The health risks posed by using soybean oil, the most popular edible oil in the United States for decades, are still a matter of debate among health professionals.

Soybean oil is a widely-used industrial ingredient among food firms that make processed and premade foods. It's also popular with restaurants because it's relatively cheap. Soybean oil is by far the most widely produced and consumed edible oil in the America, as per the U.S. Department of Agriculture (USDA).

A study back in 2015 found soybean oil might cause obesity, insulin resistance and diabetes in mice, for example. Others said Americans should consider avoiding plant oils such as soybean oil, canola oil, corn oil and cottonseed oil due to their high omega-6 content. Omega-6 fatty acids are a type of polyunsaturated fat found in vegetable oils, nuts and seeds that may or may not pose dangers to one's health.

A new study from the University of California, Riverside (UCR) found soybean oil impacts the brain’s hypothalamus in mice fed diets high in this oil. It revealed consumption of soybean oil seems to have impaired the ability of around 100 genes to function properly in the mice. One of these genes is responsible for producing oxytocin, a hormone also called the body’s "love drug." The study said these changes were only associated with soybean oil, but not with other soy products like soy milk or other cooking oils.

The study published this month in the journal, Endocrinology, compared mice fed three different diets high in fat: soybean oil, soybean oil modified to be low in linoleic acid and coconut oil.

In 2015, this same UCR research team found soybean oil induces obesity, diabetes, insulin resistance and fatty liver in mice. The same group in a 2017 study found soybean oil induces less obesity and insulin resistance if engineered to be low in linoleic acid.

Their latest study, however, didn't find any difference between the modified and unmodified soybean oil's effects on the brain. Specifically, they found pronounced effects of the oil on the hypothalamus.

"The hypothalamus regulates body weight via your metabolism, maintains body temperature, is critical for reproduction and physical growth as well as your response to stress," Margarita Curras-Collazo, lead author on the study and a UCR associate professor of neuroscience, said.

The team concluded a number of genes in mice fed soybean oil were not functioning correctly. One such gene produces oxytocin. In soybean oil-fed mice, levels of oxytocin in the hypothalamus decreased.

They believe this discovery could have consequences for energy metabolism and proper brain function and diseases such as autism or Parkinson's disease. The team warned there is no proof soybean oil causes these diseases.

"Do not throw out your tofu, soymilk, edamame, or soy sauce," Frances Sladek, a UCR toxicologist and professor of cell biology, said. "Many soy products only contain small amounts of the oil, and large amounts of healthful compounds such as essential fatty acids and proteins."

The team said their study was conducted on mice, and mouse studies do not always have the same results in humans.

Soybean Oil
Soybean oil contains omega-3 fatty acids, which support heart health, fetal development, brain function and immunity. United Soybean Board/flickr