I really enjoyed this article by Dr. Georgia Ede entitled, The Brain Needs Animal Fat.  It is a well written and easy to understand explanation that your brain is composed of by weight two thirds of some very specific kinds of fats.  Not only does it comport with evolution and natural selection, it is nice to see some push back on fat phobia that seems to be deep rooted in our nation.

Part of the problem is that the word fat has a dual meaning as in when a person is fat, or demonstrating adiposity, as we do when describing an entire macronutrient class.    She states:

Fat is not just for insulation and energy storage, it’s also for nutrient absorption, cell signaling, immune function, and many other critical processes. Many people think the main difference between plant and animal fats is that animal-sourced foods contain more saturated fat...

It's functions cannot be understated, lets look at some of them.  Yes a certain amount can provide insulation but that's not really important in humans as compared to some other animals.  Energy storage, yes.  This reminds us of cellular signaling.  Adipose tissue secretes a hormone called leptin.  It is also receptive to signals from insulin.  This means that fatty tissue is part of your endocrine system.  When they are in balance your body will store a correct amount of fat.  As for nutrient absorption, vitamins A, D, K, and E are the fat soluble.  No fat, no absorption no matter how much you consume.  It really is that simple

Most of what we term as non contagious chronic diseases (NCCD) or "Diseases of Civilization," have chronic inflammation as their underlying cause. A diet high in ALA mediate anti-inflammatory pathways.  A diet high in LA and carbohydrates will mediate inflammatory pathways.  Animal products does not necessarily mean red meat.  The correct nutrients can be found in seafood, including non-sentient clams, mussels, and oysters.

If you look at it from the prospective of evolution, we evolved from people who ate a nutrient dense animal based diet.  Yes they ate plants, too but they did not cook in high LA containing plant based oils or eat grain based products.  Nature knew what it was doing.  The right ratios of the right nutrients and fats have been there all along.  All we need is the wisdom to realize it.