The use of soybean oil has increased dramatically over the last few decades, to the extent that is has become the most widely consumed edible oil in the US and other Western nations. However, its rise has coincided with an alarming escalation in metabolic conditions like diabetes, insulin resistance, and obesity, and a new study indicates that this may be down to the way that soybean oil causes genetic changes in the brain.
Previous research has shown that mice fed a diet that is high in soybean oil are much more likely to develop these conditions than rodents fed on other fats like coconut oil. Further studies hinted that the culprit may be linoleic acid, as mice that consumed soybean oil that had been modified to lack this key ingredient were spared many of these harmful effects.
To better understand how soybean oil produces these negative consequences, scientists decided to investigate its impact on the expression of genes in the hypothalamus, a brain region that regulates metabolism and a range of other essential processes.
Mice were split into groups, of which one received a diet that was high in normal soybean oil, another consumed a diet high in soybean oil that lacked linoleic acid, and another was fed on a diet rich in coconut oil.
Writing in the journal Endocrinology, the study authors explain that soybean oil was found to modify the expression of around 100 different genes in the hypothalamus, affecting processes such as metabolism, neurological disease, and inflammation.
Among the altered genes were some that are associated with schizophrenia, depression, and Alzheimer’s disease, although by far the most affected was a gene that codes for the production of a hormone called oxytocin.
Oxytocin is sometimes referred to as the “love hormone” as it promotes social bonding and feelings of euphoria, and disruptions to its functioning have been linked to depression and autism. However, it also plays a key role in regulating body weight and glucose metabolism, and mice fed on soybean oil were therefore found to suffer from glucose intolerance, while those fed on coconut oil had no such problems.
Furthermore, the oxytocin gene was affected equally in mice that consumed regular soybean oil and the version that lacked linoleic acid, suggesting that the removal of this ingredient does not protect against the harmful effects of soybean oil.
With linoleic acid ruled out as the main driver of these harms, the researchers turned their attention to another compound found in soybean oil called stigmasterol. A further group of mice were fed a diet rich in coconut oil that had been modified to contain high quantities of stigmasterol, to see if this caused similar genetic changes within the hypothalamus.
Yet no such genetic alterations were found in the hypothalamus of these mice, indicating that stigmasterol is not to blame for the dangers of soybean oil.
Future research will now need to focus on determining which ingredient is responsible for these genetic changes, although study author Poonamjot Deol of the University of California, Riverside says that while many questions remain unanswered, some very concrete statements can be made off the back of this study.
"If there's one message I want people to take away, it's this: reduce consumption of soybean oil," she said in a statement.