Confused About Good Fats? No Wonder

Do you have your doubts about simplistic advice to eat more good fats? That’s probably wise. A new British Medical Journal (BMJ) study found that replacing saturated animal fats with omega-6 polyunsaturated vegetable fats may lead to an increased risk of death in people with heart disease. In this re-analysis of a previous clinical trial of 458 men who had experienced a heart attack or other coronary event and who replaced saturated fats with omega-6 fats, researchers found a 16% rate of death from heart disease, compared with 10% rate for those who did not get dietary intervention.

But experts agree that this study doesn’t negate longstanding dietary advice for heart patients, to replace saturated fats with polyunsaturated fats. It simply adds to our understanding the need for a balance between different kinds of unsaturated fat.

This BMJ paper is actually a new analysis of an old study, the Sydney Diet Heart Study, which was a clinical trial conducted from 1966 to 1973 involving 458 men age 30-59 years who had a recent coronary event — myocardial infarction, acute coronary insufficiency, or angina.

In the original Sydney Diet Heart Study, the participants were randomized to a diet rich in linoleic acid or continued their habitual diet. Both groups were treated the same in other respects and received the same advice. The linoleic acid group was instructed to increase polyunsaturated fatty acids (PUFAs) intake and to reduce saturated fatty acid intake. The participants in the treatment arm of the study were provided with liquid safflower oil and a safflower oil based margarine for cooking and use.

To understand what’s going on here, you need to know about two very different kinds of polyunsaturated fats. Omega-3 fats are found in fish and flaxseed. Omega-6 fats are found in safflower and other vegetable oils. Linioleic acid is the key omega-6 fat. The original analysis in 1978 did not examine the consumption of omega-6 and omega-3 fats separately.

In the new analysis, researchers obtained data to distinguish the effects of omega-6 fats, because newer research has questioned the health effects of omega-6 fats. This new analysis found increase risk of death for cardiovascular events associated with substituting saturated fats with omega-6 fats.

“I don’t think this new analysis study should be practice-changing and lead people to consume fewer polyunsaturated fats,” said Penny Kris-Etherton a Penn State nutrition who worked on American Heart Association recommendations for dietary fat.

Adding more perspective, Walter Willett of the Harvard School of Public Health pointed that nutrition knowledge has grown since this study was first conducted. Newer research has added greater understanding to the differences between omega-3 and omega-6 fats. “Very high intakes of omega-6 polyunsaturated fat intakes without any omega-3 polyunsaturated fat is not desirable,” said Willett. “We do need adequate amounts of both.”

Echoing a theme of caution, David Spiegelhalter, Professor of the Public Understanding of Risk at the University of Cambridge, said, “I would not want to get very excited about this study on its own.”

Click here to read more at and here to read the study in the BMJ.

Safflower image © Paulatz / Wikimedia