This 'Healthy' Oil Could Lead to More Weight Gain Than Sugar

Sugar has been blasted in recent years for its link to obesity and a slew of health problems, but now experts say the food world has a new problem child: Soybean oil.

Soybean oil, considered a “healthier” alternative to some oils that contain more saturated fat, actually leads to more weight gain than fructose, according to new research on mice that was published in the journal PLOS One.

For their research, scientists divided the mice into four groups and fed them each a different diet that contained 40 percent fat (similar to the average American diet). One diet used coconut oil (which largely consists of saturated fat), another used half coconut oil and half soybean oil (which primarily contains polyunsaturated, or “good” fat). The third and fourth diets had fructose added.

All four diets had the same number of calories, and the mice were fed the same amount of food.

Here’s what researchers discovered: Mice that were on the soybean oil diet gained 12 percent more weight than those that ate a fructose diet, and 25 percent more weight than mice on the coconut oil diet.

The mice on the soybean oil diet also had larger fat deposits in their bodies and fatty livers, and were more likely to have developed diabetes and insulin resistance. Mice on the fructose diet didn’t get off easy, either — they had similar issues, but to a less severe degree.

And, it’s worth noting, the amount of soybean oil the mice ate was similar to what we get in our diets.

Oils from plants — including soybean oil — have gained popularity after research linked the saturated fats in butter to an increased risk of heart disease. While the American Heart Association specifically recommends using olive, canola, corn, and safflower oils for heart health, soybean oil is also popularly used. 

So you say you don’t cook with soybean oil? That doesn’t mean you’re not ingesting it: Soybean oil shows up in our margarines, processed foods, salad dressings, and snacks, among other things. And, despite its polyunsaturated fat, that’s not a great thing, says certified dietitian-nutritionist Lisa Moskovitz, RD, CEO of NY Nutrition Group.

The study’s researchers aren’t sure why soybean oil led to more weight gain than sugar, but Moskovitz tells Yahoo Health that soybean oil’s high omega-6 fatty acid content could be part of the problem. But Moskovitz says the oil “could also have metabolic effects that can interfere with hormone regulation, fat burning, and appetite control,” leading you to eat more of it while feeling less full.

It could also be a matter of calories alone, certified dietitian-nutritionist Jessica Cording tells Yahoo Health. Soybean oil is a fat, and fats contain nine calories per gram, she says. However, carbohydrates such as fructose contain four calories per gram. 

While the study only looked at soybean oil on its own, Moskovitz 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 our biggest sources of soybean oil.

If you’re shopping for an oil to use at home, Cording recommends taking a pass on soybean oil and reaching for olive oil, which is versatile and rich in healthy monounsaturated fats.