New study: soybean oil may contribute to obesity – not only because of the calories

A new study published in the Journal of Lipid Research raises the possibility that soy oil may be related to obesity – not only because of its caloric value, but because of the way the body processes one of its main components.

As part of the study, researchers fed mice a diet high in soybean oil and examined how their bodies break down linoleic acid – an omega-6 fatty acid that is a significant part of the oil’s composition. The linoleic acid is broken down in the body into molecules called oxylipins, and when it is consumed in high quantity – the levels of oxylipins rise accordingly.

Genetic experiment: what happens when the process is disrupted

To examine the mechanism of obesity, the researchers asked a focused question: Will mice whose body’s ability to convert linoleic acid to oxylipins is limited – gain less weight even when fed a diet rich in soybean oil?

For this purpose, a genetically modified strain of mice was used, in which a modified version of a regulatory gene in the liver called P2-HNF4α operates. The genetic change reduced the activity of some of the enzyme families responsible for converting linoleic acid into oxylipins – enzymes that are also present in other mammals, including humans.

The researchers fed both the transgenic mice and normal mice a diet high in soybean oil. At the end of the experiment, it was found that the transgenic mice gained less weight and suffered from a healthier liver condition, compared to the normal mice that received the same diet.

Not just calories – but the decomposition products

The researchers identified specific oxylipins derived from linoleic acid and alpha-linolenic acid (another fatty acid in soybean oil), which were found at particularly high levels in mice that developed obesity. This finding strengthens the hypothesis that it is not only the amount of calories that determines, but also the biochemical products that are formed after processing the fatty acids in the body.

According to the researchers, the findings indicate that the internal processing of linoleic acid may play a central role in fat accumulation – beyond simple energy balance considerations.

The study was conducted entirely in mice, and the researchers emphasize that human metabolism is more complex. In addition, the genetically modified mice express particularly low levels of certain enzymes, which allows the mechanism to be examined more sharply – but also limits the ability to extrapolate the findings directly to humans. According to the researchers, the study does not establish that soybean oil necessarily causes obesity in humans, but suggests a biochemical mechanism that may explain why a diet high in oils rich in linoleic acid is linked to weight gain in animal models.