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What exactly did the study look at?

Ramsden and his team recovered some unanalyzed data from the Sydney Diet Heart Study, conducted from 1966 to 1973. The study included 458 men, ages 30 to 59, with a history of heart attack or other heart problems.

One group was told to reduce their saturated fat intake to less than 10% of daily calories and increase their polyunsaturated fat intake to about 15% of calories. They were told to use safflower oil or safflower oil margarine, which has linoleic acid, a form of omega-6, but no omega-3 fats.

The other group received no specific instruction on diet.

What did the study find?

When Ramsden compared the two groups three years later,  the group told to boost omega-6 fats fared worse, he says.  "Death from all causes was about 65% higher, and death from coronary heart disease was about 70% higher," he says.

Even when researchers included additional data from earlier studies, they still found a possible increased risk of heart disease with higher omega-6 intakes. The researchers found a link but cannot prove cause and effect.

Why might omega-6 fats be risky for heart health?

One possible explanation, Ramsden says, is that although omega-6 fatty acids lower LDL (the ''bad'' cholesterol) overall, ''it may increase oxidized LDL," he says.

"Oxidized LDL contains free radicals, which are hazardous substances that may contribute to heart disease," he says.

Would the study findings apply only to those who have already had a heart attack, or also to others?

Ramsden can't say, as the study just included those with heart disease.

What does the American Heart Association recommend about omega-6 fat intake?

In a 2009 advisory, the AHA says that taking in 5% to 10% of calories from omega-6 fatty acids lowers the risk of heart disease. Besides vegetable oils, omega-6 fatty acids are also in nuts and seeds.

Will the new study result in the AHA taking another look?

"Certainly the results are important to consider," says Alice Lichtenstein, D.Sc., professor of medicine at Tufts University and a spokeswoman for the American Heart Association. Although the association won’t be drawing any immediate conclusions for Americans, she says it ''does say we probably should be reevaluating the recommendation."

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