8 Popular Cooking Oils to Avoid, And Why

Oils are everywhere: we dress our salads with them, we drizzle our stir-frys with them, we dip our breads in them. We use them nearly every time we cook, bake, or roast. Unfortunately, most oils are heavily refined, which is to say stripped of both their culinary aspects and their nutrition. “Neutral” oils have no flavor, no aroma, and they’re all the same pallid yellow color.

Worse yet, refined oils have often been rendered rancid during processing, and you don’t want to eat rancid food—how many times have you sniffed milk or scrutinized cheese to make sure your food hasn’t gone bad?

Refined oils are made from ingredients (olives, nuts, seeds, etc.) that have been cleaned, crushed, steamed, pressed with high friction heat, extracted with solvent, distilled, bleached, deodorized, and steamed again. In short, they’ve been subjected to all of the factors that make oil go bad: heat, light, time, and chemicals.

Unrefined oils are made from ingredients that have been cleaned and quickly pressed in cold, dark environments, then immediately bottled to minimize their exposure to oxygen. In other words, unrefined oils are maximally fresh, with all of their flavor and nutrition intact. Unrefined oils are often sold in opaque glass bottles to shield them from light as they sit on store shelves.

Once you’ve compared the refined version of an oil to its unrefined version—say, a mainstream “light” olive oil compared to extra-virgin olive oil from California Olive Ranch—you’ll realize that unrefined oils taste, smell, and look like what they are made from. Extra-virgin olive oil tastes like olives. Unrefined peanut oil has an incredibly peanutty aroma. Unrefined pistachio oil is a lovely pale green. And once you’ve found the real deal, you’ll be hooked!

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We’ll talk about the best oils to have on hand in Part 2 of Know Your Oils, but here’s a quick guide to the type of oils that are commonly refined.

Canola oil
This now-common oil used to be known as rapeseed oil and was used as lamp fuel and in industrial applications. A more digestible version was bred in Canada in the 1970s, and since then, rapeseed has become widely grown for oil. In 1995, a GMO version of canola was introduced, and these days nearly all canola is genetically modified as well as being heavily refined.

Soybean oil
Soybeans have long been used to make “vegetable” oil, so-called because then producers can interchange one oil for another without having to change the packaging to reflect the contents. Soy is another major GMO crop and is almost always heavily refined.

Cottonseed oil
Not surprisingly, this oil goes hand-in-hand with cotton production. In addition to often being a GMO, cottonseed oil has historically been hydrogenated (i.e., made into trans fats) to make shortenings like Crisco.

Corn oil
This rounds out the list of the most commonly found GMO oils. Since corn oil is primarily composed of polyunsaturated fatty acids, it’s very fragile and is easily damaged by heat-intensive processing. Unfortunately, nearly all corn is subjected to heavy refinement.

Sunflower oil
While sometimes gently treated and cold-pressed into a nutty, buttery oil, more often sunflower oil is heavily refined and used to make products like margarine. It’s also very inflammatory, with almost 3,000 mg of omega-6 fats in a single teaspoon of sunflower oil (and 0 mg of anti-inflammatory omega-3 fats).

Safflower oil
Long been cultivated around the world, in part because its flowers can be used as textile dyes, the safflower yields an oil that is almost always heavily refined and doesn’t have a favorable inflammatory/anti-inflammatory fat ratio: 1 teaspoon of safflower oil contains over 650 mg of omega-6 fats and 0 mg of omega-3 fats.

Grapeseed oil
A go-to for chefs who like its high smoke point, grapeseed oil is a waste byproduct of winemaking. It’s also high in polyunsaturated fats—it’s almost 70 percent polyunsaturated—which means that grapeseed oil is very delicate and easily rendered rancid during processing. And like sunflower oil, grapeseed oil also has about 3,000 mg of inflammatory omega-6 fats per teaspoon (with about 5 mg of anti-inflammatory omega-3 fats).

Olive oil that isn’t extra-virgin
Many olive oil products have been heavily refined. Terms to watch out for include light, extra-light, virgin, pure, natural, pomace, and anything else that doesn’t say “extra-virgin.” Word to the wise: Even when an olive oil is marked “extra-virgin,” it may not be—it may be just as refined as the vegetable oil sitting next to it. Tom Mueller explored the subject in great detail in his 2011 bestseller Extra Virginity: The Sublime and Scandalous World of Olive Oil. Check out his website for the scoop on olive oil, or go with the results of the UC Davis Olive Center’s 2011 study that found California Olive Ranch to consistently score perfect marks across the board—their extra-virgin olive oil really is extra-virgin. Find more info and recommendations from UC Davis’ Olive Center here.

Lisa Howard is the author of the recently released The Big Book of Healthy Cooking Oils, which offers over 80 recipes featuring unrefined oils and fats.

Photo by Martin Cooper CC BY