First, a refresher course on fats:
- Saturated fats, found in high-fat dairy, meats, and fried foods, as well as trans-fats, found in processed foods such as chips and cookies, should be limited. Experts agree they raise the risk of heart disease.
- Unsaturated fats, in moderation, are considered heart-healthy, overall. These include monounsaturated fats and polyunsaturated. Monounsaturated fats are found in olive oil, nuts, and other foods. Polyunsaturated fats can be broken down into two types: omega-6 fatty acids, found in soybean oil, corn oil, and safflower oil; and omega-3 fatty acids, also in soybean and canola oil and in nuts and some fish as well.
What's the ''back story'' on omega-6 fatty acids?
While polyunsaturated fatty acids -- which include omega-3 and omega-6 fatty acids -- are viewed as heart-healthier fats, the information about the benefits of omega-6 fatty acids is more limited, says Christopher Ramsden, MD, a clinical investigator at the National Institutes of Health. He led the research.
Because many oils often contain both, it has been difficult to know which is healthier than the other.
The benefits of foods with both omega-3 and omega-6 fatty acids (such as many vegetable oils) may be due more to the omega-3 fatty acids, says Ramsden. "We suspect that omega-6 might not be as healthy as omega-3," he says.
Different fatty acids may have different effects on heart health, he says.
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."
What should we do now when it comes to watching how much fat we eat?
"Stay the course," Lichtenstein says. That means ''a moderate fat intake with relatively low saturated and trans fat, and the balance of unsaturated including polyunsaturated and monounsaturated [such as olive oil]."
''People don't eat in percents," she says. "Limit animal fat, such as meat and dairy fat, and partially hydrogenated oils [or trans fats, found in baked goods and fried foods]. Use liquid vegetable oil."
For those who count their fat grams: If you eat 2,000 calories a day, total fat intake should be 56 to 77 grams, according to the American Heart Association. Most of that should come from unsaturated fats.
Ramsden and others suggest picking products with lower amounts of omega-6. To do so, choose canola or olive oil, Ramsden says, instead of safflower or sunflower.
"The concerning foods would be oil sources of safflower, corn, and sunflower, because they have almost no omega-3 and higher levels of omega-6," says Richard Bazinet, PhD, associate professor of nutritional sciences at the University of Toronto.
He reports research support from the International Life Sciences Institute of North America and Bunge Ltd., a food company, for studies on omega-3 and omega-6 fatty acids and the brain.
Another expert says to focus on the big picture. "Rather than focusing on individual fats, focus on dietary patterns that we know are associated with better heart health," suggests Sheila Innis, PhD, professor of pediatrics at the University of British Columbia.
For instance, she says, follow a Mediterranean diet pattern, known to lower heart disease risk. The diet includes olive oil as well as plenty of fruits, vegetables and whole grains. It limits meats and sweets.
Innis serves on the Unilever scientific advisory board.
SOURCES: Christopher Ramsden, MD, clinical investigator, National Institutes of Health, Bethesda.Ramsden, C. BMJ, Feb. 5, 2013 published online.Calder, P. BMJ, Feb. 5, 2013 published online.Harris, W. Circulation, Jan. 26, 2009 published online.Alice Lichtenstein, D.Sc., professor of medicine, Tufts University, Boston; spokesperson, American Heart Association.Richard Bazinet, PhD, associate professor of nutritional sciences, University of Toronto, Canada.Sheila Innis, PhD, professor of pediatric, University of British Columbia, Canada.
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