A new study comparing vegetable oils suggests an essential fatty acid has a stronger tie to weight gain than saturated fat intake.
Soybean oil genetically modified to have low linoleic acid (LA) induced less obesity and insulin resistance in mice than conventional soybean oil, according to the study in Nature Scientific Reports. However, the oils demonstrated similar effects on diabetes and the development of fatty liver.
Interestingly, mice on a coconut-oil based diet—the highest in saturated fat—gained the least weight. The conventional soybean oil dieters gained the most, with differences becoming apparent about eight weeks into the 24-week trial.
Coconut oil naturally has low LA, while regular soybean oil is relatively high in LA.
LA is necessary for humans and animals to function. However, only 1 to 2 percent is required, the researchers said, and Americans average 8 to 10 percent in their diets.
“A dietary overload of even essential fatty acids can have significant implications for health,” wrote the researchers, led by Frances Sladek, a professor of cell biology at University of California, Riverside.
The authors put at least 12 mice on each of three high-fat diets aligned with current American fat intake levels and one control diet of normal lab food. The difference in the high-fat diets was what type of oil was used—coconut oil, conventional soybean oil or Plenish, the genetically modified brand.
“We found all three oils raised the cholesterol levels in the liver and blood, dispelling the popular myth that soybean oil reduces cholesterol levels,” Sladek said in a press release.
Plenish is commonly used in restaurants, as is conventional soybean oil. Plenish is engineered to be similar in composition to olive oil because olive oil is generally considered to be healthful.
The researchers pointed out soybean oil is the component of the American diet that has increased the most in the last century. They have widely replaced lard and fat-based products in cooking, likely because of the assumption unsaturated fats are healthy.
In addition to their primary experiment, the researchers tested olive oil. Its effects were nearly identical to that of Plenish, including the presence of enlarged livers and liver dysfunction.
“I used to use exclusively olive oil in my home, but now I substitute some of it for coconut oil,” Sladek said. “Of all the oils we 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. …
“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.”