Switching to Polyunsaturated Fat Cuts Heart Disease Risk

The report clinically provides the “first conclusive evidence” that the proportion of different fats in one’s diet has a clear impact on heart health. It was done by researchers at the Harvard School of Public Health (HSPH). Cutting dietary calories in saturated fat and replacing them with calories from polyunsaturated fat, the study shows, can lower the risk of having a heart attack or dying of heart disease by 19 percent. 

Intake of saturated fat is generally associated with eating food items like butter, pastries, cookies, lard, cheese and fatty meat. Polyunsaturated fat is commonly found in most vegetable oils.

The most important takeaway from the study is that simply reducing dietary saturated fat is not as valuable as what it’s replaced with. If a person replaces saturated fat intake with refined sugars and starches, then there might be little or no gain in terms of heart health. But, according to the report, if the replacement calories are in the form of polyunsaturated fat, a gain can result. 

“The specific replacement nutrient for saturated fat may be very important,” said lead author Dr. Dariush Mozaffarian. He is an assistant professor in HSPH’s department of epidemiology and in the department of medicine at Harvard Medical School. “Our findings suggest that polyunsaturated fats would be a preferred replacement for saturated fats for better heart health.”

The study by Mozaffarian and his co-workers took the form of a meta-analysis of eight randomized clinical trials. In a meta-analysis, scientists take data from several studies, and pool them in such a way that they can compare “apples to apples.” The researchers in the HSPH investigation carefully selected the eight studies to ensure that coronary heart disease episodes were recorded among participants. They also wanted studies that had chosen an “appropriate” control group and that had randomized patients to increased polyunsaturated fat consumption for at least a year. But the most important criterion was that subjects specifically substituted polyunsaturated fat for saturated fat in their diet. In fact, about 15 percent of their daily calories came from polyunsaturated fat, much of which had displaced saturated fat. 

The eight trials included 13,614 participants who experienced 1,042 coronary heart disease episodes. Analyzing the pooled data, the scientists found that: 

-- When polyunsaturated fat was substituted for saturated fat in the diet, the risk of heart attack or heart failure was cut by 19 percent (compared to controls who failed to change their diet). 

-- The risk of heart attack or heart failure fell by 10 percent for every 5 percent rise (measured as total energy) in polyunsaturated fat intake. 

-- The benefits connected with consumption of polyunsaturated fat swelled as the trials increased in length. 

The study was sponsored by the National Heart, Lung and Blood Institute and a Searle Scholar Award from the Searle Funds at the Chicago Community Trust. 

 Sources: Harvard School of Public Health, PLoS Editors' Summary