US cooking oil and obesity: A common kitchen staple may be doing more than simply adding flavour and calories to the body. A new study in the Journal of Lipid Research reports that soybean oil, the most widely used cooking oil in the United States, could directly promote weight gain in mice, and the effect appears to be linked to how the body handles one of its major fatty acids.
Scientists focused on linoleic acid, an omega-6 fat that makes up a large share of soybean oil. In the body, linoleic acid is broken down into compounds called oxylipins. When linoleic acid intake is high, levels of these oxylipins rise. In the new study, researchers found that certain oxylipins were strongly associated with obesity in mice fed a soybean-oil-rich diet.
“This may be the first step toward understanding why some people gain weight more easily than others on a diet high in soybean oil,” said Sonia Deol, a biomedical scientist at the University of California, Riverside, and the study’s corresponding author.
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To probe cause and effect, the team used a line of genetically engineered mice that carries an altered version of a liver regulatory gene, P2-HNF4α. This genetic tweak alters several metabolic pathways, including reducing the activity of several enzyme families that normally convert linoleic acid into oxylipins. These enzymes are present in all mammals, including humans, and their activity can vary from person to person depending on genetics, diet and other influences.
Both the modified mice and normal mice were then fed a diet high in soybean oil. By the end of the experiment, the genetically altered animals gained significantly less weight and had healthier livers than the normal mice, even though their diets were the same. The researchers identified specific oxylipins derived from linoleic acid and alpha-linolenic acid (another fatty acid found in soybean oil) that were elevated in the obese mice and closely linked to fat gain.
The findings suggest that the way the body metabolises linoleic acid may be a key factor in soybean oil’s contribution to fat accumulation. In other words, the potential problem may not lie solely in the oil’s calorie content, but in the bioactive molecules produced when its fatty acids are processed.
The authors stress that the work was carried out entirely in mice and cannot be directly translated to human obesity.
Still, the study raises questions about whether diets high in linoleic-acid-rich oils such as soybean oil, which is widely used in restaurants, packaged foods, snacks and fried items because of its low cost and neutral taste, might influence body weight through biochemical pathways beyond simple “calories in, calories out.” The researchers say more work in humans will be needed to understand how these mechanisms play out in real-world diets.