Alpha-linolenic acid metabolism in men and women: nutritional and biological implications.
OBJECTIVE
This review critically evaluates current knowledge of alpha-linolenic acid metabolism in adult humans based on the findings of studies using stable isotope tracers and on increased dietary alpha-linolenic acid intake. The relative roles of alpha-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 alpha-linolenic acid. The extent of partitioning towards beta-oxidation and carbon recycling in humans is described. The use and limitations of stable isotope tracers to estimate alpha-linolenic acid desaturation and elongation are discussed. A consensus view of the extent of alpha-linolenic acid conversion to longer-chain fatty acids in humans is presented. The extent to which increasing dietary alpha-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.


RESULTS
Conversion of alpha-linolenic acid to eicosapentaenoic acid is limited in men and further transformation to docosahexaenoic acid is very low. A lower proportion of alpha-linolenic acid is used as a substrate for beta-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.


CONCLUSIONS
Overall, alpha-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 alpha-linolenic acid transformation in women may be important for meeting the demands of the fetus and neonate for docosahexaenoic acid.
Burdge
Graham
G
Institute of Human Nutrition, Biomedical Science Building, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, UK. g.c.burdge@soton.ac.uk
D002247:Carbon Isotopes; D015118:Eicosapentaenoic Acid / Q000378:metabolism; D004734:Energy Metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009751:Nutritional Requirements; D010084:Oxidation-Reduction; D012727:Sex Characteristics; D017962:alpha-Linolenic Acid / Q000008:administration & dosage / Q000378:metabolism* / Q000502:physiology
D002247:Carbon Isotopes; D005231:Fatty Acids, Unsaturated; D017962:alpha-Linolenic Acid; D015118:Eicosapentaenoic Acid; C026219:docosapentaenoic acid