We have a sticky on fat but it's a little out of date: viewtopic.php?f=17&t=4137
Since then we've learned more about fat. It seems that most of the negatives associated with fats have to do with oxidization, or rancidity. Oxidization causes free radicals which cause cancer. Different types of fats have an operating range of temperatures that they're stable at. The plants and animals that contain the fats need them to be liquid at their operating temperatures but not prone to oxidization. that's why animals and tropical plants have fat that's hard at room temperature but liquid at body temperature. Similarly, cold water fish have fats that are liquid at low temperatures. Your body needs mostly the hard fats since these are least prone to oxidization.
The types of fats to be most wary of are fats that require heat in order to extract them. Oils from seeds, for example, need to heated and treated with chemicals in order to be used. This heat, causes oxidization of the delicate polyunsaturated fats they contain. On the other hand, olive oil is cold extracted. The mono-unsaturated fats they contain are also more stable since olives grow in a warmer climate. Most stable are the tropical oils found in coconuts and palms as well as warm blooded animals. These also don't require heat for extraction. These are also the most stable. This is why margarine has to be kept in the fridge but butter, olive and coconut oil can be kept out.
Saturated and mono-unsaturated fats can be consumed in any amount but you want to restrict your poly unsaturated fats to the essential amount required by the body. This is actually a very small amount, about 3-4% of calories in total. About half should be omega 3 and half omega 6. Your total fat intake needs to be at least 30% but can be as high as 80% of your calories.
Fats are your body's preferred source of energy.
Artificial fats of any type are unhealthy.