Scientists at University of California, Riverside found that soybean oil contributes to obesity in a study involving mice.
The oil creates specific fat-derived molecules—oxylipins—that alter liver metabolism and increase fat accumulation, the study, which was published in the Journal of Lipid Research last month, concluded.
Researchers observed that mice fed a high-fat diet rich in soybean oil, the most widely consumed cooking oil in the United States, gained significant weight.
“Soybean oil isn’t inherently evil. But the quantities in which we consume it is triggering pathways our bodies didn’t evolve to handle,” study author Sonia Deol said in a press release issued by UC Riverside.
Why It Matters
The latest research offers new insights into why soybean oil may be obesogenic—at least in animal models—and raises questions about the broader health implications of high linoleic acid intake found in this and similar oils.
Soybean oil is present in countless processed foods and home kitchens. With obesity rates rising nationally, understanding the dietary factors contributing to weight gain is a major concern for Americans, policy makers, and public health experts.
What To Know
Scientists at UC Riverside reported that soybean oil contributes to obesity in mice by creating oxylipins that alter liver metabolism and increase fat accumulation. They also observed that mice fed a high-fat diet rich in soybean oil gained significant weight, while genetically engineered mice with a modified form of the liver protein HNF4α did not, despite consuming the same diet.
This protein influences hundreds of genes related to fat metabolism and changes how the body processes linoleic acid, the primary fatty acid in soybean oil.
The researchers found that excess linoleic acid is converted into oxylipins associated with inflammation and obesity. However, genetically engineered mice produced fewer oxylipins and had healthier liver profiles and better mitochondrial function, which may explain their resistance to weight gain.
Notably, only oxylipin levels in the liver, not the blood, were linked with body weight, indicating that standard blood tests may not reflect early metabolic changes due to diet.
The U.S. has seen a five-fold increase in soybean oil consumption over the past century, moving from about 2 percent to nearly 10 percent of daily calories, according to the study.
Despite containing no cholesterol, the oil’s predominant fatty acid—linoleic acid—has come under scrutiny for its role in metabolic disorders.
The study suggests that the metabolic effects of soybean oil may depend on individual genetic, dietary, and biological factors.
Researchers also reported higher cholesterol levels in mice fed soybean oil, despite its lack of cholesterol—a result that highlights the complexity of dietary fat metabolism.
Registered dietician Nichola Ludlam-Raine previously told Newsweek that saturated fats are “generally considered more harmful and are less preferred, particularly for cardiovascular health,” while seed oils like soybean and sunflower oils contain polyunsaturated fats associated with improved heart health when used moderately.
Recent research has highlighted other health concerns related to cooking oils. Deep frying at high temperatures, particularly with reused oils, increases the production of toxic compounds—including acrylamide, trans fats, and peroxides—that have been linked to metabolic disorders, cancer, and even neurodegeneration in animal studies.
Additionally, cooking sulfur-rich vegetables in vegetable oil at high temperatures can generate small amounts of trans fats, which are associated with increased cardiovascular risk. However, experts say this effect is minimal under normal cooking conditions and is most relevant for those already at high risk for heart disease.
The American Heart Association has consistently recommended that Americans limit trans-fat intake and replace saturated fats with polyunsaturated fats found in vegetable oils, including soybean oil, due to their beneficial effect on cholesterol levels. However, as new evidence emerges on the nuanced metabolic effects of different fatty acids and their derivatives, advocacy groups are closely monitoring research to update dietary guidance as needed.
What People Are Saying
Sonia Deol, UCR biomedical scientist and corresponding study author, said in a press release from UC Riverside: “This may be the first step toward understanding why some people gain weight more easily than others on a diet high in soybean oil.”
Frances Sladek, a UCR professor of cell biology, said in the press release: “It took 100 years from the first observed link between chewing tobacco and cancer to get warning labels on cigarettes. We hope it won’t take that long for society to recognize the link between excessive soybean oil consumption and negative health effects.”
What Happens Next?
The UC Riverside research team said they plan further studies to determine precisely how oxylipin formation leads to weight gain and whether similar mechanisms occur with other oils high in linoleic acid, such as corn, sunflower, and safflower oil.
No human clinical trials are planned yet. Public health groups and nutrition policy makers may consider these findings when updating dietary recommendations.
Researchers also highlighted the need to develop improved screening methods for metabolic risks, as traditional blood tests may fail to capture early diet-linked changes.