Study Reveals Why Some Gain Weight Easier on Soybean Oil Diets

Genetic differences in liver metabolism may explain unequal weight gain on similar diets high in soybean oil.

Published on Feb. 26, 2026

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New research from the University of California, Riverside has uncovered biological clues that help explain why some bodies gain weight more easily on diets high in soybean oil. The study found that the answer may lie in how the liver handles certain fats at the molecular level, with a liver protein called HNF4α playing a key role. Mice genetically engineered to produce a slightly different version of HNF4α gained far less weight on a high-soybean oil diet compared to regular mice, due to differences in the production of fat-regulating compounds called oxylipins.

Why it matters

This research provides important insights into why weight gain can affect people unequally, even when they consume similar diets. It shows that liver metabolism plays a powerful role in how dietary fats influence health, which could guide more personalized nutrition advice in the future. The findings also raise questions about the health impacts of the dramatic increase in soybean oil consumption over the past century.

The details

In the study, most mice fed a high-fat diet rich in soybean oil gained significant weight, with their livers showing signs of stress and cholesterol levels increasing. However, a separate group of genetically engineered mice that produced a slightly different version of the HNF4α protein gained far less weight, despite eating the same diet. This difference was not due to how much food the mice ate, but rather what their bodies did with the fat once it entered the liver. The genetically engineered mice produced far fewer of the fat-regulating compounds called oxylipins, which have been linked to weight gain and liver fat buildup. They also showed stronger mitochondrial activity, allowing them to burn fuel more efficiently.

  • The study was conducted by researchers at the University of California, Riverside.
  • The findings were published in the Journal of Lipid Research in February 2026.

The players

Sonia Deol

A biomedical scientist at UC Riverside and corresponding author of the study.

Frances Sladek

A professor of cell biology at UC Riverside and co-author of the study.

HNF4α

A liver protein that plays a powerful role in metabolism by helping control hundreds of genes linked to how fats are processed.

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What they’re saying

“This may be the first step toward understanding why some people gain weight more easily than others on a diet high in soybean oil.”

— Sonia Deol, Biomedical scientist at UC Riverside (Journal of Lipid Research)

“It's not the oil itself, or even linoleic acid. It's what the fat turns into inside the body.”

— Frances Sladek, Professor of cell biology at UC Riverside (Journal of Lipid Research)

“Soybean oil isn't inherently evil. But the quantities in which we consume it is triggering pathways our bodies didn't evolve to handle.”

— Frances Sladek, Professor of cell biology at UC Riverside (Journal of Lipid Research)

What’s next

Researchers are now studying whether other oils high in linoleic acid, including corn, sunflower, and safflower oils, trigger the same internal reactions. They also want to understand exactly how oxylipins promote weight gain and whether those pathways can be safely interrupted.

The takeaway

This study offers important insights into the role of liver metabolism in how dietary fats influence health, providing a potential explanation for why weight gain does not affect everyone equally even on similar diets. The findings could guide more personalized nutrition advice and early detection of metabolic stress in the future, while also raising questions about the health impacts of the dramatic rise in soybean oil consumption over the past century.