Br J Nutr. 2010 Dec;104(11):1586-600.
n-6 fatty acid-specific and mixed polyunsaturate dietary interventions have different effects on CHD risk: a meta-analysis of randomised controlled trials.
Section on Nutritional Neurosciences, Laboratory of Membrane Biochemistry and Biophysics, NIAAA, NIH, Bethesda, MD, USA. firstname.lastname@example.org
Randomised controlled trials (RCT) of mixed n-6 and n-3 PUFA diets, and meta-analyses of their CHD outcomes, have been considered decisive evidence in specifically advising consumption of ‘at least 5-10 % of energy as n-6 PUFA’. Here we (1) performed an extensive literature search and extracted detailed dietary and outcome data enabling a critical examination of all RCT that increased PUFA and reported relevant CHD outcomes; (2) determined if dietary interventions increased n-6 PUFA with specificity, or increased both n-3 and n-6 PUFA (i.e. mixed n-3/n-6 PUFA diets); (3) compared mixed n-3/n-6 PUFA to n-6 specific PUFA diets on relevant CHD outcomes in meta-analyses; (4) evaluated the potential confounding role of trans-fatty acids (TFA). n-3 PUFA intakes were increased substantially in four of eight datasets, and the n-6 PUFA linoleic acid was raised with specificity in four datasets. n-3 and n-6 PUFA replaced a combination of TFA and SFA in all eight datasets. For non-fatal myocardial infarction (MI)+CHD death, the pooled risk reduction for mixed n-3/n-6 PUFA diets was 22 % (risk ratio (RR) 0.78; 95 % CI 0.65, 0.93) compared to an increased risk of 13 % for n-6 specific PUFA diets (RR 1.13; 95 % CI 0.84, 1.53). Risk of non-fatal MI+CHD death was significantly higher in n-6 specific PUFA diets compared to mixed n-3/n-6 PUFA diets (P = 0.02). RCT that substituted n-6 PUFA for TFA and SFA without simultaneously increasing n-3 PUFA produced an increase in risk of death that approached statistical significance (RR 1.16; 95 % CI 0.95, 1.42). Advice to specifically increase n-6 PUFA intake, based on mixed n-3/n-6 RCT data, is unlikely to provide the intended benefits, and may actually increase the risks of CHD and death.
Americans were advised by the American Heart Association to increase their intake of omega-6 fatty acids found abundantly in margarines, mayonnaise, and salad dressings. Most of these foods are made with corn oil, soybean oil, and cottonseed oil (high in omega-6). This new meta-analysis found that when omega-6 was given to study participants, there was an increased risk of heart disease and death; cardiac death increased by 28% when compared to a mixed diet of omega-6 and omega-3 fats. Omega-3 fats are thought to be heart healthy. Analysis of the mixed diet studies resulted in a 8% risk reduction of death from all causes and a 22% reduction from heart disease death.
In 2009, the American Heart Association issued a news release which recommended “Omega-6 fatty acids: Make them a part of heart-healthy eating”. This apparently is not based on the research and many presently consider it flawed advice.
Bottom Line: Include omega-3 fats in your diet with more fish consumption (not fried) or with the use of fish oil supplements. Limit your intake of salad dressings, mayonnaise, and margarines made with these fats (read the labels and ingredient lists). Watch for more blog posts on this topic in the future.