For several decades, substituting vegetable for animal fats has been the standard advice for preventing heart disease. But a new study published on the British Medical Journal website bmj.com suggests otherwise.
Vegetable oils are rich in polyunsaturated fatty acids (PUFAs), of which the most common in western diets is omega-6 linoleic acid.
British dietary recommendations are cautious about high intakes of omega-6 PUFAs, but some other health authorities, including the American Heart Association, have recently repeated advice to maintain, and even to increase, intake of omega-6 PUFAs.
However, the study says an in-depth analysis of the effects of linoleic acid on deaths from coronary heart disease and cardiovascular disease has not previously been possible because data from the Sydney Diet Heart Study — a randomized controlled trial conducted from 1966 to 1973 — was missing.
A team of researchers from the U.S. and Australia has recovered and analyzed the original data from this trial.
Their analysis involved 458 men aged 30-59 years who had recently had a coronary event.
Participants were randomly divided into two groups. The intervention group was instructed to reduce saturated fats (from animal fats, common margarines and shortenings) to less than 10 per cent of energy intake and to increase linoleic acid (from safflower oil and safflower oil polyunsaturated margarine) to 15 per cent of energy intake.
The results show that the omega-6 linoleic acid group had a higher risk of death from all causes, as well as from cardiovascular disease and coronary heart disease, compared with the control group.
In an accompanying editorial, Professor Philip Calder from the University of Southampton says the new analysis of these old data “provides important information about the impact of high intakes of omega-6 PUFAs, in particular linoleic acid, on cardiovascular mortality at a time when there is considerable debate on this question.”