Whole Grain - CNPP

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

To review the current evidence from RCTs that assess relationship between the consumption of wholegrain foods and effects on CHD morality, morbidity and on risk factors for CHD in participants previously diagnosed with CHD or with existing risk factors for CHD. 

Inclusion Criteria:
  • RCTs that assessed effects of wholegrain foods or diets containing whole grains, over a minimum of four weeks, on CHD and risk factors
  • Adults with existing CHD or who had at least one risk factor for CHD (e.g., abnormal lipids, raised BP, overweight status).
Exclusion Criteria:
  • Multiple component interventions
  • Interventions that incorporated factors other than wholegrain foods and diets, unless effect of wholegrain foods and diets could be separated from other factors
  • Studies on foods based only on individual components of grain were not included (oat bran, wheat germ)
  • Studies examining effect of high-fiber diets, dietary fiber, cereal fiber, but where specific effect of wholegrain foods and diets could not be distinguished.
Description of Study Protocol:

Recruitment

MEDLINE, EMBASE, CINAHL, CENTRAL searches.

Design

  • Data extraction by two independent reviewers: General information, trial characteristics, intervention, participants, outcomes, results
  • Quality assessment: Cochrane criteria; method of randomization, concealment of allocation; blinding; intention-to-treat analysis.

Statistical Analysis

RevMan software:

  • Chi-squared  and I2 statistic tests for heterogeneity (P<0.01)
  • Pooling using weighted mean differences in fixed effects meta-analysis
  • Sensitivity analysis.

 

 

Data Collection Summary:

Dependent Variables

  • Total-C
  • LDL-C
  • HDL-C
  • TAGs
  • Body weight
  • CHD mortality, morbidity
  • Changes in risk factors.

Independent Variables

Whole grain foods and diets.

Control Variables

  • RCTs, concurrently-controlled trials included
  • Meta-analytic techniques
  • Study selection and inclusion in analysis.
Description of Actual Data Sample:
  • Initial N: N=92 potentially-relevant papers
  • Attrition (final N): N=10 studies included in the review.
Summary of Results:
  • Total-C: Eight out of nine studies reporting Total-C as outcome were based on oatmeal. Weighted mean difference was -0.19mmol per L (-0.30 to  -0.08, P=0.0005) for oatmeal diets vs. refined grain diets. Similar effect were seen from three studies providing data at six-week intervention (WMD = -0.23, -0.40 to -0.05, P=0.01), but not at four weeks. 
  • LDL-C: Eight out of nine studies reporting LDL-C as outcome were based on oatmeal. Weighted mean difference was -0.18mmol per L (-0.28 to -0.09, P<0.0001) for oatmeal vs. refined grain diets. Similar effect was seen from three studies providing data at six weeks of intervention (WMD = -0.25, -0.39 to -0.10, P=0.0008), but not at four weeks.
  • TAGs, HDL-C, body weight: No evidence of a difference in HDL-C on diets with oatmeal vs. refined grains from outcome data from pooling at four weeks, six weeks or all end-of-study data
  • Other outcomes: Insufficient evidence found to make any conclusions about effect of wholegrain on any other risk factors for CHD (FBG, insulin, insulin resistance, blood pressure). 
Author Conclusion:

There is some evidence from RCTs that wholegrain oats can reduce LDL-C and Total-C risk factors for CHD. There is a lack of trials on other wholegrain foods and diets. 

Funding Source:
Reviewer Comments:
  • See paper for data tables, search strategy
  • Studies included in the review included a variety of individuals
  • Authors state that the analysis was based on a limited number of studies and studies of poor quality. 
Quality Criteria Checklist: Review Articles
Relevance Questions
  1. Will the answer if true, have a direct bearing on the health of patients? Yes
  2. Is the outcome or topic something that patients/clients/population groups would care about? Yes
  3. Is the problem addressed in the review one that is relevant to dietetics practice? Yes
  4. Will the information, if true, require a change in practice? Yes
 
Validity Questions
  1. Was the question for the review clearly focused and appropriate? Yes
  2. Was the search strategy used to locate relevant studies comprehensive? Were the databases searched and the search termsused described? Yes
  3. Were explicit methods used to select studies to include in the review? Were inclusion/exclusion criteria specified andappropriate? Wereselectionmethods unbiased? Yes
  4. Was there an appraisal of the quality and validity of studies included in the review? Were appraisal methodsspecified,appropriate, andreproducible? Yes
  5. Were specific treatments/interventions/exposures described? Were treatments similar enough to be combined? Yes
  6. Was the outcome of interest clearly indicated? Were other potential harms and benefits considered? Yes
  7. Were processes for data abstraction, synthesis, and analysis described? Were they applied consistently acrossstudies and groups? Was thereappropriate use of qualitative and/or quantitative synthesis? Was variation in findings among studies analyzed? Were heterogeneity issued considered? If data from studies were aggregated for meta-analysis, was the procedure described? Yes
  8. Are the results clearly presented in narrative and/or quantitative terms? If summary statistics are used, are levels ofsignificance and/or confidence intervals included? Yes
  9. Are conclusions supported by results with biases and limitations taken into consideration? Are limitations ofthe review identified anddiscussed? Yes
  10. Was bias due to the review's funding or sponsorship unlikely? Yes