Soybean oil is used for frying, for making foods like margarine and salad dressing, and for many industrial applications. It's the most commonly produced and consumed edible oil in the United States and is among the most popular in the world. It has been promoted as a 'good' fat because it contains polyunsaturated fats, which are linked to heart benefits. In a mouse model, however, the fat has been shown to induce metabolic diseases like diabetes and obesity. New research reported in the journal Endocrinology has suggested that the oil can also impact neurological function and may influence the development of anxiety, depression, autism, and Alzheimer's disease.
In this work the researchers fed mice diets rich in one of three types of fat: soybean oil, coconut oil, or soybean oil that was genetically engineered to have low levels of linoleic acid. The soybean oil significantly impacted the hypothalamus, whole the coconut oil had no such effects.
"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 lead study author Margarita Curras-Collazo, a UCR associate professor of neuroscience.
There were about 100 genes that were not being properly expressed when mice were fed soybean oil, the researchers found. Some of those altered genes function in the hypothalamus, including oxytocin, also known as the love hormone.
The study authors noted that these findings were specific to soybean oil and not other oils, and are not applicable to soy-based foods. This research was also conducted using a mouse model, and while they share many similarities with humans, they are also obviously different, and more work will be needed to confirm these conclusions in people.
"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 researchers (seen in the video above discussing previous, related work) are trying to learn more about which compound in soybean oil is responsible for the changes in the hypothalamus. They know it's not linoleic acid or a chemical that is similar to cholesterol called stigmasterol. They plan on identifying it in future work.
"This could help design healthier dietary oils in the future," said the first study author Poonamjot Deol, an assistant project scientist in Sladek's laboratory.
"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," Sladek said.
"If there's one message I want people to take away, it's this: reduce consumption of soybean oil," Deol added.