Data shows high intake of omega-6 fatty acids is not advised for cardiovascular health

Research recently published in BMJ (British Medical Journal) examines accumulated data to reveal that advice given by the American Heart Association to increase consumption of omega-6 fatty acids, particularly linolenic acid found in corn, sunflower, safflower, and soybean oils, is misguided for cardiovascular health. The author of an accompanying editorial notes that linolenic acid...

"...is the most prevalent PUFA and omega 6 PUFA in most Western diets. As a result of the effects of linoleic acid on cholesterol concentrations, lowering intake of saturated fat and increasing that of PUFAs has been a cornerstone of dietary advice, with the aim of decreasing the risk of cardiovascular disease (CVD)."

Moreover...

"The American Heart Association recently repeated advice to maintain, and even to increase, intake of omega 6 PUFAs. This advice has caused some controversy, because evidence that linoleic acid lowers the risk of CVD is limited—most trials that claimed to investigate the effect of exchanging saturated fat for linoleic acid involved multiple dietary changes or multiple interventions (or both)."

As it turns out...

"The impact on CVD risk or mortality of replacing saturated fat with linoleic acid without changes in other fatty acids has rarely been investigated, and no large randomised controlled trial has recently explored this important question."

Therefore, in their paper the authors set out...

"...to evaluate the effectiveness of replacing dietary saturated fat with omega 6 linoleic acid, for the secondary prevention of coronary heart disease and death."

To do so they recovered data from the Sydney Diet Heart Study, a randomized controlled trial conducted in 1966-73 using 458 men aged 30-59 years with a recent coronary event (myocardial infarction, acute coronary insufficiency, or angina) as study subjects. In fact, death from cardiovascular disease specifically was not even reported in the original paper describing the Sydney Diet Heart Study. This updated meta-analysis included previously missing data. As described in the editorial:

"Participants were randomised to a diet rich in linoleic acid or continuation of their habitual diet. Both groups were treated the same in other respects and received the same advice. Baseline dietary intake data showed an average linoleic acid intake of about 6% of energy and an average saturated fatty acid intake of about 16% of energy. The linoleic acid group was instructed to increase PUFA intake to 15% of energy and to reduce saturated fatty acid intake to less than 10% of energy; participants were provided with liquid safflower oil and a safflower oil based margarine to be used instead of animal fats for cooking, baking, and spreading. Safflower oil is 75% linoleic acid and does not provide other PUFAs. Follow-up was a median of 39 months. Total cholesterol was lowered by an average of 13% in the linoleic acid group."

But despite the reduction in cholesterol the outcome for cardiovascular mortality worsened significantly with the high omega-6 fatty acid diet:

"The intervention group (n=221) had higher rates of death than controls (n=237) (all cause 17.6% v 11.8%, hazard ratio 1.62; cardiovascular disease 17.2% v 11.0%, 1.70; coronary heart disease 16.3% v 10.1%, 1.74. Inclusion of these recovered data in an updated meta-analysis of linoleic acid intervention trials showed non-significant trends toward increased risks of death from coronary heart disease (hazard ratio 1.33 and cardiovascular disease 1.27."

The editorialist for BMJ brings these findings in to focus:

"The authors then used the new data generated from the Sydney Diet Heart Study to update an earlier meta-analysis. Two other linoleic acid intervention trials that reported CHD and CVD mortality were included. This updated analysis reported an increased risk of death from CHD and CVD, although the results were not significant. These findings argue against the “saturated fat bad, omega 6 PUFA good” dogma and suggest that the American Heart Association advisory that includes the statement “higher [than 10% of energy] intakes [of omega-6 PUFAs] appear to be safe and may be even more beneficial” may be misguided. The more cautious UK dietary recommendations on fat and fatty acids, which include the statement, “There is reason to be cautious about high intakes of omega 6 PUFAs,” seem fully justified in the light of the current study’s findings."

The authors of the research study themselves conclude:

"Advice to substitute polyunsaturated fats for saturated fats is a key component of worldwide dietary guidelines for coronary heart disease risk reduction. However, clinical benefits of the most abundant polyunsaturated fatty acid, omega 6 linoleic acid, have not been established. In this cohort, substituting dietary linoleic acid in place of saturated fats increased the rates of death from all causes, coronary heart disease, and cardiovascular disease. An updated meta-analysis of linoleic acid intervention trials showed no evidence of cardiovascular benefit. These findings could have important implications for worldwide dietary advice to substitute omega 6 linoleic acid, or polyunsaturated fats in general, for saturated fats."

Bottom line: the data offer no evidence for clinicians to advise increasing the ratio of omega-6 fatty acids (such as linolenic acid in corn, sunflower, safflower, and soybean oils) to saturated fats for cardiovascular health.