According to the clinical trial, which has been published in the British Journal of Medicine, if you have heart disease, and replace your saturated animal fats with omega-6 polyunsaturated vegetable fats (PUFAs), you are actually more likely to die. Omega-6 linoleic acid is the most common dietary PUFA in Western diets, and can be found in safflower oil, corn oil, soybean oil, sunflower oil, and cottonseed oil.
Nutrition epidemiologist and study co-author, Daisy Zamora, PhD, commented, ‘These findings highlight the need to re-evaluate worldwide dietary advice to substitute omega 6 PUFAs for saturated fats.’ Dr Zamora is a postdoctoral researcher in the Programme on Integrative Medicine in the Department of Physical Medicine & Rehabilitation at the University Of North Carolina School Of Medicine.
Because data from the Sydney Diet Heart Study, which was a randomised controlled trial conducted from 1966 to 1973, was missing, it was not previously possible to carry out an in-depth analysis of the effects of linoleic acid on deaths from coronary heart disease and cardiovascular disease. However, as a team of researchers from the U.S. and Australia have been able to recover the original data from this trial, they have analysed the results using modern statistical methods to compare death rates from all causes, cardiovascular, and coronary heart disease.
In the original study, 458 men aged 30-59 years who had recently had a coronary event, such as a heart attack or an episode of angina, were randomly divided into two groups. Group one reduced their saturated fats (from animal fats, common margarines and shortenings) to less than 10% of their energy intake and to increase linoleic acid (from safflower oil and safflower oil polyunsaturated margarine) to 15%, whilst group two received no specific dietary advice.
The results showed 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. As this new data has been used to update an earlier meta-analysis (a review of all the evidence), and also showed no evidence of benefit, and suggested a possible increased risk of cardiovascular disease, current researchers say this emphasises a need to rethink mechanisms linking diet to heart disease.
According to the researchers, recovering the missing data ‘has filled a critical gap in the published literature archive’ which ‘could have important implications for worldwide dietary advice to substitute omega-6 linoleic acid (or polyunsaturated fatty acids in general) for saturated fatty acids.’