Date Published: March 23, 2010
Publisher: Public Library of Science
Author(s): Dariush Mozaffarian, Renata Micha, Sarah Wallace, Martijn B. Katan
Abstract: Dariush Mozaffarian and colleagues conduct a systematic review and meta-analysis to investigate the effect of consuming polyunsaturated fats in place of saturated fats for lowering the risk of coronary heart disease.
Partial Text: Reduction in saturated fatty acid (SFA) consumption is traditionally a major focus of dietary recommendations to reduce coronary heart disease (CHD) risk. However, effects of such a strategy on clinical CHD events are surprisingly poorly established in both randomized controlled trials (RCTs) – and prospective cohort studies . Prior meta-analyses of RCTs have either studied the effects of very heterogeneous dietary fat interventions on very heterogeneous combinations of cardiovascular outcomes , or studied effects of dietary fat interventions on intermediate risk markers, such as blood lipids . Furthermore, although dietary guidelines often recommend reduction in SFA consumption, such guidelines often do not highlight any specific nutrient as preferable for replacing SFA in the diet –, implying that any macronutrient replacement (unsaturated fats, carbohydrate, or protein) will produce similar effects.
We followed the Quality of Reporting of Meta-analyses (QUOROM – now PRISMA (http://www.prisma-statement.org/))  guidelines throughout the design, implementation, analysis, and reporting of this meta-analysis (see Text S1 for PRISMA Statement).
The identified RCTs included a total of 1,042 CHD events among 13,614 participants (Table 1) –,–. Average PUFA consumption ranged from 4.0%E to 6.4%E (weighted mean 5.0%E) in the control groups and from 8.0%E to 20.7%E (weighted mean 14.9%E) in the intervention groups. Diet was assessed in the majority of trials by either direct analysis of provided foods or by multiple-day weighed diet records. Four trials evaluated secondary prevention populations, three trials evaluated primary prevention populations, and one trial evaluated a mixed population of individuals with and without established CHD. Many of the trials had design limitations, such as single-blinding, inclusion of electrocardiographically defined clinical endpoints, or open enrollment. All trials utilized blinded endpoint assessment. Quality scores were in the modest range and relatively homogeneous: all trials had quality scores of either 2 or 3. Combining all trials, the pooled risk reduction for CHD events was 19% (RR = 0.81, 95% CI 0.70–0.95, p = 0.008) (Figure 2). Statistical evidence for substantial between-study heterogeneity was not present (Q-statistic p = 0.13; I2 = 37%). In evaluating potential for publication bias, the trial by Watts et al.  was clearly a potential outlier both in terms of sample size and risk reduction. Excluding this trial, there was little change in the overall pooled result: RR = 0.82, 95% CI 0.70–0.95; p heterogeneity = 0.11, I2 = 42%. Visual inspection of the resulting funnel plot indicated some potential for publication bias (Figure S1), with a borderline Begg’s test (continuity corrected p = 0.07), although such determinations are limited when the number of studies is relatively small.
In this meta-analysis of RCTs, increasing PUFA consumption as a replacement for SFA reduced the occurrence of CHD events by 19%; each 5%E greater PUFA consumption reduced CHD risk by 10%. Whereas nearly all these trials were insufficiently powered to detect a significant effect individually, the pooled results demonstrate a significant benefit of replacing PUFA for SFA on clinical CHD events. Thus, this is only the second dietary intervention, together with consumption of long-chain omega-3 fatty acids (fish oil) ,–, that has now been clearly demonstrated to reduce cardiovascular events in RCTs.