DF: Cardiovascular Disease (2008)

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

To determine whether a high-fiber diet would reduce inflammatory markers (e.g., CRP) and to compare results obtained using a diet naturally high in fiber with those obtained using a fiber supplement (Psyllium) to acheive the same amount of grams per day of fiber. 

Inclusion Criteria:
  • Lean, normotensive
  • 21 years to 49 years of age
  • BMI below 25
  • Waist-to-hip ratio less than 0.80 for women; less than 0.85 for men
  • BP below 130/85mmHg consistently on three visits prior to study
  • FBG below 110mg per dL
  • HbA1c below 5.6%
  • Fasting TGs under 125mg per dL
  • HDL over 40mg per dL for men; over 45mg per dL for women
  • Total cholesterol under 200mg per dL
  • Obese hypertensive (high to normal, Stage I hypertension)
  • BMI of 27 and greater, with three or more of the following:
    • Waist circumference over 40 inches for men, over 35 inches for women
    • BP in the range of 130/85mmHg to 159/99mmHg, consistently on three visits prior to the study
    • No medications, no diabetes
    • FBG under 126mg per dL; HbA1c under 7%
    • Fasting TG above 150mg per dL
    • HDL below 50mg per dL for women, below 40mg per dL for men.
Exclusion Criteria:
  • Diabetes mellitus (FBG at least 126mg per dL)
  • Clinically-evident target organ damage
  • Left ventricular hypertrophy (per ECG)
  • Serum creatinine at least 1.5mg per dL
  • Findings from urine protein dipstick test at least 0.1g per dL
  • History of stroke, transient ischemic attack, MI, angina pectoris or CHF
  • Pregnancy.
Description of Study Protocol:
  • Recruitment: MUSC from staff and clinics using newspaper and internet ads. Potential participants called the study coordinator, were screened over the phone and gave informed consent.
  • Design: A randomized crossover intervention trial of two diets. A diet naturally high in fiber vs. fiber supplement after a baseline diet for three weeks.
  • Blinding used (if applicable): None mentioned.

Intervention

Subjects consumed their baseline diet for three weeks and then were assigned to one of:

  • A diet naturally high in fiber (30g per day, DASH, also naturally high in antioxidants, potassium, magnesium, with more PUFA and MUFA and less saturated fat) 
  • A diet supplemented with psyllium fiber to reach 30g per day for three weeks each
  • The intervention diets (DASH and psyllium, plus supplementation of potassium and magnesium) were randomized in a two-period crossover design
  • Kcal was planned and regulated to acheieve diet composiiton of 50% CHO, 34% fat and 16% protein. 

Statistical Analysis

  • Before-after comparisons of all subjects in each diet group
  • T-tests to compare CRP between diet groups, fibrinogen and WBC
  • Two-period crossover ANOVA for CRP primary dietary analysis (using Satterwaite approximation for degrees of freedom). Crossover effect test performed at an alpha level of  0.10
  • Multivariate ANOVA to examine differences in CRP and fibrinogen levels and WBC between normo- and hypertensive subjects.
  • Statistical significance at P=0.05.
Data Collection Summary:

Timing of Measurements

  • First three weeks: Baseline diet
  • Next six weeks: Three weeks of DASH or psyllium supplementation for three weeks, then switched to other diet condition
  • In the third week during the intervention trial, all foods and drinks consumed were photographed for diet composition analysis and compliance
  • Urine was collected weekly to measure Na, K, Ca, Mg and compliance
  • Weight was measured weekly (those losing and gaining more than 1.4kg were excluded from the study).

Dependent Variables

  • Serum CRP (high-sensitivity CRP assay)
  • Fibrinogen (Clauss clotting method)
  • WBC (automated hematology).

Independent Variables

Fiber content.

Control Variables

  • Age
  • Race.
Description of Actual Data Sample:
  • Initial N: 35 (28 females, seven males; 18 lean or normotensive, 17 obese hypertensive)
  • Attrition (final N): 35
  • Age: 38.3±1.2
  • Ethnicity: 16 black, 21 white
  • BMI: 28.4±1.1
  • Systolic BP: 121±2.5
  • Diastolic BP: 76±1.9
  • Location: Medical University of South Carolina.
Summary of Results:

Variables

Baseline Diet

DASH Diet

Supplemented Diet Significance

Fiber Intake (g/d)

11.9±0.3

27.7±0.06 

26.3±0.4 
Not reported

K Intake (mg/d)

 1926±41.0

 3762±58.0

4054±49.0
Not reported
Mg Intake (mg/d)
210±4.2
451±8.1
400±7.2
Not reported
CRP, All Subjects (mg/L)
4.4±1.0
3.8±0.98
3.6±1.0

P=0.046 (DASH from baseline); P=0.03 supplemented from DASH

CRP, Lean (mg/L)
2.0±0.6 
1.4±0.4 
1.2±0.4 
P<0.05 

CRP, Obese (mg/L) 

7.2±1.8
6.5±1.8 
6.2±1.8
P>0.05 
Fibrinogen (g/dL)
3.11±0.12 
3.12±0.12 
3.17±0.12 
P>0.05
WBC (x103/L)
5.4±0.25
5.5±0.26 
5.6±0.25 
P>0.05

Other Findings

Compliance rates were 89% and 84% for DASH and supplemented diet, respectively. 

Author Conclusion:
  • A diet high in fiber (approximately 30g per day), whether acheieved naturally or through a supplement, can modestly reduce CRP levels
  • Findings indicate that modification of dietary fiber may be helpful in modulating inflammation to a certain degree.
Funding Source:
Reviewer Comments:

Underpowered: Information about physical activity during trial is absent.

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? 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%.) No
  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? No
  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.) 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? 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