Some vegetable oils previously believed to offer health benefits may in fact increase the risk of heart disease, says a new Canadian report.

According to an analysis of recent research published Monday in the Canadian Medical Association Journal, vegetable oils high in omega-6 linoleic acid but low in omega-3 a-linolenic acid, such as corn and safflower oil, appear to lower cholesterol levels. However, these oils were also associated with higher rates of death from cardiovascular disease and coronary artery disease.

The report’s authors cite research published in February 2013 that included a group of subjects that replaced saturated fat in their diets with sources of safflower oil or safflower oil margarine. The study found that this group had cholesterol levels between eight and 13 per cent lower than when they began the study and compared to the control group. But the death rates from cardiovascular and coronary artery disease also “significantly increased” in this group.

The report’s authors note that in 2009, Health Canada’s Food Directorate approved a request from the food industry to put labels on products with vegetable oils that say they offer “a reduced risk of heart disease by lowering blood cholesterol levels.” Health Canada made this decision after reviewing published studies that found polyunsaturated vegetable oils reduce serum cholesterol levels and help prevent heart disease.

But given the new research, the report’s authors recommend that Health Canada reconsider those labelling guidelines.

"Careful evaluation of recent evidence suggests that allowing a health claim for vegetable oils rich in omega-6 linoleic acid but relatively poor in omega-3 a-linolenic acid may not be warranted," the authors -- Dr. Richard Bazinet from the University of Toronto and Dr. Michael Chu from Western University -- conclude.

The Vegetable Oil Industry of Canada (VOIC) responded to the report by saying it was based on “a new analysis of old data” and included subjects with a history of cardiovascular disease.

“That study's participants, men with a history of cardiovascular disease, were tested with very high doses of Omega-6 at 15 per cent of daily energy, which is more than three times the intake level of Canadians,” the VOIC said in a statement to CTV News.

“There is a substantial body of evidence supporting a recently approved health claim in Canada advising consumers to replace dietary sources of saturated fat with polyunsaturated and monounsaturated fats from vegetable oil to lower cholesterol.” 

That drop in cholesterol, the agency says, reduces the risk of heart disease.

Dietitian Rosie Schwartz says high cholesterol levels are not the only risk factor for heart disease. Schwartz told CTV that other risk factors include inflammation of the arteries, which is where omega 3 can have a protective effect.

According to Schwartz, what consumers must understand about the latest findings is that they need to ensure their diet includes both omega 6 and omega 3 fatty acids.

When choosing oils, she said, extra virgin olive oil and canola oil are best.

“If we keep consuming too much in the way of omega 6s, we are looking at higher heart disease rates,” she said.

“Omega 3s are anti-inflammatory and Omega 6 are inflammatory. They balance each other out. So we need more anti-inflammatory oils in our diet.”

With files from CTV News medical specialist Avis Favaro and Elizabeth St. Philip