The Little-Known Oil that Could be Causing Obesity

One of the most widely used vegetable oils in processed foods could be driving weight gain due to how the body metabolises it, according to new research.

Soybean oil is rarely used as a primary cooking oil but is common in products such as salad dressings, margarine, and crisps. Previous studies linked it to obesity, but the biological cause remained unclear.

Scientists at the University of California, Riverside, now suggest the issue is not the oil itself but how it is processed internally when consumed in excess.

Frances Sladek, professor of cell biology at the university, said:

“Soybean oil isn’t inherently evil.

“But the quantities in which we consume it is triggering pathways our bodies didn’t evolve to handle.”

Researchers fed two groups of mice a soybean-oil-rich diet to examine why it promotes obesity more than other fats. One group had no genetic changes, while the other produced a modified liver protein affecting fat metabolism.

The genetically unmodified mice gained significant weight, while the altered group did not. The findings suggest that genetics and modern diets interact to influence obesity risk.

Sonia Deol, a biomedical scientist at the university and corresponding author of the study, said:

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

The study builds on earlier research linking soybean oil to weight gain.

Professor Sladek continued: “We’ve known since our 2015 study that soybean oil is more obesogenic than coconut oil.

“But now we have the clearest evidence yet that it’s not the oil itself, or even linoleic acid. It’s what the fat turns into inside the body.”

Linoleic acid is a key fatty acid in soybean oil that the body converts into molecules called oxylipins. High intake increases oxylipin levels, which are linked to inflammation and fat accumulation.

The genetically engineered mice produced fewer oxylipins and showed healthier livers despite consuming the same high-fat diet.

They also displayed stronger mitochondrial function, which may explain their resistance to weight gain.

Researchers found these mice had sharply lower levels of two enzyme families that convert linoleic acid into oxylipins. No human trials are currently planned, but the team hopes the findings will shape future research and nutrition policy.

Professor Sladek added: “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 recognise the link between excessive soybean oil consumption and negative health effects.”