13 April 2016

Rachel Worsley

Consuming vegetable oils rich in linoleic acid lowers blood cholesterol but does not reduce deaths from heart disease, according to a study published in the BMJ.

US researchers analysed unpublished data recovered from a decades-old trial of more than 9000 people which tested whether replacing saturated fats with vegetable oil (corn oil) reduced cardiovascular (heart disease, stroke and blood vessel) deaths through the lowering of blood cholesterol.

People in the vegetable oil group did report lower cholesterol levels, but the researchers also found there was a 22% higher risk of death for each 0.8 mmol/L (30mg/dL) reduction in serum cholesterol levels.

And surprisingly, members of the vegetable oil group also did not have less fatty build up in the arteries (atherosclerosis) or fewer myocardial infarcts (signs of a heart attack) at autopsy compared with the group that consumed saturated fats.

The researchers conducted a systematic review of 4 other trials but failed to find any reduction in death from coronary heart disease or other causes through replacing saturated fats with vegetable oils.

They say the collective findings from the trials “do not provide support for the central diet-heart tenet that the serum cholesterol lowering effects of replacing saturated fat with linoleic acid translate to reduced risks of coronary heart disease and death”.

The researchers say the new findings add to growing evidence that “incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid”.

They say it’s possible key results from the trial were not published at the time because they were “clearly at odds with prevailing beliefs”.

“It is interesting to speculate whether complete publication of [. . .] results might have altered key policy decisions promoting replacement of saturated fat with linoleic-rich oils or contributed to a shift in research priorities,” the researchers write.

They suggest attention should now turn towards why high consumption of linoleic acids leads to higher mortality.

In a linked editorial, public health physician and researcher Dr Lennert Veerman, from the University of Queensland, says “the benefits of choosing polyunsaturated fat over saturated fat seem a little less certain than we thought”.

He pointed out the analysis is limited by its lack of generalisability beyond a nursing home cohort, and other confounders.

In the meantime, people should eat “more fish, fruits, vegetables and whole grains” and avoid salt, sugar, trans-fats and over-eating, he says.

Last Reviewed: 13/04/2016



BMJ 2016; online 12 April