If you’ve been confused by recent headlines suggesting “Butter Is Back” and studies questioning the link between saturated fat and heart disease, a new meta-analysis may set the record straight. The research found that people who swap 5% of the calories they consume from saturated fat sources such as red meat and butter with foods containing linoleic acid—the main polyunsaturated fat found in vegetable oil, nuts and seeds—was associated with a 9% lower risk of coronary heart disease events. Switching from saturated fat to linoleic acid was also associated with a 13% lower coronary heart disease mortality risk.
“This is a very important study,” says Alice H. Lichtenstein, DSc, director of Tufts’ HNRCA Cardiovascular Nutrition Laboratory. “Prior work has not consistency taken the replacement dietary component, fat or carbohydrate, into consideration when drawing conclusions about the effects of saturated fat in the diet and heart-disease outcomes. This study has accomplished this, focusing on the effect of swapping out saturated fat and replacing it with polyunsaturated fat. The results are clear and consistent with current dietary guidance—there is a benefit.”
SWAP FOR SATURATED FAT, CARBS: In the study, published in Circulation, researchers performed a systematic review of 13 published and unpublished studies totaling 310,602 participants. The studies focused on dietary linoleic acid intake and heart disease risk in generally healthy people.
Results showed that dietary linoleic acid intake was inversely associated with heart-disease risk in a dose-response manner—that is, higher intake of linoleic acid resulted in a lower risk of heart disease. Compared to those with the lowest intake, those who consumed the most dietary linoleic acid had a 15% lower risk of heart-disease events and a 21% lower risk of coronary deaths. The results were independent of common risk factors such as smoking and other dietary factors.
The researchers also found another benefit associated with linoleic acid: Substitution of 5% of calories from carbohydrates with linoleic acid was associated with similar reductions in risk of heart disease.
FAT SMARTS: Lead author Maryam S. Farvid, PhD, a visiting scientist at the Harvard School of Public Health, says the results support replacing butter, lard and fat from red meat with liquid vegetable oils in commercially prepared foods, cooking and at the table. Says Farvid, “Randomized clinical trials have shown that replacing saturated fat with linoleic acid reduces total and LDL cholesterol.”
Linoleic acid is the primary omega-6 polyunsaturated fatty acid in the Western diet, found in liquid vegetable oils such as soybean, sunflower, safflower and corn (See “Take Charge!” Above) as well as nuts and seeds. A tablespoon of soybean or corn oil contains about seven to eight grams of linoleic acid, and seven shelled walnuts provide about 11 grams. All fats contain about nine calories per gram, so 1.5-3 tablespoons of vegetable oil daily would provide 5%-10% of calories from linoleic acid (100-200 calories based on a 2,000-calorie daily diet), enough to meet current guidelines.
Says Lichtenstein, “The emphasis should be on replacing animal fat with these sources of linoleic acid, not adding sources of linoleic acid rich foods/oils to the diet.”
What about concerns that linoleic acid might actually be harmful for heart health by increasing inflammation? Farvid says this speculation is not supported by randomized controlled feeding studies, in which dietary intake of linoleic acid was not found to increase blood levels of arachidonic acid (associated with inflammation) or inflammatory markers. “On the contrary, some studies have found anti-inflammatory effects of diets higher in linoleic acid compared to those higher in saturated fat.”