Essential fatty acids are fatty acids that are required in the human diet. This means they cannot be synthesized by the body from other fatty acids and must be obtained from food.
These fatty acids were originally designated as Vitamin F, until it was realized that they must be classified with the fats.
Linolenic acid, the shortest chain omega-3 fatty acid, and linoleic acid, the shortest chain omega-6 fatty acid, are essential fatty acids. The most common fatty acids of each class are linolenic (18:3), EPA (20:5), DHA (22:6) for omega-3 and linoleic (18:2) and arachidonic (20:4) for omega-6.
Essential fatty acids play a part in many metabolic processes, and there is evidence to suggest that low levels of essential fatty acids, or the wrong balance of types among the essential fatty acids, may be a factor in a number of illnesses.
Some text in this article was originally taken from the public domain resource at http://www.nal.usda.gov/fnic/foodcomp/Bulletins/faq.html#4-9-4