Prostaglandins can be diveded into three series, depending on which fatty acid they derived from.
series-1 originates from gamma-linoleic acid
series-2 originates from arachidonic acid
series-3 originates from eicosapentaenoic acid
All of these compounds are present in different kinds of food and can be assumed with the diet.
The fatty acids absorbed are incorporated into the cell membrane and contribute to give it different chemical-physical properties.
Apart from the different physical properties, all of these fatty acids can be used by the cell to produce prostaglandins.
Since the three fatty acids previously listed differ by their structures, also the prostaglandins synthetized are different and, most important, their effect on the body is very diverse. Today, in a very simplistic view, it is usually possible to listen about "good" fat and "bad" fat. The "bad" fat is, in our case, arachidonic acid, while the "good" fats are linoleic acid and eicoesapentenoic acid (also commonly called, omega-3 fat). The distinction is based on the effect that the different kinds of prostaglandins have on the human body.
"Series 1" prostaglandins have three basic functions: they reduce inflammation, dilate blood vessels, and inhibit blood clotting.
"Series 2" strongly increase inflammation, constrict blood vessels, and encourage blood clotting.
"Series 3" could present a mix of effects: some of them dilate blood vessels, while others constrict. They also have a weak tendency to increase inflammation and inhibit blood clotting. In general, these are useful defense mechanisms against trauma and infection.
Anyway the important concept is that all of them are very important for the health of the body, but it is necessary that they are produced in the right equilibrium. This is possible only if a right diet is observed and a right ratio of different fatty acids is absorbed by the body.
A simple exemple of which types of food contain the fatty acid listed before, is displayed below:
Flax oil and some other vegetables oils are very rich in linoliec acid;
meat, eggs and butter are rich in arachidonic acid;
fish and fish oil are very rich of eicosapentaenoic acid (omega-3).
This is the reason why a diet very reach in meat consumption can favore a shift of the equilibrium toward an inflammation status, leading to develop, among the years, cardiovascular disease.
A different chapter can be opened about the fats chemically hydrogenated: some fatty acids are industrially treated to produce solid aliments (saturated or partially saturated) from liquid oil (poly insaturated). The hydrogenation process, if not completely terminated, can lead to the production of trans-insaturated fatty acid (the natural ones are cis-insaturated). These kinds of fatty acid are particularly dangerous for the health, because they block the the Delta-6 Desaturase and can not be catabolized by the cells, completely inhibiting the synthesis of "series-1" prostaglandins and reducing the synthesis of "series-3" prostaglandins (the D6D enzyme is essential for both series). Additionally, the modern diet is particularly rich in omega-6 fatty acid from soy, corn and cottonseed. Paradoxically an amount too high of this fatty acids could lead to the consumption of the Delta-6 Desaturase, favoring, also in this case, an impairment of the prostaglandins synthesis.
Which are the "good" and the "bad" prostaglandins and more exaustive informations can be found here