Some “healthy” oils may not be as healthy as advertised. While corn and safflower oils may lower cholesterol, they may not protect against heart disease and, in fact, they may do more harm than good.
For years, safflower and corn oils have been regarded as healthy oils because they contain low levels of saturated fat, which is harmful to the heart. The American Heart Association has labeled corn and safflower as “good oils.”
A new Canadian report may change this view.
Researchers there have recently recommended that the food industry not advertise foods containing these oils as heart healthy. Although safflower and corn oils may lower cholesterol levels, researchers have found that these oils may not protect against heart disease and may even increase heart disease risk.
Richard Bazinet, MD, of the Department of Nutritional Sciences at the University of Toronto, and Michael Chu, MD, with Lawson Health Research Institute and the Division of Cardiac Surgery at Western University in London, Ontario, cowrote this analysis.
These researchers highlighted results from an evaluation of recovered data from the Sydney Diet Heart Study, which followed people who replaced saturated fat with safflower oil or safflower oil margarine.
That research involved 458 men aged 30 to 59 years who had recently had a coronary event, such as a heart attack or an episode of angina (chest pain resulting from a lack of blood flow to the heart).
One group of participants were directed to reduce saturated fats (from animal fats, common margarines and shortenings) to less than 10 percent of energy intake and to increase linoleic acid (from safflower oil and safflower oil polyunsaturated margarine) to 15 percent of energy intake. Safflower oil is a concentrated source of omega-6 linoleic acid and but low in omega-3 a-linolenic acid.
The control group received no specific dietary advice. Both groups had regular assessments and completed food diaries for an average of 39 months. All non-dietary aspects of the study were designed to be equal in both groups.
The results showed that, compared with the control group, the omega-6 linoleic acid group had a higher risk of death from all causes (17.6 versus 11.8 percent) as well as from cardiovascular disease and coronary heart disease (17 vs. 11 percent).
Compared to the control group, those in the safflower group showed cholesterol levels that were 8 to 13 percent lower.
Based on other studies, however, Health Canada’s Food Directorate approved a request from the food industry in 2009 to allow labeling suggesting that vegetable oils rich in omega-6 linoleic acid but relatively poor in omega-3 a-linolenic acid, and foods containing these oils, offer "a reduced risk of heart disease by lowering blood cholesterol level.”
Products that may contain corn and safflower oils include mayonnaise, creamy dressings, margarine, chips and nuts.
After weighing this new evidence, Drs. Bazinet and Chu are urging Health Canada to reconsider those labeling 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 wrote.
Canola and soybean oils, on the other hand, contain both linoleic and α-linolenic acids and may be more heart healthy options, but further investigation is needed.
"While this is not the first analysis showing corn oil's deleterious effects on cardiovascular health, it is the first one I know of that summarizes all the omega-6 oils' effects on both cardiovascular health and all-cause morbidity and mortality," said Deborah Gordon, MD, a family physician and dailyRx Contributing Expert.
"As a physician who emphasizes traditional, nutrient-dense foods, I have always cautioned patients against consuming highly processed, omega-6 rich vegetable and seed oils. Despite recent research findings showing that saturated fats and cholesterol do not increase cardiovascular disease, we need other studies such as this one, showing that the modern oils we have substituted for butter and lard do not help us and indeed may harm us," said Dr. Gordon.
"And besides, who wouldn't rather eat their eggs gently fried in butter than in corn oil?" she said.
This study was published on November 11 in the Canadian Medical Association Journal. Dr. Bazinet has received research funding from Bunge Ltd.