The oil extracted from soybeans is used to produce everything from salad dressings, to frying fats, to margarines, to cooking oil and more. According to the Department of Agriculture, it is the most consumed oil in the United States.
In 2015, UC Riverside researchers discovered that soybean oil induces obesity, diabetes, insulin resistance, and fatty liver in mice. Fast forward to 2020, and that same team found that soybean oil could also affect neurological conditions such as autism, Alzheimer's disease, anxiety, and depression.
“Dysregulation of Hypothalamic Gene Expression and the Oxytocinergic System by Soybean Oil Diets in Male Mice,” examined mice on different diets high in fat. The three diet groups were soybean oil, coconut oil, as well as modified soybean oil low in linoleic acid.
The study, published in the journal Endocrinology, did not find any difference between the modified and unmodified soybean oil's effects on the brain. This is in contrast to one of their earlier studies, which did find that if soybean oil is modified to be low in linoleic acid, it would cause less obesity and insulin resistance.
The research team did find noticable effects of the oil on the hypothalamus, a small part of the brain that plays a crucial role in many important functions, such as releasing hormones.
"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.
Researchers did not detect which chemicals in the soybean oil are behind the changes they found in the hypothalamus. However, they did rule out linoleic acid, since the modified oil also produced genetic disruptions. They also excluded stigmasterol, a cholesterol-like chemical found naturally in soybean oil.
Love on the brain
The team found that the mice on the soybean oil diet had a number of genes that were not functioning properly. One such gene produces oxytocin, also known as the "cuddle hormone" or the "love hormone," because oxytocin is released when people snuggle or bond. In soybean oil-fed mice, the researchers noted that oxytocin levels in the hypothalamus went down.
The authors said that about 100 genes were also found to be impacted by the soybean oil diet. “The results show that compared to the coconut oil and low-fat control diets, the two soybean oil-based diets resulted in a significant dysregulation of more than 100 hypothalamic genes including those involved in neurochemical and neuroendocrine pathways and metabolic and neurological disorders.”
The authors added the findings could mean consequences related to energy metabolism, proper brain function and neurological conditions like autism or Parkinson's disease.
“The results presented here demonstrating the impact of dietary soybean oil on gene expression in the hypothalamus lead to the provocative suggestion that dietary fat, in general, and soybean oil, in particular, may have an impact on mental as well as metabolic health. The results also clearly indicate that additional studies are needed to determine the effects of both high linoleic acid and low linoleic acid soybean oil on hypothalamic, and potentially other brain function and underscore the need for a careful evaluation of the extensive use of soybean oil-based food products, including infant formula, animal feed and other processed foods.”
Don’t toss your soy milk
The researchers noted the findings only apply to soybean oil—not to other soy products or to other vegetable oils.
It is also worth noting that there is no proof the oil causes the diseases mentioned in the study.
More studies are needed, as animal studies do not always translate to the same results in humans. Additionally, this study only used male mice. Given oxytocin is vital in maternal health, similar studies need to be performed using female mice.
The authors said they hope this study will help in the design of healthier dietary oils. They added that their future research will be focused on identifying the compounds behind the negative effects.
"Dysregulation of Hypothalamic Gene Expression and the Oxytocinergic System by Soybean Oil Diets in Male Mice"
08 January 2020 https://doi.org/10.1210/endocr/bqz044
Authors: P. Deol, et al