• Increase Font Size
  • Decrease Font Size
  • View as PDF

DF: Cardiovascular Disease (2008)

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

To evaluate the impact of dietary fiber on markers of systemic inflammation and endothelial dysfunction in women with type 2 diabetes. 

Inclusion Criteria:

Sub-set of The Nurses' Health Study

  • Caucasian (over 95%)
  • Ages, 30 to 55
  • Self-reported diabetics, supplementary questionaire
  • Use National Diabetes Data Group criteria.
Exclusion Criteria:
  • History of the any of the following at the first blood draw between 1989 and 1990:
    • Myocardial infarction
    • Coronary artery bypass grafting
    • Percutaneous transluminal coronary angioplasty
    • Stroke.
Description of Study Protocol:

Recruitment

Analysis included women recruited and enrolled in the Nurses' Health Study in 1976.

Design

  • Cross-sectional analysis of data from 902 self-reported diabetic women enrolled in the Nurses' Health Study
  • Measurements of dietary intake were obtained in 1976, 1986 and 1990 using food-frequency questionnaires
  • Fiber intakes along with demographics, BMI, physical activity, menopausal status, hormone therapy and duration of diabetes were assessed from survey tool
  • Blood analysis was completed in 1989 and 1990 for inflammation and endothelial markers, C-reactive protein (CPR), tumor necrosis factor-a (TNF-R2), cellular cell adhesion molecule (1CAM)-1 and E-selectin.

Statistical Analysis

  • Linear regression model to evaluate the associations between the dietary variables and plasma concentrations of the inflammatory markers (used average intake of nutrients from the questionaires)
  • Dietary variables were analyzed in quintiles
  • Logrithmic transformation of non-normally distributed variables (Inflammatory markers)
  • Linear trend calculated by assigning median value for each quintile.
Data Collection Summary:

Timing of Measurements

  • Semi-quantitative food frequency: Administered twice (1986 and 1990)
  • Laboratory analysis: Administered once between 1989 and 1990.

Dependent Variables

  • Markers of inflamation
    • C-reactive protein (CPR)
    • Tumor necrosis factor-a receptor 2 (TNF)
    • Endothelial function
      • Soluble intracellular cell adhesion molecule (ICAM)-1
      • E-selectin.

Independent Variables

  • Dietary intakes; fiber
    • Total fiber
    • Whole grains
    • Germ
    • Bran
    • Glycemic load
    • Glycemic index.

Control Variables

  • Age
  • BMI
  • Alcohol consumption
  • Physical acitivity (MET per week)
  • Family history of coronary heart disease
  • History of hypertnesion or hypercholesterolemia
  • Oral diabetes medicaiton use
  • Insulin use
  • Post-menopausal status
  • Hormone use
  • Duration of diabetes
  • A1C.
Description of Actual Data Sample:
  • Initial N: 902 (no males, 902 females)
  • Attrition: N/A.

Age; Quintiles (Total Fiber)

  • Q1: Mean, 57 years
  • Q3: Mean, 58 years
  • Q5: Mean, 60 years.

Ethnicity

  • Caucasian: Over 95%
  • Other groups not listed.

Anthropometrics; Quintiles (Total Fiber)

  • Q1: 31
  • Q3: 30.1
  • Q5: 28.2 (significantly lower).

Other Demographics

Highest quintiles of whole grain and total fiber intake associated with significantly:

  • Lower BMI
  • Less alcohol intake
  • More physical activity
  • Less smoking.

Location

National Nurses' Health Study.

Summary of Results:

Age-Standardized Characterisitcs, According to Quintiles (Q) of Total Fiber and Whole-Grain Intakes

Variables

Q1

Q2

Q3

Q4

Q5

P-Value

Whole Grains

4.75

9.82

1.53

2.28

3.54

 

 

CRP

6.60

5.28

5.76

5.59

5.52

0.03

TNF

2,647

2,552

2,571

2,439

2,435

0.017

Bran

1.6

2.65

4.07

6.7

10.9

 

 

CRP

6.29

5.61

6.33

5.48

4.96

0.007

TNF

2,603

2,597

2,491

2,495

2,462

0.06

Glycemic Load

TNF

2,417

2,573

2,446

2,627

2,594

0.08

Glycemic Index

CRP

5.05

5.25

6.55

5.15

6.68

0.04

ICAM-1

307

296

310

322

331

0.07

TNF

2,387

2,397

2,620

2,583

2,660

0.0008

Inflammatory Markers

  • Whole grains
    • Associated with a decreased concentration of CRP (P=0.03) and TNF-R2 (P=0.01)
    • No effect on ICAM or E-selectin.
  • Germ
    • No effect on CRP, ICAM, E-selectin or TNF.
  • Bran
    • Associated with a decreased concentration of CRP (P=0.007)
    • No effect on ICAM, E-selectin.
  • Glycemic load
    • No effect on CRP, ICAM or E-selectin.
  • Glycemic index
    • Associated with a decreased concentration of CRP (P=0.04) and TNF-R2 (P=0.0008)
    • No effect on E-selectin.
Author Conclusion:
  • Increased intake of whole grains or low-glycemic index diet associated with lower markers of inflammation, as measured by CRP and TNF-R2
  • The effect of whole-grain, bran and cereal fiber were independent of dietary glycemic index and an additional mechanism may be involved
  • The authors recommend that patients with type 2 diabetes increase intake of whole-grain products and maintain a diet low in glycemic index.
Funding Source:
Government: NIH
Reviewer Comments:
  • This study showed an effect of dietary fiber, whole grains and bran in particular, on lower levels of CRP and TNF, but not the markers of endothelial function
  • Their data also suggests that glycemic index is related to increased inflammatory markers
  • The high subject number and good statistical analysis supports the roles of fiber and glycemic intake. 
  • Did not include data on current or historical glycemic control
  • Utilized data from FFQ.

 

 

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.) N/A
  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? Yes
  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? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  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? N/A
  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? No
  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? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  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? No
  6.6. Were extra or unplanned treatments described? No
  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? No
  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