Researchers from the University of California – Riverside (UCR) in the US noted that soybean oil is used for fast food frying, added to packaged foods, and fed to livestock in many parts of the world.
The study, published in the journal Endocrinology, compared mice which were fed three different diets high in fat: soybean oil, soybean oil modified to be low in linoleic acid, and coconut oil.
In 2015, the same research team found that soybean oil induces obesity, diabetes, insulin resistance, and fatty liver in mice. A 2017 study by the group showed that if soybean oil is engineered to be low in linoleic acid, it induces less obesity and insulin resistance.
However, in the latest study, the researchers, including study first author Poonamjot Deol from UCR, did not find any difference between the modified and unmodified soybean oil’s effects on the brain.
They found pronounced effects of the oil on the hypothalamus, a region of the brain where a number of critical processes take place.
“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,” said Margarita Curras-Collazo, an associate professor at UCR, and lead author of the study.
The team determined a number of genes in mice fed soybean oil were not functioning correctly.
One such gene produces the “love” hormone, oxytocin. In soybean oil-fed mice, levels of oxytocin in the hypothalamus went down.
The researchers discovered roughly 100 other genes also affected by the soybean oil diet. They believe this discovery could have ramifications not just for energy metabolism, but also for proper brain function and diseases such as autism or Parkinson’s, the researchers said.
However, it is important to note there is no proof that the oil causes these diseases, they said. The team noted the findings only apply to soybean oil — not to other soy products, or to other vegetable oils.
“Do not throw out your tofu, soymilk, edamame, or soy sauce,” said Frances Sladek, a UCR toxicologist, and professor of cell biology.
“Many soy products only contain small amounts of the oil, and large amounts of healthful compounds such as essential fatty acids and proteins,” Sladek said.
Since the research was conducted in mice, the researchers caution that the study might not translate to the same results in humans.
As oxytocin is so important for maternal health and promotes mother-child bonding, the researchers said similar studies need to be performed using female mice.
The researchers have not yet isolated which chemicals in the oil are responsible for the changes they found in the hypothalamus.
However, they have ruled out two candidates: linoleic acid, since the modified oil also produced genetic disruptions, and stigmasterol — a cholesterol-like chemical found naturally in soybean oil.