Soybean oil is the most widely used cooking oil in the United States and a major ingredient in many processed foods.
Now, a new study from the University of California, Riverside suggests that heavy consumption of soybean oil may contribute to obesity — at least in mice — through biological pathways scientists are only beginning to understand.
In the study, published in the Journal of Lipid Research, researchers fed mice a high-fat diet rich in soybean oil. As expected, most of the animals gained significant weight.
But one group of genetically engineered mice remained relatively lean, even though they ate the same food. The difference came down to how their bodies processed fat.
These mice produced a slightly altered version of a liver protein called HNF4α, which controls the activity of hundreds of genes involved in metabolism.
This alternative form of the protein appeared to change how the liver handled linoleic acid, a fatty acid that makes up a large portion of soybean oil.
“This may be the first step toward understanding why some individuals gain weight more easily than others when consuming a diet high in soybean oil,” said Sonia Deol, a biomedical scientist at UC Riverside and lead author of the study.
Linoleic acid itself is not stored directly as fat. Instead, the body converts it into signaling molecules known as oxylipins. When linoleic acid intake is high, oxylipin levels rise. Previous research has linked these molecules to inflammation and fat accumulation. In this study, regular mice on the soybean oil diet had high levels of oxylipins and developed obesity, while the genetically altered mice had far fewer oxylipins and healthier livers.
Interestingly, the protected mice also showed stronger mitochondrial function. Mitochondria are the cell’s energy producers, and better mitochondrial performance may help burn fat more efficiently, reducing weight gain even on a high-fat diet.
The researchers were able to pinpoint specific oxylipins derived from linoleic acid and another fatty acid in soybean oil, alpha-linolenic acid, that were required for weight gain in normal mice. However, oxylipins alone did not automatically cause obesity. Transgenic mice on a low-fat diet still had elevated oxylipins but did not gain excess weight, suggesting that obesity results from a combination of dietary fat, metabolic stress, and genetic factors.
Further analysis showed that the altered mice had much lower levels of enzymes that convert linoleic acid into oxylipins. These enzymes are found in all mammals, including humans, and their activity varies widely depending on genetics, age, sex, medications, and overall health. This variability could help explain why people respond differently to diets rich in soybean oil.
Another notable finding was that oxylipin levels in the liver — not in the blood — were linked to body weight. This suggests that standard blood tests may miss early metabolic changes happening inside organs.
Soybean oil consumption in the U.S. has increased dramatically over the past century, now accounting for nearly 10% of total calories. While soybean oil contains no cholesterol and soybeans themselves are nutritious, the researchers caution that consuming large amounts of linoleic acid, especially through ultra-processed foods, may push the body into unhealthy metabolic territory.
“Soybean oil isn’t inherently bad,” Deol said. “But the amount we’re consuming may be activating biological pathways our bodies never evolved to handle.”
Source: KSR.
