Used for fast food frying, added to packaged foods, and fed to livestock, soybean oil is the most widely produced and consumed edible oil in the US, according to the US Department of Agriculture (USDA).
New University of California, Riverside (UCR) research has shown that soybean oil not only leads to obesity and diabetes, but could also affect neurological conditions like autism, Alzheimer’s disease, anxiety and depression.
The UCR research team found in 2015 that soybean oil induces obesity, diabetes, insulin resistance, and fatty liver in mice. Then in a 2017 study, the same group learned that if soybean oil is engineered to be low in linoleic acid, it induces less obesity and insulin resistance.
However, in this new study, the researchers did not find any difference between the modified and unmodified soybean oil’s effects on the brain. Specifically, the scientists found pronounced effects of the oil on the hypothalamus, where a number of critical processes take place.
The study compared mice fed three different diets high in fat: soybean oil, soybean oil modified to be low in linoleic acid, and coconut oil.
“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, a UCR associate professor of neuroscience and lead author on 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 research team discovered approximately 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 disease. However, the researchers noted that there is no proof the oil causes these diseases.
“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.”
The study utilised male mice, and because oxytocin is important for maternal health and promotes mother-child bonding, similar studies need to be performed using female mice, the researchers explained.
The team also noted that they have not yet isolated which chemicals in the oil are responsible for the changes they found in the hypothalamus. However, they have stated that it is not linoleic acid, since the modified oil also produced genetic disruptions; nor is it stigmasterol, a cholesterol-like chemical found naturally in soybean oil.
Identifying the compounds responsible for the negative effects is said to be the focus for the team’s future research.
“This could help design healthier dietary oils in the future,” said Poonamjot Deol, an assistant project scientist in Sladek’s laboratory and first author on the study.
“The dogma is that saturated fat is bad and unsaturated fat is good. Soybean oil is a polyunsaturated fat, but the idea that it is good for you is just not proven,” Sladek said.
Coconut oil, which contains saturated fats, produced very few changes in the hypothalamic genes.
“If there is one message I want people to take away, it is this: reduce consumption of soybean oil,” Deol concluded.