Omega to 6 polyunsaturated fatty acids: Is a broad cholesterol to lowering health claim appropriate?

The replacement of dietary saturated fats with some, but not all polyunsaturated fatty acids reduces serum cholesterol levels and the risk of heart disease. New analyses suggest that replacing saturated animal fats with linoleic acid, an omega 6 polyunsaturated fatty acid, lowers serum cholesterol levels but increases the risk of death from coronary artery disease. Health Canada’s Food Directorate should reconsider the health claim that omega 6 polyunsaturated fatty acids reduce the risk of heart disease by lowering blood cholesterol levels. (Authors abstract)

Health Canada’s Food Directorate received a submission from industry requesting approval to use a claim of reduced disease risk on labels of vegetable oils and foods containing vegetable oils.  The health claim was related to the replacement of saturated animal fats with unsaturated fats, including polyunsaturated fatty acids, for “a reduced risk of heart disease by lowering
blood cholesterol levels. Health Canada’s Food Directorate reviewed the available published literature and concluded that, when saturated fats were replaced with polyunsaturated fatty acids, there was a statistically significant reduction in total and low to density lipoprotein (LDL) cholesterol, that the result was a reduction in the risk of coronary artery disease and that the therapeutic health claim was substantiated by scientific evidence and therefore was valid and “relevant to the Canadian population,” given nearly half of Canadians have hyperlipidemia. Careful evaluation of recent evidence, however, suggests that allowing a health claim for vegetable oils rich in omega 6 linoleic acid but relatively poor in  n3 a linolenic acid may not be warranted. The authors argue that it seems unlikely that the beneficial effects of vegetable oils can be attributed to linoleic acid.  Soybean oil (mixed linoleic and a linolenic acids;) was the most commonly substituted oil in the collective group of studies that showed a protective effect. Corn and safflower oil (oils rich in linoleic acid;), which contain virtually no a linolenic acid, were not associated with a benefit.  A test of heterogeneity between oils rich in linoleic acid and those containing mixed polyunsaturated fatty acids was statistically different for nonfatal myocardial infarction and death from coronary artery disease.  This finding supports the idea that oils rich in linoleic acid should not be grouped with those containing mixed polyunsaturated fatty acids. 
Was it the  n3 alpha  linoleic acid in the oils with mixed polyunsaturated fatty acids that was protective against death from cardiovascular disease? Despite the limitations of recent studies, it seems unlikely, however, that additional secondary analyses or new interpretations of these datasets will lead to the conclusion that increasing intake of omega 6 linoleic acid will decrease the risk of death from coronary artery disease.

In summary, much confusion has arisen from the lack of reporting of food sources in prospective cohorts. Data from prospective cohort studies and randomized controlled trials generally support the replacement of saturated fats with mixed polyunsaturated fatty acids to reduce the risk of death from coronary artery disease. However, it is unclear whether oils rich in omega to 6 linoleic acid but low in n3 alpha linolenic acid also reduce this risk. The authors suggest that the health claim be modified such that foods rich in omega to 6 linoleic acid but poor in n3 alpha linolenic acid be excluded. Future research is needed to examine the dietary methodologies used to measure polyunsaturated fatty acid intakes in observational studies and the metabolism of polyunsaturated fatty acids, as well as their role in coronary artery disease and other diseases. (Editors comments)