Seeding doubt: The truth about cooking oils

Bogus information about seed oils — especially canola oil and soybean oil — has been circulating on the Internet for more than a decade. The details are misleading, often creating confusion in the kitchen.

“Patients ask me if they need to avoid seed oils because they’ve seen social media claims that these oils are toxic and can promote all sorts of diseases,” says Alison Kane, a dietitian at Harvard-affiliated Massachusetts General Hospital. But these oils aren’t inherently unhealthy. It all depends on how you use them — that is, combined with which specific types of food — and how much you’re consuming.

What are seed oils?

Edible oils derived from plants are commonly known as cooking or vegetable oils. They include seed oils, which are extracted from the seeds of different plants. Common examples include canola, corn, soybean, sunflower, and safflower oils.

Seed oils contain mostly unsaturated fat, while fats from animal sources such as butter, cheese, and meat (as well as coconut and palm oils) contain mostly saturated fat. Decades of research shows that consuming unsaturated fat in place of saturated fat is linked to a lower risk of heart attack and death from heart disease.

Seed oils have other attributes; for example, canola oil is a decent source of alpha-linolenic acid (ALA), the main vegetarian source of essential omega-3 fatty acids. Like EPA and DHA (the omega-3 fats found in fatty fish), ALA has anti-inflammatory and other effects thought to benefit cardiovascular health. Canola oil also contains phytosterols, which are compounds that occur naturally in plants that may help lower cholesterol.

What’s the problem?

According to the critics, seed oils also have certain unsavory attributes. After seeds are crushed, their oil is extracted with hexane, a solvent that’s hazardous in gas form but evaporates during oil processing, leaving limited if any residual hexane in the liquid form.

Seed oils contain omega-6 fatty acids, including one called linoleic acid. Our bodies convert linoleic acid into arachidonic acid, a building block for molecules that can promote inflammation. Chronic inflammation plays a role in heart disease and other serious health problems.

Finally, soybean and canola oils are commonly used in fast food and other restaurant and prepared foods because they’re inexpensive. Repeatedly heating unsaturated oils up to high temperatures creates trans fats and other harmful substances. Factories and restaurants don’t change their oil often enough to get rid of those compounds, which likely contributes to the strong link between frequent fried food consumption and heart disease.

Hold on a second

While the complaints about seed oils seem valid, the claims deserve a second look.

Regarding hexane, for example, the average person’s intake of any possible residual traces of this chemical in oils and other foods is dwarfed by exposures from other sources, such as gasoline fumes.

What’s more, the dangerous compounds of heated seed oils in fast food are just one aspect of deep-fried fast foods like fries and chicken fingers. These foods also contain high amounts of fat, added sugar, salt, and calories. That’s also true of other common calorie sources in the average American diet. “Seed oils are hiding in our food supply, mainly in crunchy, salty, or sweet snack foods that come in a bag, like chips, crackers, cookies, and other baked goods,” Kane says.

Finally, the linoleic concerns aren’t backed by science. Research shows that increasing linoleic acid in the diet doesn’t increase levels of inflammatory markers in the blood.

What you should do

Kane says there’s no need to worry about those bottles of soybean, canola, and sunflower oils in your pantry. Using a few tablespoons to sauté vegetables or in a salad dressing is a healthy option. You can also replace all or part of the butter or margarine with canola or another mild-flavored seed oil in recipes for baked goods like muffins and cakes. It’s best to store seed oils in the refrigerator to preserve their flavor and freshness.

Eating lots of fast food and junk food is a real problem. However, Kane tells her patients that it’s fine to enjoy “fun food” such as French fries and other treats once in a while. The key is to consume seed oils — and all other sources of fat — in moderation.

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