Khaberni - A recent American study has found that soybean oil, the most consumed cooking oil in the United States and a staple in processed foods, contributes to obesity, at least in mice, through a mechanism that scientists are now beginning to understand.
In an experiment conducted at the University of California Riverside, most of the mice following a high-fat diet rich in soybean oil gained significant weight. However, this did not happen for a group of genetically modified mice.
These mice produced a slightly different form of liver protein that affects hundreds of genes associated with the metabolism of fats. It also appears that this protein alters how the body processes linoleic acid, a main component in soybean oil.
Sonia Deol, a biomedical scientist at the University of California Riverside and the corresponding author of the study published in the Journal of Lipid Research said, "This could be the first step towards understanding why some people gain weight more easily than others when following a diet rich in soybean oil."
In humans, there are two types of liver protein HNF4α, but usually only the alternative form is produced under certain conditions, such as chronic disease or metabolic stress from fasting or alcoholic fatty liver. This difference, along with differences in age, sex, medications, and genes, may help explain why some people are more susceptible than others to the metabolic effects of soybean oil.
The study builds on previous work by researchers at the University of California Riverside, linking soybean oil to weight gain. Frances Sladek, professor of cell biology at the University of California Riverside said, "Since our study in 2015, we've known that soybean oil causes more obesity than coconut oil. But now we have the clearest evidence yet that the problem is not the oil itself, or even linoleic acid, but what the fats turn into inside the body."
Linoleic acid turns into molecules called oxylipins. Excessive consumption of linoleic acid can lead to increased amounts of oxylipins, which are associated with inflammation and fat accumulation.
Genetically modified mice in the study showed a significant decrease in oxylipins and a healthier liver despite following the same soybean oil-rich diet as regular mice. Notably, they also showed improvement in mitochondrial functions, which may explain their resistance to weight gain.
Researchers narrowed down the compounds linked to obesity to specific types of oxylipins derived from linoleic acid and alpha-linolenic acid, another fatty acid found in soybean oil. These oxylipins were necessary for weight gain in regular mice.
Oxylipins
However, genetically modified mice on a low-fat diet also showed high levels of oxylipins without becoming obese, suggesting that the presence of these molecules alone is not sufficient, and likely that other metabolic factors contribute to obesity.
Further analysis revealed that genetically modified mice had significantly lower levels of two main families of enzymes responsible for converting linoleic acid into oxylipins. Notably, the function of these enzymes is highly conserved among all mammals, including humans. It is known that levels of these enzymes vary greatly based on genetic factors, diet, and other factors.
The team also noted that oxylipin levels in the liver only, not in the blood, are linked to body weight. This means that common blood tests may not reliably capture early metabolic changes related to diet.
Consumption of soybean oil in the United States has increased fivefold in the past century, from about 2% of total calories to nearly 10% today. Although soy is a rich source of plant protein and its oil contains no cholesterol, excessive consumption of linoleic acid, including from ultra-processed foods, can fuel chronic metabolic conditions.
In addition, despite the lack of cholesterol in the oil, a study by the University of California Riverside found that consumption of soybean oil is associated with elevated cholesterol levels in mice.
Researchers are now exploring how oxylipin formation causes weight gain, and whether similar effects occur with other oils rich in linoleic acid, such as corn, sunflower, and safflower oils.
Sladek said, "Soybean oil isn't inherently evil.. But the amounts we consume stimulate pathways that our bodies weren't evolved to handle."
Although no human trials are planned, the team hopes these findings will guide future research and inform nutrition policy. Sladek said, "It took 100 years from the first observation of the relationship between chewing tobacco and cancer until warning labels appeared on cigarettes. We hope it doesn't take as long for society to realize the relationship between excessive consumption of soybean oil and negative health impacts."
