2008 by Taylor & Francis Group, LLC. The essentiality of fat in the diet has been known since 1929 (Burr and Burr, 1929, 1930), when it was rst recognized that linoleic acid (9,12-octadecadienoic acid, 18:2n-6), and possibly other acids, is an essential fatty acid (EFA). Since this initial observation, there have been numerous published studies documenting the fact that certain polyunsaturated fatty acids (PUFAs) cannot be synthesized de novo from endogenous precursors and are, therefore, essential dietary elements (Al n-Slater and Aftergood, 1968; Holman, 1971; Rivers and Frankel, 1981). Indeed, it is now recognized that there are two EFAs, 18:2n-6 and linolenic acid (9,12,15-octadecatrienoic acid, 18:3n-3). Although the volume of literature associated with the biological signi cance of PUFAs in laboratory animals is immense, relatively few studies have focused on the essentiality of 18:2n-6 and 18:3n-3 with respect to humans. In fact, the critical issues related to EFA physiological functions and requirements in humans are still being investigated. The results of some of these recent investigations are discussed in this review.
