Soybean oil has become widespread in our diets in recent times – we're now consuming about 1,000x more of it than we were a century ago, due to its use as a cooking oil and as an ingredient in processed foods – and researchers have some serious concerns about how that might be affecting our health.A study published in the Journal of Lipid Research looks particularly at linoleic acid, an essential fat and the major component of soybean oil, and how it might be related to obesity and changes in the body's metabolism (energy-producing processes).In the study, led by a team from the University of California, Riverside (UCR), groups of mice were fed for several months with either a soybean oil diet (high in linoleic acid), a high-fat coconut oil diet (low in linoleic acid), or a low-fat diet.However, there was a twist: Some of the mice were genetically engineered to produce a different form of a liver protein crucial in processing fats.The normal mice on the high-fat soybean oil diet gained weight as expected, but the mice carrying the genetic tweak didn't, despite being on the same diet. It's compelling evidence that the liver protein, called HNF4α, is key to the link between soybean oil and obesity."This may be the first step toward understanding why some people gain weight more easily than others on a diet high in soybean oil," says biomedical scientist Sonia Deol, from UCR.