The meta-analysis of data from upcoming cohort studies, published in the American Heart Association’s journal Circulation, said the review revealed there was “robust evidence” for the association, despite inconsistent results of previous studies.
The researchers from the Harvard School of Public Health said the conclusions supported current recommendations for a general population to replace saturated fat with linoleic acid (LA), a polyunsaturated omega-6 fat found in vegetable oils, for primary prevention of coronary heart disease (CHD).
The results suggested a 5% of energy increase in LA intake which replaced energy gained from saturated fat may lower the risk of CHD events by 9% and the risk of CHD-related death by 13%. Similar results were seen when 5% of energy from carbohydrates was replaced with linoleic acid.
The researchers used MEDLINE and EMBASE databases to find 13 published and unpublished cohort studies reporting an association with dietary LA, amounting to a total of 310,602 participants and 12,479 CHD events.
Polyunsaturated fats like linoleic acid are found in nuts, seeds, fish, oils and vegetable-oil based spreads, while saturated fats are found in dairy and meat.
The researchers said recommendations to reduce LA in the diet were based on, “minimal direct evidence”.
“Because of multiple, potentially competing effects on many metabolic pathways, the effects of LA on heart disease risks are difficult to predict by these mechanistic considerations. A diet high in LA is considered to increase lipid susceptibility to free radical oxidation and lipid peroxidation that may play a role in etiology [cause] of cancer,” they wrote.
“However, in the extensive literature on this topic, including many prospective studies and meta analyse, there is little evidence that higher intake of LA is associated with an increased risk of cancer in prospective studies.”
The researchers said some studies suggested that n-6 polyunsaturated fatty acid - of which LA is the predominant form in western diets - alone increased the risk of CHD mortality. However, they dismissed these findings due to sample size and trial duration as well as the practice of partial hydrogenation of vegetable oils in special spreads back in the 1960s when these studies were conducted meaning the results may have been confused.
Concerning their own analysis, they acknowledged that the data used did not take into account brand names of any margarine, cooking oils and salad dressings that may contain LA, meaning intake levels may have been underestimated.
Published online ahead of print, doi: 10.1161/CIRCULATIONAHA.114.010236
“Dietary Linoleic Acid and Risk of Coronary Heart Disease: A Systematic Review and Meta-Analysis of Prospective Cohort Studies”
Authors: M. Farvid, M. Ding, A. Pan et al.