According to scientists from the University of California, Riverside, a diet high in soybean oil may cause more obesity and diabetes than a diet high in fructose. Their study was published in the journal PLOS ONE on July 22.

The obesity epidemic in the United States is driving scientists to conduct more studies to determine precisely what causes this public health hazard. Specialists in the matter are focusing more than ever on fat, naturally, but also on fructose, a sugar commonly found in soda and processed foods.

Also commonly found in processed foods, margarines, vinaigrettes and snacks is soybean oil. And, in the US, consumption of soybean oil has considerably increased over the course of the last four decades. It represents 60% of edible oil consumed today, making it increasingly urgent for specialists to determine its link to weight gain and diabetes.

A team of scientists from the University of California, Riverside, under the direction of Poonamjot Deol, the assistant project scientist who directed the project in the lab of Frances M. Sladek, a professor of cell biology and neuroscience, attempted to determine which of three nutrients -- fructose, coconut oil and soybean oil -- was the most dangerous in terms of leading to obesity and diabetes.

The scientists fed male mice a series of four diets that contained 40 percent fat, similar to what Americans currently consume. In one diet the researchers used coconut oil, which consists primarily of saturated fat. In the second diet about half of the coconut oil was replaced with soybean oil, which contains primarily polyunsaturated fats and is a main ingredient in vegetable oil. That diet corresponded with roughly the amount of soybean oil Americans currently consume.

The other two diets had added fructose, comparable to the amount consumed by many Americans. All four diets contained the same number of calories and there was no significant difference in the amount of food eaten by the mice on the diets. This allowed the researchers to study the effects of the different oils and fructose in the context of a constant caloric intake.

The results of the study, published in the journal PLOS ONE, indicated that the mice on the soybean oil-enriched diet gained almost 25 percent more weight than the mice on the coconut oil diet and 9 percent more weight than those on the fructose-enriched diet. And the mice on the fructose-enriched diet gained 12 percent more weight than those on a coconut oil rich diet.

"This was a major surprise for us -- that soybean oil is causing more obesity and diabetes than fructose -- especially when you see headlines everyday about the potential role of sugar consumption in the current obesity epidemic," explained Professor Deol in a press release.

Furthermore, among the mice in the soybean oil group, the scientists noticed damage to the liver, a higher rate of diabetes and a resistance to insulin that was not present in the mice from the coconut oil group.

Finally, the study also showed that fructose had less severe metabolic effects than soybean oil, although it did present greater risk for the kidneys.