Certain fatty-acids “are not produced” by the organism. They are called “essential fatty-acids”. As they are necessary to the constitution of the cellular membranes, sometimes it is necessary “to regulate” the food mode when they are in insufficient quantity.
See: Below, partial analyses of the composition of the fatty-acids in blood:
Saturated fatty-acids
Omega 3
Omega 6
Omega 9
A foundation of life maintenance system