The healthiest oils are those that are high in monounsaturated and polyunsaturated fats, such as vegetable oil and olive oil. These types of fats can help lower your risk of heart disease when used instead of saturated and trans fats.
When it comes to cooking, however, not all oils are created equal. Some oils can handle the heat, and some can't.
An oil's smoke point is the temperature at which it will start to smoke and break down. When cooking oil starts to smoke, it can lose some of its nutritional value and can give food an unpleasant taste.
Oils with high smoke points, such as corn, soybean, peanut and sesame, are good for high-heat frying and stir-frying. Olive, canola and grapeseed oils have moderately high smoke points, making them good for sauteing over medium-high heat.
Oils with low smoke points, such as flaxseed and walnut, are best saved for use in salad dressings and dips.