Most people think that fat is bad, but good quality oil is an essential part of a healthy diet. The best oils are pressed from seeds, grains, fruits or nuts at low temperatures and then minimally filtered. Rich in color, sometimes cloudy in appearance, they have the aroma and flavor of the whole food they were extracted from. They also contain antioxidants and many nutrients unlike highly processed fats. Unrefined sesame, peanut, grape seed and corn oils, and virgin olive oils are best for cooking because they can take high heat. They contain Omega3, Omega6 and Omega9 linoleic acids. Their rich aromas and flavors enhance the foods you prepare, reduce cholesterol and produce proper levels of hormones, help balance skin oils, promote healthy nerve cells and strong blood vessels. Other healthy oils such as walnut, hazelnut, almond and safflower oil should not be used in cooking with heat, but make wonderful sauces and dressings.
Most of these oils should last several weeks in the refrigerator after opening. Walnut and hazelnut tend to spoil quickly, even when refrigerated, so use them within a week or so. Olive oil is fine at room temperature.
Most of the fats and oils used in commercial cooking and on supermarket shelves are highly processed - they are defoamed with methyl silicone, washed in a caustic solution of lye and soap that removes essential fatty acids, bleached with hydrochloric or sulfuric acid, and deodorized with chemicals like BHT, BHA. These fats and oils have no flavor, have no nutrients, they are just grease. They are cheap and may last a long time on the supermarket or cupboard shelf but they are difficult for your body to process. Some oils are hydrogenated to make them solid at room temperature, like margarine, Crisco, etc., which may make fast foods crispy, but they clog up your arteries. Heart disease, cancer, diabetes, obesity and acne are just some of the unhealthy effects of highly processed fats and oils.
So go to the Natural Foods section of your grocery store, or to a health food store, or a good ethnic grocery and look for unrefined on the label. Look for intense color and expect wonderful aroma and taste from your oil. Expect to spend more on good quality.