Sugar has come under a lot of criticism in recent years for its link to obesity and a number of health disorders, but as a new study reveals, the culprit should be tracked down elsewhere.
Namely, scientists at the University of California, Riverside, discovered that a diet high in soybean oil can contribute more to obesity and diabetes than a diet high in fructose, a sugar commonly found in soda and processed foods. The paper, “Soybean oil is more obesogenic and diabetogenic than coconut oil and fructose in mouse: potential role for the liver,” was published on July 22 in the journal PLOS ONE.
For their research, the scientists fed mice a series of four diets that contained 40% fat, which corresponded to the average American diet. The first diet used coconut oil, which largely consists of saturated fat. In the second diet about half of the coconut oil was substituted for soybean oil, which contains primarily polyunsaturated fats and is the key ingredient in vegetable oils. This diet resembled roughly the amount of soybean oil Americans consume at present. The third and fourth diets had fructose added; and again the amount added was similar to what the average American consumes today. All four diets had the same number of calories, and the mice were fed the same amount of food. In this way, the scientists could look at the effects of the different oils and fructose in the context of a constant caloric intake.
The findings revealed that mice that were on the soybean oil diet gained 12% more weight than those on a fructose diet, and 25% more weight than mice on the coconut oil diet.
Plus, the mice on the soybean oil diet also had larger fat deposits in their bodies, a fatty liver with signs of injury, diabetes and insulin resistance, all of which are part of the Metabolic Syndrome. Fructose in the diet produced less severe metabolic effects than soybean oil though it had more negative effects in the kidney and a noticeable increase in prolapsed rectums, a symptom of inflammatory bowel disease (IBD), which like obesity is on the rise. Mice on the fructose diet had similar issues, but to a less severe degree.
“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,” said Poonamjot Deol, the assistant project scientist who directed the project in the lab of Frances M. Sladek, a professor of cell biology and neuroscience.
Oils from plants — including soybean oil — became widely popular following the results of studies in the 1960s that linked saturated fatty acids in meat and dairy products to an increased risk of heart disease. Instead, polyunsaturated fatty acids found in plant oils have been promoted in nutritional guidelines. This new trend entailed an increase in the cultivation of soybeans in the United States, which has led to a significant rise in the consumption of soybean oil, found in processed foods, margarines, salad dressings and snack foods. Today, soybean oil accounts for 60% of edible oil consumed in the United States. That increase in soybean oil consumption is a reflection of the rise in obesity rates in the United States in recent decades.
The American Heart Association specifically recommends using olive, canola, corn, and safflower oils for heart health; however, soybean oil is also popularly used.
While the study only looked at soybean oil on its own, Liza Moskovitz, a certified dietitian-nutritionist, RD, CEO of NY Nutrition Group, points out that many products that contain the oil are also high in calories and sugar, which can add to even more weight gain. However, Moskovitz assures that soybean oil is fine when consumed in moderation — especially the new high oleic soybean oil, which is considered “slightly healthier.” It’s just a good idea to avoid eating processed foods, she says, which are the biggest sources of soybean oil.
The UC Riverside researchers also did a study with corn oil, which induced more obesity than coconut oil but not to the same degree as soybean oil. They are currently doing tests with lard and olive oil. They have not tested canola oil or palm oil.
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