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Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet]. York (UK): Centre for Reviews and Dissemination (UK); 1995-.

Database of Abstracts of Reviews of Effects (DARE): Quality-assessed Reviews [Internet].

Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials

D Mozaffarian, R Micha, and S Wallace.

Review published: 2010.

CRD summary

This review concluded that consuming a diet containing polyunsaturated fatty acids instead of saturated fatty acid reduced coronary heart disease events. The search strategy may have excluded relevant studies, data came from older studies (1968 to 1992) and quality appeared generally low. The conclusions should be treated with caution.

Authors' objectives

To assess the impact on coronary heart disease endpoints of increased polyunsaturated fatty acid consumption as replacement for saturated fatty acids.

Searching

MEDLINE, EMBASE, AGRIS, AMED, HMIC, PsycINFO, The Cochrane Library, Web of Knowledge, CABI, CINAHL, ZETOC, Faculty of 1000 Medicine and SIGLE were searched to June 2009. Search terms were reported. Reference lists and related articles were checked and experts contacted. No language restrictions were applied.

Study selection

Randomised controlled trials (RCTs) of at least one year that compared increased total or n-6 polyunsaturated fatty acid consumption without other major concomitant interventions to control diet as primary or secondary prevention in adults were eligible for inclusion. The outcomes of interest were coronary heart disease events (myocardial infarction, coronary heart disease death, sudden death). Studies that assessed mainly n-3 polyunsaturated fatty acid interventions were excluded.

Participants in the included studies were institutionalised men and women with or without coronary heart disease or men with recent or prior myocardial infarction or established coronary heart disease. The interventions were provided meals (feeding trials) or dietary advice, or a mixture of these. Dietary assessment was by direct analysis of provided foods, diet records, questionnaires and interviews. Polyunsaturated fatty acid intake ranged from 8.0% to 20.7% energy in the intervention group and from 4.0% to 6.4% energy in the control group.

One reviewer initially reviewed titles and abstracts. Two reviewers independently assessed full papers for inclusion. Differences were resolved by group consultation and consensus.

Assessment of study quality

Quality was assessed using the Jadad scale of randomisation, blinding and withdrawals/dropouts. The maximum score was 5. Scores of 0 to 2 were considered of lower quality and 3 to 5 as higher quality.

Study quality was assessed by two reviewers independently. Differences were resolved by consensus.

Data extraction

The numbers and types of first coronary heart disease events during follow-up were extracted. Where necessary, standard errors were calculated. Risk ratio (RR) and 95% confidence intervals (CI) were calculated. Authors were contacted to clarify information.

Data were extracted independently by two reviewers. Disagreements were resolved by consensus.

Methods of synthesis

Pooled risk ratios and 95% CI were calculated using DerSimonian & Laird random-effects model. Heterogeneity was assessed using Q and I2 statistics. Stratified meta-analyses and meta-regression were used to investigate any effect of trial duration (< or ≥ median for all trials), study population (primary versus secondary prevention) and quality score (0 to 2, 3 to 5). Subgroup analyses were undertaken based on enrolment design (trials with open enrolment excluded and cluster randomisation), extent of blinding, type of dietary intervention (provision of meals, dietary advice).

Publication bias was investigated using a funnel plot and Begg's test.

Results of the review

Eight RCTs (13,614 participants) were included. Study size ranged from 55 to 9,057 participants. Two studies were cluster RCTs (818 participants) where hospitals were the unit of randomisation and participants joined on hospitalisation and left on discharge, others were parallel studies. Four trials evaluated secondary prevention, three evaluated primary prevention and one evaluated mixed population. Date of publication ranged from 1968 to 1992. Follow-up ranged from an average of one year to eight years. Funnel plot showed potential for publication bias and Begg's test was borderline. Two studies (9,903 participants) scored 3 for quality and six (3,711 participants) scored 2.

Compared to control, risk of coronary heart disease events was reduced with polyunsaturated fatty acid diet (RR 0.81, 95% CI 0.70 to 0.95, I2=37%).

In subgroup analyses, the result was similar to the main analysis for longer term studies, secondary prevention and studies that scored 2 for quality.

Risk of coronary heart disease mortality was reduced with polyunsaturated fatty acid diet (RR 0.80, 95% CI 0.65 to 0.98). There was no effect on total mortality.

In sensitivity analyses, coronary heart disease events were reduced with polyunsaturated fatty acid diet in analyses that excluded studies with open enrolment and those studies that assessed dietary advice. Restriction to double blind trials and to studies that provided meals showed no statistically difference between polyunsaturated fatty acid and control in risk of coronary heart disease events.

Authors' conclusions

Consuming polyunsaturated fatty acids instead of saturated fatty acids reduced coronary heart disease events.

CRD commentary

The aims of the review were clearly stated in terms of participants, intervention and study design. A wide range of sources was searched and no language restrictions were applied, which should have reduced the risk of publication bias. However, the search terms used (and the way they were combined, in particular specific exclusion of studies that contained certain words) meant that relevant studies may have been missed. The authors' tests showed a potential for publication bias. Methods of study selection, data extraction and quality assessment were those likely to reduce risks of reviewer error and bias. Quality was assessed using a scoring system. Full details for individual studies were not presented, so it was difficult to comment on the reliability of data presented; however, the authors reported that most studies were of lower quality. It was unclear whether the methods of synthesis were appropriate as it appeared that no account was taken for inclusion of data from cluster randomised trials. Heterogeneity was investigated appropriately. Details of the participants and the intervention and control diets in the included studies were limited. The included data came from older studies (published between 1968 and 1992) and it was likely that dietary habits changed considerably over time.

One of the authors stated that he received funding from GlaxoSmithKline, Sigma Tau and Pronova to fund trials of fish oil.

As relevant studies may have been excluded by the search and data came mainly from older studies of apparent lower quality, the authors' conclusions should be treated with caution.

Implications of the review for practice and research

Practice: The authors stated that recommendations to reduce saturated fatty acids should specify the importance of replacement with polyunsaturated fatty acids. Recommendations for an upper limit of polyunsaturated fatty acid consumption at 10% energy needed to be revisited.

Research: The authors stated that future trials should investigate other dietary interventions, such as increased polyunsaturated fatty acid consumption to replace carbohydrate and replacing saturated fatty acids with carbohydrate or monounsaturated fatty acids.

Funding

National Heart Lung and Blood Institute NIH (R01-HL-085710-01); Searle Scholar Award, from the Searle Funds at the Chicago Community Trust.

Bibliographic details

Mozaffarian D, Micha R, Wallace S. Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLOS Medicine 2010; 7(3):e1000252. [PMC free article: PMC2843598] [PubMed: 20351774]

Indexing Status

Subject indexing assigned by NLM

MeSH

Coronary Disease /pathology; Dietary Fats /pharmacology; Fatty Acids /pharmacology; Fatty Acids, Unsaturated /pharmacology; Feeding Behavior /drug effects; Humans; Meta-Analysis as Topic; Randomized Controlled Trials as Topic

AccessionNumber

12010003077

Database entry date

09/02/2011

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.

CRD has determined that this article meets the DARE scientific quality criteria for a systematic review.

Copyright © 2014 University of York.

PMID: 20351774

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