Just when we thought we had it all figured out — saturated fat is bad; polyunsaturated fats or PUFAs are good — it turns out our bodies may have a different idea. Using new evidence from an old study, researchers in the U.S. and Australia have called into question the diet advice to avoid animal fats rich in saturated fatty acids in favor of the polyunsaturated fatty acids or PUFAs found in vegetable oils to help reduce the risk of heart disease.

The researchers used recovered data from The Sydney Diet Heart Study conducted from 1966 to 1973. It involved 458 men aged 30 to 59, all of whom had had a recent coronary event. The new meta-analysis considers overlooked data and uses modern statistical methods.

Findings Surprise Researchers
Half of the Sydney Diet study participants had been told to reduce their saturated fat consumption to less than 10 percent of total energy intake and to increase their omega-6 linoleic acid (by using safflower oil and safflower oil-containing margarine) consumption to 15 percent of their overall energy intake. The other participants, the control group, received no specific dietary advice.

The men who substituted omega-6 fatty acids in place of saturated fats had higher rates of death from all causes, coronary heart disease and cardiovascular disease, a surprising finding that runs counter to the current wisdom that saturated animal fats are linked to many heart problems.

The findings argue against the dogma that saturated fat is bad, and omega-6 PUFA is good, and suggest that the American Heart Association guidelines on omega-6 PUFAs may be misguided.

There are two major types of polyunsaturated fatty acids: omega-6 and omega-3s. Because safflower oil is a rich source of linoleic acid, but does not contain omega-3s, the study data provided researchers a window into the effects of a diet rich in omega-6 polyunsaturated fats, but not omega-3s.

According to Christopher Ramsden, a clinical investigator with the U.S. Public Health Service, only those trials that increased participants’ consumption of omega-3 fatty acids offered some cardiovascular benefit. The supposedly heart-healthy omega-6 fatty acids conferred no protection from heart disease.

Ramsden told TheDoctor, “I think that this fills an important gap in the evidence, and can be looked at in the context of the other evidence out there to determine what dietary advice to give.” Ramsden said they wanted to recover the data so that the policymakers who make decisions and issue guidelines would have all of the evidence at their disposal.

Safflower, sunflower, corn, and soybean oil are all rich in omega-6 PUFAs. Soybean oil contains both omega-3s and omega-6 polyunsaturates. In addition, study participants consumed about twice as much linoleic acid compared to the average American.

Different molecules make up omega-6 and omega-3 fatty acids. Each offers a variety of nutrients, and each of these individual molecules has a different biochemical, and maybe even clinical, effect according to Ramsden. Although the original focus of the study was on the effect of PUFA consumption on blood cholesterol levels, it appears that these compounds act on biochemical processes such as oxidation and inflammation.

These processes are important in cardiovascular disease and possibly other illnesses, making the relationship between diet and heart disease appear to be the result of a much more interconnected set of biochemical events than was originally thought.

An editorial accompanying the article in the British Medical Journal, Philip Calder, a professor at the University of Southampton points out that the findings argue against the dogma that saturated fat is bad, and omega-6 PUFA is good, and suggest that the American Heart Association guidelines on omega-6 PUFAs may be misguided. They also "underscore the need to properly align dietary advice and recommendations with the scientific evidence base."

It would be a mistake to take the results as an endorsement of a diet high in saturated fats or to throw out your safflower oil. But they do seem to suggest that PUFAs operate in concert with one another and that it is important to get enough omega-3s. Because all the participants in the Sydney Diet Heart Study had had a recent coronary event, the findings may or may not be applicable to those of us who have not had heart problems.