Consumption of soybean oil is increasing worldwide and parallels a rise in obesity. Being rich in unsaturated fats, especially linoleic acid, soybean oil is considered healthy, and yet it induces obesity, diabetes, insulin resistance, and fatty liver. Researchers at the University of California, Riverside have tested genetically-modified (GM) soybean oil (Plenish®) which was engineered to generate fewer trans-fats and found that while it induces less obesity and insulin resistance than conventional soybean oil, its effects on diabetes and fatty liver are similar to those of conventional soybean oil. Plenish also induced hepatomegaly and liver dysfunction, as does olive oil. The study was published in Nature Scientific Reports

UC Riverside researchers tested Plenish® which was released by DuPont in 2014. Engineered to have low linoleic acid, Plenish® is similar in composition to olive oil, the basis of the Mediterranean diet and is considered healthful.

The study also compared both conventional soybean oil and Plenish to coconut oil, which is rich in saturated fatty acids and causes the least amount of weight gain among all the high-fat diets tested. It was noted that all three oils raised the liver and blood cholesterol levels, dispelling the popular myth that soybean oil reduces cholesterol levels.

Next, the researchers compared Plenish to olive oil. Both oils have high oleic acid, a fatty acid believed to reduce blood pressure and help with weight loss. Olive oil was found to produce essentially identical effects as Plenish, more obesity than coconut oil, although less than conventional soybean oil and very fatty livers. This was indeed surprising as olive oil is typically considered to be the healthiest of all the vegetable oils. "Plenish, which has a fatty acid composition similar to olive oil, induced hepatomegaly, or enlarged livers, and liver dysfunction, just like olive oil" said Poonamjot Deol, the co-first author of the research paper.

"This could be why our experiments are showing that a high-fat diet enriched in conventional soybean oil has nearly identical effects to a diet based on lard," she said. The researchers further speculate that the increased consumption of soybean oil in the U.S. since the 1970s could be a contributing factor to the obesity epidemic. Obesity, officially designated by the American Medical Association in 2013 as a disease, is linked to diabetes, heart disease, and cancer.

The researchers further speculate that the increased consumption of soybean oil in the U.S. since the 1970s could be a contributing factor to the obesity epidemic which in turn is linked to a set of other diseases like diabetes, heart disease, and cancer.

Frances Sladek, a professor of cell biology, who led the research project, says that their findings do not necessarily relate to other soybean products like soy sauce, tofu, or soy milk products that are largely from the water-soluble compartment of the soybean. Soybean oil, on the other hand, is from the fat-soluble compartment. Researchers also add that more research into the amounts of linoleic acid in these products and others is required. Even though linoleic acid is an essential fatty acid, it does not necessarily mean it is good to have more of it in your diet. While our bodies need just 1-to-2 percent linoleic acid from our diet, Americans, on average, seems to have 8-to-10 percent linoleic acid in their diets.

Researchers recommend avoiding conventional soybean oil as much as possible. One advantage of Plenish is that it generates fewer transfats than conventional soybean oil. Of all the oils these researchers have tested thus far, coconut oil produces the fewest negative metabolic effects even though it consists nearly entirely of saturated fats. Coconut oil does increase cholesterol levels, but no more than conventional soybean oil or Plenish. Since they have not examined the cardiovascular effects of coconut oil, they are not in a position to comment whether the elevated cholesterol that coconut oil induces is detrimental.

The researchers have not examined the cardiovascular effects of coconut oil. "As a result, we do not know if the elevated cholesterol coconut oil induces is detrimental," Sladek said. "The take-home message is that it is best not to depend on just one oil source. Different dietary oils have far reaching and complex effects on metabolism that require additional investigation".The study builds on an earlier study by the researchers that compared soybean oil to a high fructose diet and found soybean oil causes more obesity and diabetes than coconut oil.

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