Fats are made up of smaller compounds called fatty acids. Two of these are called essential fatty acids because they cannot be made by the body. The essential fatty acids are linoleic acid and alpha-linolenic acid. Linoleic acid is a member of a group of compounds called omega-6 fatty acids (the term refers to its chemical structure). It is found in vegetable oils and is usually abundant in North American diets.
Alpha-linolenic acid is a member of the group of omega-3 fatty acids. The body can change alpha linolenic acid into other omega-3 fatty acids called DHA and EPA. These are all important nutrients that play vital roles in growth, in the immune system, in proper eyesight, and in cell structure. Alpha linolenic acid is found in certain vegetable oils. DHA and EPA, in addition to being made by the body, are also found in some fatty fish such as salmon, mackerel, tuna, and sardines. Unlike omega-6 fatty acids, omega-3 acids are not usually abundant in North American diets, so it is important to be aware of foods that supply them.
[source: professional cooking sixth edition]