Soybean oil, an increasingly common cooking oil, especially in the United States, can cause changes in the brain that could be linked to diabetes, inflammation, and brain disorders, an early study in mice suggests.
This oil, a type of polyunsaturated fat, is used to fry fast foods, added to packaged meals and snacks, and fed to farm animals. Its consumption in the U.S. rose 1,000 times throughout the 20th century, its researchers noted.
The study, “Dysregulation of Hypothalamic Gene Expression and the Oxytocinergic System by Soybean Oil Diets in Male Mice,” was published in Endocrinology.
Most diet-induced obesity studies focus on the role of saturated fats, such as those found in animal fat. But increasing evidence suggests that polyunsaturated fatty acids that are high in linoleic acid — a fatty acid molecule in the omega-6 family — also contribute to obesity.
Previous work by researchers at the University of California, Riverside (UCR), linked soybean oil with obesity, diabetes, insulin resistance, and fatty liver in mice. [Its earlier work also found that polyunsaturated fatty acids high in linoleic acid — a fatty acid molecule in the omega-6 family — contributed to obesity, while soybean oil engineered to be low in linoleic acid did not. This study’s results, however, saw no such distinction.]
To understand if different types of fats caused changes in the brain, the same team fed male mice different high-fat diets: either conventional soybean oil or a soybean oil genetically modified for low amounts of linoleic acid.
Two coconut oil diets were used as a comparison: a regular oil that does not contain linoleic acid or stigmasterol, a cholesterol-like molecule that is another main component of soybean oil, and a coconut oil supplemented with stigmasterol.
The scientists studied the hypothalamus of the mice, a small but complex area of the brain responsible for many important tasks, including homeostasis.
“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,” the study’s lead author, Margarita Curras-Collazo, PhD, an associate professor of neuroscience at UCR, said in a press release.
Researchers found that the soybean oils, but not coconut oils, influenced the activity of the hypothalamus, causing more than 100 genes not to work as expected. Specifically, changes were seen in the gene that produces oxytocin, a hormone that controls key aspects of the reproductive system, such as childbirth and lactation, and aspects of human behavior. Changes in the level of oxytocin in the brain have also been linked with diabetes.
The amount of oxytocin in the hypothalamus dropped, which appeared to cause an increase in glucose sensitivity, an indicator of diabetes. The body weight of the mice did not seem to be affected by the different oils.
“Both the soybean oil-rich diets produced a considerable dysregulation of gene expression in the hypothalamus of male mice, the most notable of which is the gene coding for oxytocin (Oxt),” the researchers wrote. “We also observed elevated levels of circulating OXT peptide in the plasma of soybean oil-fed mice.”
A gene called proprotein convertase subtilisin/kexin type 1 inhibitor (Pcsk1n), which is predictive of Alzheimer’s disease, was found in higher amounts in the hypothalamus of mice fed the soybean oil diets, the study noted.
Changes were also detected in other genes associated with such neurological ills as anxiety, pain, depression or schizophrenia.
Only soybean oil — regardless of its linoleic acid content — appeared to be potentially harmful, the researchers said.
Coconut oil, other vegetable oils (like olive oil), and other soy products (like soy sauce, soy milk, tofu or edamame) do not appear to have the same effect on the brain.
More research is needed, the researchers said, as their work has not yet determined the exact chemicals in soybean oil responsible for changes seen in the hypothalamus. However, this work shows it is not linoleic acid (the modified oil also disrupted genes) or stigmasterol, a cholesterol-like chemical naturally found in soybean oil.
“All told, our results demonstrate that different dietary oils can have differential effects on hypothalamic gene expression,” the study concluded.
It also raises “the possibility that the soybean oil-rich American diet may be not only contributing to increased rates of metabolic disease [obesity, diabetes] but also impacting neurological function.”
Added Poonamjot Deol, an assistant project scientist and the study’s first author, “If there’s one message I want people to take away, it’s this: reduce consumption of soybean oil.”
It is also important to note that the study was done with male mice; results in female mice and, especially, people could differ.
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