Coconut oil tops the list as the best oil for cooking, followed by olive oil and avocado oil. Fish and flax oil are the worst options for cooking and should never be heated.
Coconut oil is perfect for high heat cooking and doesn't burn easily, because it is composed primarily of saturated fat. It's also an excellent choice for cooking because it is high in lauric acid, a fatty acid easily digested and absorbed by the body. Olive oil is good for cooking because of the heat-stable mono-saturated fats, plus it is packed with antioxidants and vitamin E, making it an excellent choice for the health conscious. With an overall neutral taste accented by faint, nutty tones, avocado oil is a good choice for cooking. It is milder than coconut and olive oil and, while it doesn't contain the fiber of the whole avocado fruit, it is still packed with health benefits. The healthy fats in avocado oil also help fight inflammation and protect the heart.
Fish oil, however, should never be used for cooking. Cooking breaks up the fragile poly-saturated fats and destroys many of the nutrients in fish oil. The same applies to flax oil, which has a similar composition to fish oil.