Ananda in Sanskrit means bliss, The compound Anandamide is present in chocolates and cocoa powder. It is structurally the ethanolamide of arachidonic acid. Biochemist Daniele Piomelli and coworkers isolated anandamide- from chocolate and cocoa powder. 

It is believed to bind to the same receptor site as tetahyddrocannabinol (THC)
Also Chocolates contain anandamide along with compounds that turn on the same receptor site in the brain as marijuana. This is believed to be responsible for the euphoria produced due to its consumpmtion. No wonder some people are addiced to chocolates.
C & En News- Sep 2, 1996.

Oils and fats are complex mixtures of many triglycerides. They are tri esters of glycerol(trihydroxy alcohol) and long chain carboxylic acids called fatty acids.
There are two types, saturated and unsaturated fatty acids ( have double bonds in their carbon chain). Unsaturated fatty acids with the double bonds and cis configuration are good for our health, while saturated/ trans are not.
Arachidonic acid is an unsaturated fatty acid has four double bonds. Walnut, fish are supposed to be rich in ω-unsaturated fatty acids, which are especially good for a healthy heart.