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Some healthy vegetable oils may actually increase the risk of heart disease, new research shows.

The findings suggest it may be time to reconsider cholesterol-lowering claims on some food labels, says Richard Bazinet of the department of nutritional sciences at the University of Toronto.

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“This is important information for people buying certain foods because of the heart benefits when really, that’s not accurate,” he says. “While most of these foods are a good choice, there are a few notable exceptions.”

The study, published in the Canadian Medical Association Journal, reports that replacing saturated animal fats with polyunsaturated vegetable oils has become common practice for consumers, based on the understanding that they reduce serum cholesterol levels and help prevent heart disease.

Since 2012, Health Canada’s Food Directorate has allowed the food industry to use a label on the oils—and foods containing them—claiming “a reduced risk of heart disease by lowering blood cholesterol levels.”

“Healthy” isn’t so simple

But the new research shows it’s more complicated than the label suggests—and the problem lies in the ratio of two kinds of polyunsaturates fatty acids found in the oils.

“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 omega-3 α-linolenic acid may not be warranted,” write Bazinet and Michael Chu, Lawson Health Research Institute and Division of Cardiac Surgery at Western University in London, Ontario.

Corn and safflower oil, which are rich in omega-6 linoleic acid but contain almost no omega-3 α-linolenic acid, are not associated with beneficial effects on heart health, Bazinet says.

The authors cite a study published earlier this year in February in which “…the intervention group replaced saturated fat with sources of safflower oil or safflower oil margarine (rich in omega-6 linoleic acid but low in omega-3 α-linoleic acid).

“They found that the intervention group had serum cholesterol levels that were significantly decreased (by about 8 percent to 13 percent) relative to baseline and the control group, which is consistent with the health claim.”

However, rates of death from all causes of cardiovascular disease and coronary artery disease significantly increased in the treatment group.

“When the new results were added to a meta-analysis, the net result was a borderline 33 percent increase in heart disease risk for oils rich in omega-6 and poor in omega-3, with absolutely no evidence of a benefit as is implied by the health claim,” Bazinet says.

“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,” the study concludes.

Source: University of Toronto