Supplying energy is in fact the primary nutritional role of all edible oils and fats, though polyunsaturates tend to be spared this fate, because of their nutritional significance.
As a structural component
The presence of one or more double bonds means that the human body (and of course other animal species) can use these particular fatty acids to do things it can’t do with saturates. This is why the polyunsaturates, and to a lesser extent monounsaturates have an additional role or roles. Both these types of fatty acids also are used by the body to form an integral part of the structure of the membrane, or wall of the cells which go to make up the body itself. The properties of the cell membrane depend on the actual make up of fatty acids within it, and this is determined by several factors, including genetic make-up, but it is also influenced by diet. The way any particular cell responds to the various stimuli which may affect it from time to time will in part depend on the mixture of polyunsaturates and monounsaturates present in the membrane which makes up its wall. Such stimuli might be environmental, physiological, or indeed physical. The cell will only respond in the optimal manner if the membrane surrounding it is composed of the optimal mixture of fatty acids.To make powerful biological regulators
The third role for polyunsaturates is to be the raw material from which the body makes a range of intensely powerful, yet short-lived biological mediators. These influential chemical messengers control many different body processes, ranging from blood clotting, to digestion, from kidney function to the birth process itself. Both omega-6 and omega-3 polyunsaturates are needed for their structural properties, and as raw materials for the production of biological mediators. As a result of this, the polyunsaturates of the omega-6 and omega-3 families are known as the "essential fatty acids", or EFA's .Essential fatty acids
It is recognised that there are three "families" of polyunsaturates that are found in human nutrition, though the omega-9 family is of little significance nutritionally. The three families differ in the position of the first double bond counting from the methyl end (or the omega end), of the chain. These three families are known as the omega-3, omega-6 and omega-9 families (also known as the n-3, n-6 and n-9 families). The omega-9 family is only of significance when there is an insufficiency of either or both of the other two families, which are essential to human health, and must be supplied in the diet. When adequate amounts of omega-6 polyunsaturates and/or omega-3 polyunsaturates are not available, the body tries to compensate by producing omega-9 polyunsaturates to take the place of the essential omega-3 and/or omega-6 polyunsaturates. Though the omega-9 derivatives can substitute to a certain extent, they are not as effective as the omega-3 or omega-6 derivatives, and health will eventually suffer. The main value of the omega-9 polyunsaturates is as a marker for dietary insufficiency of the essential polyunsaturates.(published with permission in writing from:http://www.fish-foundation.org.uk/)
