Soybean oil is used in countless everyday foods, from salad dressings to packaged snacks, and it’s the most widely consumed cooking oil in the U.S. A new mouse study from UC Riverside offers early insights into how the body processes one of its major components and why some animals may respond differently to diets high in this oil.
In the experiment, most mice eating a high-fat diet rich in soybean oil gained weight. But a genetically engineered group did not. These mice carried a slightly different form of a liver protein called HNF4α that helped regulate hundreds of genes tied to fat metabolism. According to the research team, this protein variant also appeared to influence how the body handled linoleic acid, a common fatty acid naturally present in many plant-based oils, including soybean oil.
“This may be the first step toward understanding why some people gain weight more easily than others on a diet high in soybean oil,” said study author Sonia Deol.
The study builds on earlier UCR work examining how oils with different fatty acid profiles affect metabolism in rodents.
“We’ve known since our 2015 study that soybean oil is more obesogenic than coconut oil,” said Frances Sladek. “But now we have the clearest evidence yet that it’s not the oil itself, or even linoleic acid. It’s what the fat turns into inside the body.”
As the mice processed linoleic acid, their bodies produced compounds called oxylipins. The altered mice generated fewer of these oxylipins and showed healthier liver profiles despite eating the same diet. They also displayed stronger mitochondrial function, which may have contributed to their resistance to weight gain.
Researchers caution that these findings are specific to mice and controlled lab diets. Other factors, such as genetics, medications, age, stress or the total amount of fat consumed, could all influence metabolic responses. The team also emphasizes that the research should not be interpreted as a warning against soybean oil itself.
“Soybean oil isn’t inherently evil,” Sladek said. “But the quantities in which we consume it is triggering pathways our bodies didn’t evolve to handle.”
She added that oxylipin formation is tied to overall intake levels, particularly from ultraprocessed foods high in added fats.
No human studies were conducted, and researchers noted that other oils high in linoleic acid, including corn and sunflower oil, may show similar metabolic patterns, a question for future research.
“We hope it won’t take that long for society to recognize the link between excessive soybean oil consumption and negative health effects,” Sladek said.
The study, which was published in the Journal of Lipid Research, was supported by the U.S. National Institute of Environmental Health Sciences, the National Institute of Diabetes and Digestive and Kidney Diseases, and a pilot project award from the National Institutes of Health.