Summary of Evidence
In our main meta-analyses, based on the five RCTs that provided LA-rich vegetable oil in place of SFA, we found no evidence for reductions in either CHD mortality or all-cause mortality. This conclusion was unchanged after sensitivity analyses that either 1) included RCTs that offered advice only or that, in addition to LA sources, also provided n-3 EPA and DHA, or 2) included composite or non-fatal endpoints. However, evidence of moderate heterogeneity weakens the conclusions we can make about the CHD mortality findings and their ability to translate into recommendations for the population. Exploratory analyses suggest that neither the between-group differences in serum cholesterol lowering nor the doses of LA provided help to explain this heterogeneity.
Limitations
The small number of RCTs that have tested the traditional diet-heart hypothesis replacing SFA with LA- rich vegetable oil is an important limitation of our meta-analysis. Remarkably, only five diet-heart RCTs have specifically tested whether provision of an LA-rich vegetable oil in place of SFA reduced risk of CHD death or all-cause mortality. The fact that the MCE accounted for about 80% of all randomized participants in these trials highlights the paucity of causal RCT evidence supporting the traditional diet heart hypothesis and the importance of the MCE in assessing the evidence base for LA-rich
interventions. Even with inclusion of advice-only RCTs (with only modest diet changes and other limitations) and RCTs confounded by provision of large quantities of n-3 EPA+DHA in sensitivity analyses, MCE still accounted for 68% of all randomized participants. The small number of RCTs, coupled with differences in methodological quality and design, and population characteristics of the individual RCTs (tables K and L) (reviewed in 13, 109) indicate that more research is needed in this area before evidence-based recommendations can be supported.
Conclusion
Available RCT evidence demonstrates that replacement of SFA with LA-rich vegetable oil effectively lowers serum cholesterol, but does not support the hypothesis that this translates to lower risk of death from CHD or all-causes.
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