The number one, most popular choice of cooking oil used today in the United States is soybean oil. It’s used in fast food frying, livestock feeds, and added to many packaged foods. The problem is that it’s very unhealthy. Not only does it lead to obesity and diabetes, new research has also revealed it may also affect certain neurological conditions too including depression, anxiety, autism, and Alzheimer’s disease.

Recent studies carried out at UC Riverside have revealed that soybean oil isn’t for consumption for either human or mouse. During the research mice were given three different high-fat diets. One consisted of just soybean oil. Another was made up of soybean oil that had been modified to be low in linoleic acid. While the third was coconut oil.

In 2015, the same team concluded that some of soybean oil’s detrimental health implications included the inducing of diabetes, obesity, fatty liver, and insulin resistance in mice. Then, just two year later, the same team discovered that soybean oil is much less harmful if engineered to be low in linoleic acid. But in this most recent study, there was no difference in the effect on the brain for either variant of the oil. Instead, what they did find was that a pronounced effect was taking place in the hypothalamus where many of the body’s most critical processes are carried out. 

“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,” explained Margarita Curras-Collazo, an associate professor of neuroscience at UCR and lead author on the study. Part of the research involved determining what genes in the soybean oil fed mice weren’t working properly. The team discovered that one of these genes was responsible for producing oxytocin, otherwise known as the “love hormone”. However, in those mice given soybean oil the level of oxytocin found in the hypothalamus decreased.

Another discovery made as part of the research was that soybean oil in the diet also affected around 100 other different genes. However, the team does make it clear that this just applies to soybean oil and not to vegetable oil or other soy products. And, it should also be noted that this research was carried out on male mice and therefore the results may be different in humans. 

One thing that is yet to be determined is which chemicals in the oil are responsible for the changes they observed in the hypothalamus. All the researchers do know for sure is that it’s not linoleic acid or stigmasterol. But being able to identify the responsible compounds it a vital part of the research. As Poonamjot Deol, an assistant project scientist at UCR and first author on the study said, “this could help design healthier dietary oils in the future.” Adding to that Frances Sladek, a UCR toxicologist and professor cell biology said, “the dogma is that saturated fat is bad and unsaturated fat is good. Soybean oil is a polyunsaturated fat, but the idea that it’s good for you is just not proven.”