San Diego, CA--A new soybean oil genetically modified to be healthier than conventional soybean oil causes obesity, pre-diabetes and fatty liver in a nearly identical manner to that of regular soybean oil when part of a typical American high-fat diet, an animal study shows. The study results will be presented Friday at The Endocrine Society's 97th annual meeting in San Diego.
The recently introduced high-oleic soybean oil (Plenish, from DuPont Pioneer) had not been tested for long-term metabolic effects until this study, said the senior investigator, Frances Sladek, PhD, a professor of cell biology at the University of California, Riverside (UCR).
"While genetic modification of crops can introduce new beneficial traits into existing crops, the resulting products need to be tested for long-term health effects before anyone makes assumptions about their impact on human health," Sladek said.
Marketing for the new soybean oil claims it has 0 grams of unhealthy trans fat and more of the heart-healthy monounsaturated fats, as well as a longer shelf life. It has high levels of oleic acid and low levels of linoleic acid, a polyunsaturated fat, which Sladek said is similar to the fatty acid composition of olive oil.
Traditional soybean oil, which contains about 55 percent linoleic acid, is the most common oil consumed in the U.S. diet, and its use has increased remarkably since the 1970's, according to a study from the National Institutes of Health. Processed soybeans are the world's second largest source of vegetable oil, according to the U.S. Department of Agriculture.
In a previous study, Sladek's postdoctoral fellow Dr. Poonamjot Deol found that mice fed soybean oil as part of a high-fat diet had higher rates of obesity, diabetes, insulin resistance (an inability to efficiently use the hormone insulin) and fatty liver than did mice on a diet high in saturated fat from coconut oil.
In the new study, the researchers gave four groups of mice (12 mice in each group) different diets for six months. The control group received a low-fat diet, in which 5 percent of daily calories were from fat. The other groups received a diet with 40 percent of daily calories from fat, which Sladek said is an amount common in the American diet. One diet was high in saturated fat from coconut oil, and one had 41 percent of the saturated fat replaced with regular soybean oil. The last group had 41 percent of the saturated fat replaced with the genetically modified high-oleic soybean oil.
Mice fed a diet with either of the soybean oils had worse fatty liver, glucose intolerance and obesity than the group that got all their fat from coconut oil, the investigators reported. However, the mice whose diet included the high-oleic soybean oil had less fat tissue than the animals that ingested regular soybean oil. These mice weighed about 30 percent more than the controls that ate a low-fat diet, while the group on the diet containing regular soybean oil weighed 38 percent more than controls. The mice on the diet that was primarily coconut oil weighed only about 13 percent more than controls. Unlike the diet with regular soybean oil, the diet with the new high-oleic soybean oil did not lead to insulin resistance, according to Sladek.
"The genetically modified soybean oil does seem to have fewer negative metabolic consequences than regular soybean oil in mice, but it may not necessarily be as healthy as olive oil, as has been assumed by its fatty acid composition, and it is certainly less healthy than coconut oil which is primarily saturated fat," Sladek said.
UCR and the NIH-supported West Coast Metabolomics Center at UC Davis funded this research, which will be presented at the meeting by Deol, assistant project scientist at UCR who was supported by a National Institute of Environmental Health Sciences training grant.
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