The highest grade, however, provides the fullest and strongest flavor. Extra- virgin olive oil is pressed and processed without heat or solvents and ranges in color from gold to deep green. Some reports of canola oil on the Internet say it's hazardous to health. Though frying foods in fat wouldn't top the list of suggested modes of preparation, some oils cook more efficiently because they have a higher smoke point, or the temperature at which the oil begins to decompose and produce smoke. The highest smoke points belong to grapeseed and avocado oils, followed by safflower and sunflower oils, soybean, canola, corn and peanut, leaving sesame and olive oils more suited to salad dressings.
Heat also destroys the sensitive oils, such as almond, walnut and other fancy ones.
Olive oil contains the most unsaturated fat, as opposed to saturated. If a prepared salad dressing says it has no fat, it probably contains lots of sugar. The most healthful way to include oil in your diet is to use it sparingly. Use a nonstick pan and add the oil with a mister or sprayer. These can be purchased at kitchen product stores.