HTN: Fiber (2007)
To compare the effect on BP of a low-sodium, high potassium diet (LNAHK) and a high-calcium (HC) to a dash-type diet (OD) in community-dwelling subjects who selected and prepared their own foods after given dietary advice.
- > 25 years old
- Office blood pressure measured by research staff at the center at their 2nd visit that was:
- >= 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
- OR a home blood pressure that was:
- >=116 mmHg SBP
- >=78 mmHg DBP
- This was a mean over 7days
- Partners of participants not otherwise eligible for study were entered into study to be helpful in maintaining dietary compliance.
- Patients on hypertensive medication as long as they agreed to continue current medication.
- Office blood pressure measured by research staff at the center at their 2nd visit that was:
- o >160 mmHg SBP
- o >90 mmHg DBP
- Had a cardiovascular event on the past 6 months
- Had insulin dependent diabetes
- On Warfarin or Dilantin
- 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)
Recruitment
Participants recruited by newspaper article advertisement. Also 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 Crossover Trial.
- Control diet between each test diet period to minimize interference with time-dependant reductions in blood pressure.
- 4 randomized groups, each to test 2 of the diets
- Group 1: Diet 1, DASH-type diet; Diet 2, LNAHK
- Group 2: Diet 1, LNAHK; Diet 2, DASH-type diet
- Group 3: Diet 1, DASH-type diet; Diet 2, high calcium diet
- Group 4: Diet 1, high calcium; Diet 2, DASH-type diet
- Trial time line
- 4 randomized groups, each to test 2 of the diets
1 week |
2 weeks |
4 weeks |
2 weeks |
4 weeks |
Run-in |
Control diet |
Diet one |
Control diet |
Diet two |
Control diet similar to DASH (Dietary Approaches to Stop Hypertension) trial control diet
- Low calcium, potassium and magnesium
- Presumed to be higher in this study because Australians eat more fruits and vegetables. Macronutrient profile and fiber similar to average Australian diet.
Randomization
- Subjects randomized to 1 of 4 groups (above)
- Performed by the chief investigator
- Random number generator blocks of 8 (Excel, Microsoft Corporation, 2000)
Blinding Used (if applicable): not possible - lab tests
Intervention (if applicable):
Control diet
- Low in calcium, magnesium, potassium
- Instructed to consume a maximum of the following daily:
- 1 serving dairy
- 1.5 servings fruit/fruit juice
- 3 servings vegetables
- limit potatoes to 3 servings
- limit tomatoes to 2 servings per week
- limit fish to 1 serving per week
- usual intake of fats and salt
Intervention diets
- DASH-type diet
- Based on U.S. DASH study
- High in potassium, magnesium, fiber; lower in saturated fat, sodium
- Advised to avoid butter, added table/cooking salt, and salty foods; and to use poly- or mono- unsaturated margarine (low sodium version provided)
- Recommendations:
- Daily:
- >= 3 servings of low fat dairy
- >= 8 servings of fruit and vegetables daily (3-4 fruit; 4-5 vegetables)
- Weekly:
- >= 3 servings of fish
- >= 1 serving legumes
- >= 4 servings unsalted nuts and seeds
- limit red meats to <=3 servings
- Daily:
- Low sodium high potassium diet (LNAHK)
- Lower in calcium and sodium
- No specific recommendations for dairy, fish, red meat, or use of poly-mono-unsaturated fats.
- Salt-free bread and margarine were provided
- Advised to avoid added table/cooking salt and salty foods
- Recommendations:
- Daily
- >=4 servings fruit
- >=5 servings vegetables
- Weekly
- >=2 servings legumes
- >=4 servings unsalted nuts and seeds
- Daily
- High calcium diet
- >= 4 servings of low-fat dairy products
- Maximum of 40g/day of reduced fat cheese
- No other dietary advice provided
Throughout all diet periods, subjects allowed a maximum of 4 caffeine-containing drinks and 2 standard alcoholic drinks per day.
Statistical Analysis
Descriptive statistics and regression analysis
- Means ± SD
- Used to describe the distribution of variables
- Means ± SEM
- Used when comparisons of group were made
- Change in blood pressure
- Subtracting mean value of test diet period from the mean value of the previous control diet period
- The difference in changes of blood pressure between test periods were analyzed with 2-tailed paired t tests
- P = 0.05 considered significant
- Multivariate regression analysis- to determine predictors of blood pressure change
Timing of Measurements
Weight, office blood pressure and dietary counseling every 2 weeks. Blood pressure taken daily during control diet period and taken daily during last 2 weeks of test diet period. 24-hour urine collections every 2 weeks (compliance) and fasting (10 hour) blood samples at the end of each control diet and test diet period.
Dependent Variables
- Home monitored blood pressure - 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
- Urine collections
- Blood samples analyzed for serum total cholesterol, HDL-cholesterol, and triglycerides
- LDL-calculated with Friedewald equation
- Height and weight
Independent Variables
- High calcium diet
- DASH-type diet
- Low sodium, high potassium diet
- Diet assessment
- 24-hour diet records every 2 weeks
- Trained personnel verified records
- Diet analysis program used: Food Works, Professional Edition, Version 3.02, Xyris Software
Control Variables
Initial N:
- Of those who responded, 348 were sent a screening questionnaire and invited to attend further screening.
- 118 met inclusion criteria and continued with blood pressure measurements
- 93 met blood pressure criteria and agreed to participate.
- 4 partners that did not meet blood pressure criteria were included (to increase compliance)
- n = 97 at start
- 3 men dropped before completion of test diet 1 (data not included)
- 2 women and 1 man dropped before completing test diet 2 (data was included for test diet 1 only)
- 4 stated inability to follow diet and 2 stated illness as reasons for dropping out
Attrition (final N): 94
Age: see below
Ethnicity: not mentioned
Other relevant demographics: see below
Anthropometry:
Location: Australia
Characteristic |
All subjects (n = 94) |
Antihypertensive medication (n = 42) |
No antihypertensive medication (n = 52 |
Women |
38 |
18 |
20 |
Men |
56 |
24 |
32 |
Age (years) |
55.6 ± 9.9 |
60.0 ± 7.3 |
52.1 ± 10.2 |
Weight (kg) |
84.0 ± 13.3 |
85.8 ± 13.3 |
82.6 ±13.3 |
BMI (kg/m2) |
29.0 ± 3.8 |
30.0 ± 3.8 |
28.2 ± 3.6 |
Home SBP (mmHg) |
129.4 ± 11.3 |
130.8 ± 10.7 |
128.3 ± 11.8 |
Home DBP (mmHg) |
80.6 ± 8.6 |
79.9 ± 9.0 |
81.1 ± 8.4 |
Pulse (beats/min) |
67.3 ± 8.5 |
67.7 ± 9.1 |
67.0 ± 8.2 |
Urinary sodium (mmol/d) |
149.9 ± 49.9 |
159.4 ± 48.8 |
142.1 ± 49.9 |
Urinary potassium (mmol/d) |
77.5 ± 24.5 |
79.4 ± 24.0 |
76.0 ± 25.0 |
Difference between control diet 1 and control diet 2 periods
- In the 2nd control diet, urinary potassium was 5.3 ± 2.4 mmol/d higher than the 1st (P < 0.05)
- In the 2nd control diet, home SBP was 1.3 ± 0.6 mmHg lower than the 1st (P < 0.05)
Dietary Intake
- DASH-type diet period compared to control diet had (P < 0.001)
- Higher
- Intake of energy (1.4 ± 0.2 MJ)
- Percentage of energy from protein (1.4 ± 0.4)
- Fiber (13.2 ± 1.0 g)
- Potassium (61.9 ± 3.4 mmol)
- Calcium (603.0 ± 42.4 mg)
- Magnesium (189.9 ± 14.0 mg)
- Phosphorus (622.4 ± 54.6 mg)
- Lower
- Fat (2.9 ± 0.8)
- Saturated fat (1.9 ± 6.3)
- Sodium (26.5 ± 4.9 mmol)
- Higher
- LNAHK diet compared to DASH-type diet had (test diet – control, P <0.05)
- Increased
- Fiber (+7 ± 3 g/d)
- Potassium (+21 ± 8 mmol/d)
- Decreased
- Sodium (–38 ± 11 mmol/d)
- Calcium (-287 ± 85 mg/d)
- Increased
- High calcium diet compared to DASH-type diet (P < 0.05)
- Increased
- Saturated fat (+7 ±3 g/d)
- Sodium (+49 ± 12 mmol/d)
- Calcium (+442 ± 77 mg/d)
- Lesser increase in
- Fiber (-9 ± 3 g/d)
- Potassium (-28 ± 5 mmol/d)
- Magnesium (-118 ± 24 mg/d)
- Increased
Blood pressure
From Table 4 of article:
|
Change in LNAHK – Change in DASH-type |
Change in high calcium – Change in DASH-type |
SBP, mmHg |
-3.5 ± 1.0 *** |
+3.1 ± 0.9 ** |
DBP, mmHg |
-1.9 ± 0.7 * |
+0.8 ± 0.6 |
Pulse, beats per minute |
-1.0 ± 0.7 |
+1.7 ± 0.8 * |
- Multiple regression analysis- pre-intervention home SBP [b = 0.11 (0.03)], pre-intervention home DBP [b = -0.97(0.04)], and difference in urinary sodium to potassium ratio [b = 1.98 (0.50)] together explain 40% of the variance (R2 = 0.40, P < 0.001) of the difference in home SBP between DASH-type and control diet periods.
Body weight
From Table 4 of article:
|
Change in LNAHK – Change in DASH-type |
Change in high calcium – Change in DASH-type |
Weight, kg |
-0.3 ± 0.2 |
+0.7 ± 0.2 (P < 0.01) |
- Compared with control diet, body weight in high calcium diet increased 0.9 ± 0.1 kg (P < 0.001).
- Compared with control diet, body weight in LNAHK diet decreased 0.4 ± 0.2 kg (P < 0.05).
- No change in body weight in DASH-type diet compared to control diet.
Serum lipids
Serum lipids did not change except HDL increased more in high calcium diet than DASH-type diet.
- Dietary education facilitated a healthier self-selection of foods and in turn improved blood pressure levels.
- A population-wide reduction in dietary sodium (through staple food), with an increase in potassium intake would be achievable and contribute to the maintenance of optimal blood pressure in the community
- A lower-sodium diet, high in fruits, vegetables, and dietary fiber, which is low in saturated fatty acids and includes low-fat dairy products and more fish is a valid recommendation for good health.
Industry: |
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Because urinary potassium was higher and SBP was lower, the question is raised if a 2-week control diet period is enough between the 4-week intervention periods. Good explanation of differing results from the U.S. DASH study.
Quality Criteria Checklist: Primary Research
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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? | 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? | 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)? | 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? | 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 | |