A new study out of University of California, Riverside (UCR) finds that diets high in Soybean Oil may contribute to obesity—not by calories alone, but through how the body processes its omega-6 fats. On November 30, 2025, researchers reported that feeding mice a soybean-oil–rich diet led most of them to gain significant weight.
The culprit appears to be a group of molecules called “oxylipins,” produced when the body metabolizes linoleic acid, a common omega-6 in soybean oil. These oxylipins seem to trigger inflammation, alter liver behavior, and shift gene activity linked to fat storage.
Importantly, in a group of genetically modified mice—with a different version of a liver-regulating protein—those weight and liver-fat changes did not occur, even on the same soybean-oil diet. That suggests individual biology plays a big role, and the results might vary in humans.
While the study doesn’t claim soybean oil “causes” obesity in people, it raises a warning: heavy use of linoleic-acid–rich oils might silently contribute to metabolic stress.