Association of Dietary, Circulating, and Supplement Fatty Acids with Coronary Risk A Systematic Review and Meta analysis

Background Guidelines advocate changes in fatty acid consumption to promote cardiovascular health. Purpose To summarize evidence about associations between fatty acids and coronary disease. Data Sources MEDLINE, Science Citation Index, and Cochrane Central Register of Controlled Trials through July 2013. Study Selection Prospective, observational studies and randomized, controlled trials. Data Extraction Investigators extracted data about study characteristics and assessed study biases. Data Synthesis There were 32 observational studies (530 525 participants) of fatty acids from dietary intake; 17 observational studies (25 721 participants) of fatty acid biomarkers; and 27 randomized, controlled trials (103 052 participants) of fatty acid supplementation.  In observational studies, relative risks for coronary disease were 1.02 (95 per cent  CI, 0.97 to 1.07) for saturated, 0.99 (CI, 0.89 to 1.09) for monounsaturated, 0.93 (CI, 0.84 to 1.02) for long chain  3 polyunsaturated, 1.01 (CI, 0.96 to 1.07) for 6 polyunsaturated, and 1.16 (CI, 1.06 to 1.27) for trans fatty acids when the top and bottom thirds of baseline dietary fatty acid intake were compared. Corresponding estimates for circulating fatty acids were 1.06 (CI, 0.86 to 1.30), 1.06 (CI, 0.97 to 1.17), 0.84 (CI, 0.63 to 1.11), 0.94 (CI, 0.84 to 1.06), and 1.05 (CI, 0.76 to 1.44), respectively. There was heterogeneity of the associations among individual circulating fatty acids and coronary disease. In randomized, controlled trials, relative risks for coronary disease were 0.97 (CI, 0.69 to 1.36) for alpha linolenic, 0.94 (CI, 0.86 to 1.03) for long chain n3 polyunsaturated, and 0.89 (CI, 0.71 to 1.12) for  6 polyunsaturated fatty acid supplementations. Limitation Potential biases from preferential publication and selective reporting. Conclusion Current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats. (Authors abstract)

This study included a systematic review and meta analysis of data from long term prospective observational studies of a broad range of both dietary and biomarker fatty acid measures in coronary disease. To put the observational evidence into context, associations with coronary outcomes in the randomized trials of fatty acid supplementation were examined.  The findings do not support cardiovascular guidelines that promote high consumption of long chain 3 and 6 and polyunsaturated fatty acids and suggest reduced consumption of total saturated fatty acids. Statistically non significant associations in prospective studies of coronary disease that involved assessment of dietary intake of long chain 3 and 6 polyunsaturated fatty acids and heterogeneity of the associations between specific circulating long chain 3 and 6 polyunsaturated fatty acid composition and coronary disease were reported. The meta analysis of randomized trials of long chain 3 and 6 polyunsaturated fatty acid supplements suggests that supplementation with these nutrients does not statistically significantly reduce the risk for coronary outcomes. The review provides a comprehensive systematic synthesis of available evidence by including data from different sources of evidence and quantifies the risk for coronary disease for a wide range of individual fatty acid isomers and several relevant subgroups in a consistent way.  Limitations include the moderate amount of available data on some specific circulating fatty acids and possible overestimations of associations because of preferential publication of extreme findings or, analogously, by selective reporting of results for particular fatty acids with striking associations. Although selective reporting seems minimal among randomized trials, few observational studies reported on all measured circulating fatty acids. Therefore, selective underreporting may have contributed at least in part to the observational findings in this meta analysis.  In conclusion, the pattern of findings from this analysis did not yield clearly supportive evidence for current cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of saturated fats. (Editors comments)