Heart healthy oils no good

There’s now more evidence that casts doubt on the traditional “heart-healthy” practice of replacing butter and other saturated fats with corn oil and other vegetable oils high in linoleic acid.

The findings, reported in the British Medical Journal, suggest that using vegetable oils high in linoleic acid might be worse than using butter when it comes to preventing heart disease, though more research needs to be done on that front.

This latest evidence comes from an analysis of previously unpublished data of a large controlled trial conducted in Minnesota nearly 50 years ago, as well as a broader analysis of published data from similar trials of this dietary intervention.

The analyses show that interventions using linoleic acid–rich oils failed to reduce heart disease and overall mortality. In the Minnesota study, participants who had greater reduction in serum cholesterol had higher risk of death.

“Altogether, this research leads us to conclude that incomplete publication of important data has contributed to the overestimation of benefits — and the underestimation of potential risks — of replacing saturated fat with vegetable oils rich in linoleic acid,” says co-first author Daisy Zamora, a researcher in the psychiatry department at the UNC School of Medicine. Along with corn oil, linoleic acid-rich oils include safflower, soybean, sunflower oil and cottonseed oil.

The belief that replacing saturated fats with vegetable oils improves heart health dates back to the 1960s, when studies began to show that this dietary switch lowered blood cholesterol levels. Since then, some studies, including epidemiological and animal studies, have suggested that this intervention also reduces heart attack risk and related mortality.

In 2009, the American Heart Association reaffirmed its view that a diet low in saturated fat and moderately high (5-10 percent of daily calories) amounts of linoleic acid and other omega-6 unsaturated fatty acids probably benefits the heart.

However, randomised controlled trials — considered the gold standard for medical research — have never shown that linoleic acid–based dietary interventions reduce the risk of heart attacks or deaths.

The largest of these trials, the Minnesota Coronary Experiment (MCE), took place at the University of Minnesota between 1968 and 1973. It enrolled 9,423 patients. The investigators reported then that a switch to corn oil from butter and other saturated fats did lower cholesterol levels but made no difference in terms of heart attacks, deaths due to heart attacks, or overall deaths.