Not All PUFAs Created Equal, Say Researchers

November 14, 2013

TORONTO, ON – Not all polyunsaturated fatty acids (PUFAs) are created equal, according to a new report, so simply replacing dietary saturated fats with polyunsaturated fatty acids might not be enough to lower the risk of heart disease[1].

In an analysis published November 11, 2013 in CMAJ, two researchers argue that to obtain the "heart benefits" of polyunsaturated fatty acids, the emphasis should be on α-linolenic acid, an omega-3 fatty acid, and not on linoleic acid, which is an omega-6 fatty acid.

Given their concerns, Dr Richard Bazinet (University of Toronto, ON) and Dr Michael Chu (Western University, London, ON) argue that a broad cholesterol-lowering health claim for omega-6 fatty acids be reexamined. "We suggest that the health claim be modified such that foods rich in omega-6 linoleic acid but poor in omega-3 α-linolenic acid be excluded," they write.

In 2009, Health Canada's Food Directorate allowed a claim for polyunsaturated fatty acids by stating that when they replace saturated fats in the diet, there is a statistically significant reduction in total- and LDL-cholesterol levels, and the result is a reduction in the risk of coronary heart disease.

New AHA/ACC/NHLBI Lifestyle Guidelines

Just this week the American College of Cardiology (ACC) and American Heart Association (AHA) published their new Guideline on Lifestyle Management to Reduce Cardiovascular Risk . In it, they recommend individuals consume just 5% to 6% of calories from saturated fat and also advise adults to reduce their calories from saturated fat to lower LDL-cholesterol levels.

The ACC/AHA guidelines, developed in conjunction with the National Heart, Lung, and Blood Institute, note that in controlled studies, for every 1% of saturated fat that is replaced by polyunsaturated fat, LDL cholesterol is lowered 1.8 mg/dL. Although the new guidelines do not distinguish between the type of polyunsaturated fatty acids, the guidelines, chaired by Dr Robert Eckel (University of Colorado, Denver), highlight the benefits of the Mediterranean diet, a diet that is high in omega-3 fatty acids, in certain populations for the reduction of blood pressure.

In a section called "Gaps in Evidence and Future Research Needs," the ACC/AHA expert panel notes there is a need for further study on the relative effects of polyunsaturated fatty acids, including omega-3 fatty acids, on lipids, inflammation, and cardiovascular disease risk factors.

Not All PUFAs Have Same Effect

In their report, the Canadians argue that the full effects of substituting saturated fats with vegetable oils rich in polyunsaturated fats are not entirely clear. In a review of the data, they state there is "doubt as to whether the protective effects can be attributed to linoleic acid."

In one meta-analysis examining the sources of fatty-acid composition, the risk of cardiovascular death and MI was 22% lower when oils with a mix of α-linolenic and linoleic acid were used. "However, the rates of nonfatal myocardial infarction and death from coronary artery disease were not significantly lower when oils made up mostly of linoleic acid but relatively low in α-linolenic acid were substituted," write Bazinet and Chu.

The research also showed that soybean oil, which contains a mix of α-linolenic and linoleic acids, had a protective effect against coronary heart disease, but corn and safflower oils, which are rich in linoleic acid, did not. Data from the Sydney Diet Heart Study (SDHS) also revealed that safflower oil lowered LDL-cholesterol levels 8% to 13% but was associated with an increased risk of cardiovascular mortality.

For this reason, oils rich in linoleic acid should not be grouped together with oils that contain a mix of α-linolenic and linoleic acids, state Bazinet and Chu. They agree that it is not entirely possible to draw strong conclusions from the published data and that the reasons why linoleic acid was associated with increased cardiovascular mortality in SDHS are unclear. Still, they urge Health Canada to separate the two polyunsaturated fatty acids.

Bazinet reports support from Bunge, Unilever, and Kraft Foods. Chu reports support from Medtronic, Edward Lifesciences, and NeoChord.

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