A recent analysis of a decades-old study on the benefits of vegetable oils revealed no health benefits of polyunsaturated fats.

According to a recent review paper of a five-decade-old trial seeking to test the cholesterol-lowering effects of vegetable oils, replacing saturated-fat-rich butter with healthier polyunsaturated fats in vegetable oils does not lower the levels of bad cholesterol (LDL) in the long run.

The recovered trial, dubbed the Minnesota Coronary Experiment (MCE), is one of the most detailed and rigorously conducted trial on the health benefits of linoleic acid, a healthy fatty acid found in vegetable oils.

For more than a century, the study was used as a cornerstone of the idea that vegetable oil is healthier than butter. People have been thought that the healthier fats in vegetable oils can keep bad cholesterol in check and prevent heart disease.

But the authors of the latest research found that subsequent trials had never established a cause-and-effect link between linoleic acid and better health outcomes. Study authors also had access to research materials that had never been made public such as lead author’s master thesis on MCE, abstracts, unedited data, and grants.

The new evidence revealed that the 9,423 trial participants were living in nursing homes or psychiatric facilities. The experiment focused on these people because they were less likely to skip a meal. So, the settings were ideal places to test the theory that linoleic acid may lower risk of heart disease, stroke, and coronary death.

According to the new documents, hospitals swapped animal fat with corn oil and margarine in salads and other foods including ground beef and different types of cheese. The change lowered the amount of saturated fat by 50 percent and boosted the consumption of linoleic acid by 280 percent. There was also a control group that consumed only high-fat foods.

MCE results initially showed that consuming more vegetable oils reduced cholesterol, but surprisingly that didn’t decrease mortality risk. In reality, study participants who experienced lower cholesterol levels at the end of the trial had a higher risk of death.

In fact, a separate experiment called the Sydney Heart Trial showed that a higher intake of linoleic acid was associated with a higher risk of developing heart disease.

The MCE trial also showed that risk of death was higher in older participants, i.e. those 65 years old and up. This particular group was 35 percent more likely to die prematurely after the food change than their younger peers.

The review paper was published this week in the journal BMJ.

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