DF: Cardiovascular Disease (2008)
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.
- 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.
- 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.
- 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.
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.
- 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.
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.
- 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.
Underpowered: Information about physical activity during trial is absent.
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%.) | 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 | |