Americans have been told to swap out all saturated fat with unsaturated fat to reduce the risk of heart disease. Cooking with vegetable oil to reduce saturated fats may lower cholesterol, but it may not cut the risk of heart disease or even prolong life, a new study suggests.

Researchers conducted the Minnesota Coronary Experiment (MCE), which aims to examine traditional diet-heart hypothesis through recovery and analysis of unpublished data in the past. With the experiment on more than 9,400 people who were randomly assigned to specific diets to see how foods and fats affected health and lifespan, they found that lower cholesterol did not actually lead to improved survival.

The MCE study was originally conducted from 1968 to 1973 at seven different long-term care facilities. The researchers from the National Institutes of Health and the University of North Carolina gathered data from more than 2,300 participants.

They were divided into two groups — one group swapped saturated fat for unsaturated vegetable oil from corn oil margarine or corn oil, while the other group continued with their saturated fat consumption.

Over the span of the study period, those who swapped to vegetable oil did have lower cholesterol levels compared with the other group. The researchers, however, found no change in the rate of heart problems and even death.

The patients who swapped to vegetable oils had a nearly 14 percent reduction in cholesterol levels compared with just one percent among those who did not swap saturated oils.

The researchers have found that, for every 30 mg/dL of decrease in serum cholesterol, the risk of death increased by 22 percent. They also found that swapping to vegetable oil does not reduce the risk of atherosclerosis, a disease wherein plaque deposits form in the wall of the vessel, making it hard for blood to pass through properly.

"Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid," the researchers concluded.

The American Heart Association (AHA) recommends that all Americans over the age of two eat between 25 and 35 percent of total daily calories from fats like vegetable oils, fish and nuts. It also recommends limiting the intake of saturated fats. 

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