Cooking oil

Cooking oil is a liquid fat from plants or animals, used for frying, baking, and other cooking methods. Because it can get much hotter than water, it speeds up cooking, adds flavor, and spreads heat evenly, which helps prevent burning or uneven cooking. It can also add its own taste to food. Beyond heat-based cooking, it’s used cold in things like salad dressings and bread dips.

At room temperature, most cooking oils are liquid, but some high in saturated fat—like coconut, palm, and palm kernel oil—are solid. Plant-based options include olive, palm, soybean, canola (rapeseed), corn, peanut, sesame, and sunflower oils, plus other vegetable oils. Animal-based oils include butter, ghee, schmaltz, and lard. Oils can be flavored with herbs, chilies, or garlic, and cooking spray is simply oil in aerosol form.

**Health and nutrition** Eating small amounts of saturated fat is common, but research shows a strong link between high saturated fat intake and higher LDL cholesterol, which raises heart disease risk. Studies also suggest that swapping saturated fats for polyunsaturated fats lowers heart disease risk by about 10% for every 5% replacement. The Mayo Clinic warns that coconut, palm, and palm kernel oils are high in saturated fats. Healthier choices have less saturated fat and more unsaturated fats (especially omega-3s), like olive, peanut, canola, soy, and cottonseed oils. The US National Heart, Lung, and Blood Institute recommends replacing saturated fats with polyunsaturated and monounsaturated fats, naming olive and canola as good monounsaturated sources, and soybean and sunflower as good polyunsaturated sources. One study found non-hydrogenated oils like soybean and sunflower are better than palm oil for heart health. Nut-based oils like cashew oil are safe for people with nut allergies because oils are mostly fat, and allergic reactions come from proteins on the nut’s surface. Most cultivated plant seeds have more omega-6 than omega-3 fatty acids, except for a few. Seeds grown in colder climates tend to have higher omega-3 levels.

**Trans fats** Trans fats are not essential and offer no health benefits. They raise LDL cholesterol and lower HDL cholesterol, increasing coronary heart disease risk. Trans fats from partially hydrogenated oils are worse than naturally occurring ones. Large studies link high trans fat intake to heart disease and possibly other illnesses. The FDA, National Heart, Lung, and Blood Institute, and American Heart Association all advise limiting trans fats. In the US, trans fats are no longer considered safe without special permission, so they can’t be added to foods or cooking oils.

**Cooking with oil** Heating oil changes its properties quickly. Oils that are healthy at room temperature can become unhealthy when heated too high, especially if heated repeatedly. The risk comes from fatty acids oxidizing, and oils with more unsaturated fats oxidize faster in hot air. So, match an oil’s heat tolerance to your cooking temperature, and change frying oil a few times per week. Deep-frying temperatures are usually 170–190°C (338–374°F), sometimes lower at 130°C (266°F). Palm oil has more saturated fat than canola, corn, linseed, soybean, safflower, or sunflower oil, so it handles high heat and resists oxidation better than high-polyunsaturated oils. Since the 1900s, the food industry has added palm oil to products because it stays stable in deep frying and baking at very high temperatures, and it has natural antioxidants—though refined palm oil loses most of its orange-red carotenoids. Oils with high smoke points suitable for high-temperature frying include avocado, mustard, palm, peanut (called groundnut oil in the UK and India), rice bran, safflower, olive, semi-refined sesame, and semi-refined sunflower oils. For less aggressive frying, a good oil has a mild flavor, a smoke point of at least 200°C (392°F), a flash point of 315°C (599°F), and no more than 0.1% free fatty acids and 3% linolenic acid. Oils with more linolenic acid tend to polymerize or gum up, getting thicker with age. Olive oil resists heat damage and has been used for frying for thousands of years.

**Storing and keeping oil** All oils break down from heat, light, and oxygen. To slow rancidity, manufacturers often add a blanket of inert gas (usually nitrogen) to the storage container’s air space right after production—called tank blanketing. Stored in a cool, dry place, oils last longer but may thicken; they return to liquid if left at room temperature.