Is Soybean Oil Bad for You?

Soybean oil, the most commonly produced edible oil used for frying fast foods, added to packaged foods, and fed to livestock, may very well be unhealthy.

Soybean oil, the most common fat in the American diet, is very bad for mice. Does that mean it isn’t healthful for you and your family?

Researchers at the University of California, Riverside (UCR), have been studying the effects of the oil on mice for more than a decade. They have found evidence that it affects the hypothalamus. The hypothalamus is the part of your brain that regulates your body weight and temperature, as well as reproduction and responses to stress.

For example, in mice fed soybean oil, levels of oxytocin, the chemical that helps humans form bonds with others, fell.

The research suggests that soybean oil may play a role in obesity, diabetes, and neurological conditions like autism, Alzheimer's disease, anxiety, and depression. 

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Americans consume about 40 percent of their calories in fat, much of it from soybean oil. In previous research, the team fed mice one of two diets containing that much fat.

One group of mice ate coconut oil, which is mostly a saturated fat. In diet number two, half the fat came from soybean oil, the main ingredient in vegetable oil. This diet was similar to what Americans eat. The two diets contained the same number of calories.

Mice eating foods with soybean oil — which is so plentiful in the American diet — ended up gaining almost 25 percent more weight than the coconut-oil eaters. They accumulated more fat and were more likely to develop fatty livers, diabetes, and insulin resistance, all contributors to metabolic syndrome.

It may sound odd that coconut oil, a saturated fat, would be better for you. Studies in the 1950s and 1960s linked eating saturated fats to heart disease, and Americans were told to cut back on meat and dairy products and get fat from plants instead.

But evidence is growing that coconut and palm oil, which contain a different kind of saturated fat, may help prevent and even treat metabolic syndrome.

Soybean oil could be a bigger problem in your diet than sugar. In the study, two other sets of mice also ate about the same amount of fructose as Americans consume.

Again, the mice consumed the same amount of calories in each of the diets, allowing researchers to compare the impact of the food itself.

Mice who ate fructose gained 12 percent more weight than those on the coconut oil. But they did better than those who ate soybean oil.

"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, PHD, a postdoctoral cell biologist.

That doesn’t mean you should eat more sugar — but it does suggest that you should cut back on vegetable oil, which you’ll find in processed foods, margarine, salad dressings, and snacks.

It also doesn’t mean you should avoid all soy products, which may contain low amounts of oil.

Should you run out and buy coconut oil? Not so fast.

The benefits of coconut oil remain controversial. On the other hand, olive oil has emerged as a winner in many studies. For example, one large study found that consuming olive oil reduced heart disease and death in a population at high risk for heart problems.

The clearest message here is to limit your consumption of soybean oil and vegetable oil.

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