) 111.4+1.4 111.1+1.3 0.86
Systolic blood pressure (mm Hg) 128.3+1.6 126.9+1.4 0.52
Diastolic blood pressure (mm Hg) 80.7+1.1 81.3+0.9 0.67

 

Location

Australia.

 

Summary of Results:

Key Findings

  • Systolic blood pressure during the entire intervention was lower for the VD group as compared to the RHD (P=0.4)
  • The VD group had a decrease in SBP by  5.6±1.3 mm Hg (mean±SEM) compared with a fall of 2.7±1.0mm Hg in the RHD (group difference, P=0.08)
  • The change in DBP did not differ between groups
  • For those taking AHT, the VD group had a greater fall in both SBP and DBP compared to the ARHD group throughout the study (repeated-measures ANOVA time by diet, both P<0.05)
  • After 14 weeks of intervention, the VD group (N=17) had a significant fall of SBP (6.5±2.5mm Hg, P=0.02) and of DBP (4.6±1.4mm Hg, P=0.005), which was greater than that of the RHD group (N=18), by 5.2±2.8mm Hg SBP (group difference, P=0.08) and 3.5±1.7mm Hg DBP (P=0.05)
  • Both groups had small reductions in body weight (NS between groups):
    • VD: 1.1±0.3kg (P=0.001)
    • RHD: 0.8±0.3kg (P=0.01).
  • Weight loss explained 7%  of the variance of SBP reduction (P=0.01) and 6% of DBP reduction (P=0.02); a 1kg weight loss was associated with a fall of 1.0±0.4mm Hg SBP (P=0.005) and 0.6±0.3mm Hg DB (P=0.02) with age, body weight at baseline, weight loss and change in urinary sodium included in the model
  • Among  subjects on AHT, a reduction in urinary sodium predicted the fall in DBP (9% variance, P=0.07) after adjustment
  • Dietary acid load as measured by PRAL and NEAP was not predictive of  BP responses observed in the VD or RHD group
  • There was a significant difference between the groups in sodium and potassium content with a lower sodium and higher potassium excretion in the VD group as compared to the RHD
  • VD, a low-sodium DASH diet with the inclusion of lean red meat on most days of the week, with a low-acid load was more effective in reducing BP in free-living post-menopausal women compared to the RHD, which was a high-carbohydrate, low-fat diet with a higher acid load
  • There was a decrease in spot urine pH in the RHD group
  • This effect was stronger those taking AHT
  • Data from food records and diaries also reflected good compliance with the dietary recommendations.
Author Conclusion:

A low-sodium DASH diet, with lean red meat on most days of the week, and low-acid load is more effective in reducing BP in older women as compared to the high-carbohydrate, low-fat diet with a higher acid load, and this effect was greater in those with AHT.

 

Funding Source:
Other: meat and livestock of Australia
In-Kind support reported by Industry: Yes
Reviewer Comments:

The reviewer agrees with the authors conclusions. The strength of the study was the randomization that led to non-significant differences between the groups. The diet was designed to maintain body weight, which it did.

 

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")? Yes
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? Yes
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? ???
  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? ???
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? 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? Yes
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