I know the whole low-fat thing was bogus to begin with, but besides needing fat to absord fat soluble vitamins, like A and D, can someone give me a list of why it's not only ok to eat fat, but necessary? Thanks!
Because your body evolved to use fat as its principal and prefered energy supply?
Your body has a limited capacity to utilize and store carbohydrate (as glycogen), if you exceed that one of the disposal pathways is to convert excess glucose into fat (de-novo-lipogenesis). It's much better to eat fat, than eating lots of carbohydrates to turn into fat.
You can feed your body from your fat stores for weeks, or even months, but ultimately you'll exhaust them.
There are certain fatty acids that our bodies cannot make and are required for life. In other words if you do not eat them you will eventually get sick and die. The low fat people sometimes call these "good fats." In addition fats provide energy and aid in the absorption of some minerals and micro-nutrients.
Normal resting metabolism energy spent is about 2/3 beta oxidation of fatty acids and 1/3 oxidation of glucose. Your body requires a fair amount of fat for energy. And your body requires fat for structure such as the bi-lipid layer of your cell membranes. So fat is required. Do you need to eat it? If you are lean, I think the answer is yes. If you are obese, you probably need to eat some (for vitamins and such), but you could probably eat much less and supply the requirement from your fat cells.
Bile is stored in the gallbladder and is released when a meal with a decent amount of fat in it is eaten. If you don't eat any fat for a long time the bile will stagnate and form gallstones which can block the gallbladder and cause other problems.
If you have enough fat to provide energy to run your optimal body AND absorb the necessary nutrients, you don't need more. The problem is that most people seem to be deficient.
While I love the taste of fat, I think some of the ultra high fat protocols are over the top unless there is a specific medical condition being addressed with it.
bottom line, fat is used to create hormones in the body. you can be "low-fat" and still be healthy, as long as the fat you are getting is saturated and enough to manufacture the hormones. you don't need to be ketogenic or eat gobs of fat to fuel yourself. just figure out how much fat you specifically need to create your hormones, have good skin and collagen, and be satiated with meals. no need to overdo fat for some paleo mythology.