actually, there's a pretty easy answer to the fat question:

the only bad fat is hydrogenated fat (trans fatty acids). Sources of hydrogenated fat include margarine, commercial lard (real lard is great, but just try to find it!), every food in a box, frozen dinners, crackers, microwave popcorn, and regular commercial (soy) mayonnaise. Fats can also be damaged by overheating; most commercially available clear-looking vegetable oils are thus damaged (and then run through toxic chemicals as part of the filtering process).

Every other fat but hydrogenated is, in moderation, somewhere between fine for you and great for you. (Those fifteen words are a good-enough synopsis of the endless Erasmus book I've been reading--i just saved you the trouble!)

This is another reason (and there are dozens) to eat only real food that you've prepared yourself, and eat foods as close as possible to their natural state (raw nuts are better than roasted nuts are better than cold-pressed nut oils are much better than commercially processed clear vegetable oils). It's better to make your own mayo than buy it, and so on.

Scientists know some stuff...and Mother Nature knows a lot more.