It only takes a trip to the supermarket to figure out that all cooking oils aren’t created equal. Dozens of bottles crowd the shelves: There’s oil made from olives and corn and seeds and soybeans and nuts. Some are flavored and fancy; many are popular abroad, particularly in Asia, the Mediterranean, and the Middle East. Oils differ not only in origin but also in the type of fat they contain and how they’re used in the kitchen. Familiarizing yourself with your options is part of the fun of cooking, since an oil’s flavor plays a major role in the taste of your food.
For starters, it’s useful to consider how different oils are made. Some are extracted from seeds with the use of solvents and high temperatures that can damage the oil and alter its chemical makeup. Others are pressed mechanically (sometimes called “cold pressed”) at temperatures under 120 degrees and without the use of additional heat or chemicals. Corn oil, for instance, is often highly processed while flaxseed oil and extra virgin olive oil are created using minimal heat.
Once an oil has been pressed—whether manually or with the use of chemicals—it often goes through a refining process. The more processing an oil undergoes, the higher its smoke point: the temperature at which it starts to smoke. “Most oils do break down,” says Julie Logue-Riordan, a chef and cooking instructor in Napa, Calif. “The higher the temperature is, the more they break down.” And that means a loss in flavor, in addition to the risk of a kitchen fire. Oils with high smoke points (like sunflower, safflower, and peanut oils) can withstand high heat and are well suited for frying or sautéing. Those with low smoke points (such as flaxseed, extra virgin olive oil, and many nut oils), however, are best used over low heat. Some oils are minimally processed, may appear cloudy, and are best used unheated, such as in dressings.
In addition to determining how it is used, an oil’s level of processing also plays a role in its nutritional value. “There is a nutritional difference the purer the product,” says Robin Plotkin, RD, LD, a dietitian in Dallas. “The least amount of processing that happens, the better it is for you, as with other foods.”
The Inside Story
Processing method is only part of what differentiates one oil from the next. The other factor: the type of fat an oil contains.
Like butter, lard, and red meat, some cooking oils are high in saturated fat, which can raise LDL (“bad”) cholesterol levels, which is believed to up your risk for heart disease and stroke. Palm and palm kernel oils both have high levels of saturated fat and are best avoided. Coconut oil is the highest in saturated fat of all common oils.
What happens when you turn liquid cooking oil into a solid? That’s what scientists wondered when they added hydrogen atoms to unsaturated fat, such as vegetable oil. The result: partially hydrogenated oil. The oil stood up to high heat without breaking down, was solid at room temperature, and was cheaper—all of which made it seem like the perfect addition to packaged foods. Today, however, we know partially hydrogenated oils as trans fats, which can increase LDL (“bad”) cholesterol and increase the risk for heart disease.
A better choice is monounsaturated fats, which are “tied to lowering our blood cholesterol and triglycerides,” says Plotkin. “Those are the ones we like to use for people who have heart disease or who are at risk for heart disease.” Canola, peanut, and olive oils are among those that contain monounsaturated fats. Less often used but fun to try are avocado and macadamia nut oils. For ideas on how to use them, see the recipes here, here, and here.
• Canola oil has a neutral flavor and cooks well at high temperatures. Use it for frying or sautéing as well as for baking.
• Peanut oil adds a mild nutty flavor to foods and can also withstand high temperatures. It’s typically used for stir-frying since the flavor meshes well with Asian sauces.
• Olive oil’s flavor depends on how it’s made. The label should give a clue: Extra virgin olive oil has not been chemically processed, and has a richer flavor than other olive oils—which you pay for. If a label doesn’t say “virgin” or “extra virgin,” the oil may have been processed; it will have a lighter taste and be better suited to high-heat cooking. Since virgin olive oil can break down at high temperatures, it’s best used cold, whisked into dressings or drizzled over cooked fish or chicken to add extra flavor.
Polyunsaturated fats, like monounsaturated ones, can lower cholesterol and triglyceride levels, and reduce the risk of heart disease. They also contain omega-3 and omega-6 fatty acids, which the body can’t make on its own. “We as Americans get plenty of omega-6s in our diet due to the amount of processed foods that we consume,” says Plotkin. So if you use oils that are high in omega-6s (such as flaxseed, walnut, sunflower, safflower, grape seed, and corn oils), you’ll want to decrease the amount of processed foods you eat and vary the type of oils you use, picking a good mix of poly- and monounsaturated fats.
• Flaxseed oil is a top source of omega-3 fatty acids, which means it’s best suited for cold use. “The polyunsaturated fats that have those omega-3s can easily be damaged if they’re exposed to high heat,” says Plotkin. To maintain the nutritional value, use flaxseed oil in salsa or dressings, or drizzle it over cooked fish.
• Walnut oil is also high in omega-3s and has a mild, nutty flavor. “Walnut oil goes so nice with so many salads,” says Logue-Riordan. She uses it in dressings or as a finishing oil for a flavor boost.
• Sunflower oil is ideal for cooking since it can withstand high temperatures and has a neutral flavor. “I find that very versatile,” says Logue-Riordan, who em-ploys sunflower oil as an all-purpose oil. “It’s light, it’s flavorful. It really lets the ingredients shine through. I want something that’s not going to be competing with my vegetables.”
• Safflower oil has a mild flavor and a high smoke point, making it a good choice for frying and sautéing.
• Grape seed oil is another good choice for high-heat cooking. Like sunflower oil, grape seed has a neutral flavor suitable for most dishes.
• Sesame oil, when unrefined, has a deep flavor favored in many Asian dishes and works well in sauces and dips. The refined versions are suitable for cooking over high temperatures, such as in stir-fries.
• Corn oil is neutral-flavored and ideal for high-heat cooking. Though it’s a polyunsaturated fat, it’s often highly refined.
• Vegetable oil may be a single, unnamed oil or a blend of a variety of oils, such as corn, soybean, and sunflower. The label may not list the specific type of oils, but most vegetable oils work well at high temperatures. Since the flavor is bland, vegetable oil isn’t a top choice for dressings or dips.
How you store your oils makes a difference to their flavor and nutritional value, too. “Once an oil is open, you really need to use the oil within six months,” says Logue-Riordan. “You want to keep them away from heat and light. They will break down and go rancid really quickly.” You’ll know an oil is rancid when it smells and tastes “off.” Logue-Riordan keeps some delicate oils, such as nut oils, in the refrigerator to maintain freshness. If you have room in the fridge, all oils last longer when refrigerated; just let them come to room temperature (and thin out) before using.
And keep in mind that regardless of their health benefits, oils are still fat. “A tablespoon of oil, regardless of where it comes from, is right around 120 calories,” says Plotkin. “In that tablespoon, it is purely fat. Yes, it could be a healthy fat that you’re using, but it is fat.” Portion size is key, so use measuring spoons when mixing up salad dressing or even when drizzling some oil over a cooked meal. “We often under-guesstimate our calories and the amount we’re actually pouring into something or onto something,” Plotkin says. But as long as you keep serving size in mind, a good cooking oil can take your meal to the next level.