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This review critically evaluates current knowledge of α-linolenic acid metabolism in adult humans based on the findings of studies using stable isotope tracers and on increased dietary α-linolenic acid intake. The relative roles of α-linolenic acid and of longer-chain polyunsaturated fatty acids in cell structure and function are discussed together with an overview of the major metabolic fates of α-linolenic acid. The extent of partitioning towards β-oxidation and carbon recycling in humans is described. The use and limitations of stable isotope tracers to estimate α-linolenic acid desaturation and elongation are discussed. A consensus view of the extent of α-linolenic acid conversion to longer-chain fatty acids in humans is presented. The extent to which increasing dietary α-linolenic acid intake alters the concentrations of longer-chain n-3 fatty acids is described. The biological and nutritional implications of these findings are discussed.Conversion of α-linolenic acid to eicosapentaenoic acid is limited in men and further transformation to docosahexaenoic acid is very low. A lower proportion of α-linolenic acid is used as a substrate for β-oxidation in women compared with men, while the fractional conversion to longer-chain fatty acids is greater, possibly due to the regulatory effects of oestrogen.Overall, α-linolenic acid appears to be a limited source of longer-chain n-3 fatty acids in man and so adequate intakes of preformed n-3 polyunsaturated fatty acids, in particular docosahexaenoic acid, may be important for maintaining optimal tissue function. Capacity to upregulate α-linolenic acid transformation in women may be important for meeting the demands of the fetus and neonate for docosahexaenoic acid.