Metabolism and function of alpha-linolenic acid in humans. In: Flaxseed in Human Nutrition.
Metabolism and function of alpha-linolenic acid in humans. In: Flaxseed in Human Nutrition.
Year: 1995
Authors: S C Cunnane.
Publication Name: AOCS Press, Champaign, Ill.
Publication Details: ;99;127.
Abstract:
This book chapter provides an extensive overview of the metabolism and physiological functions of ALA in humans. The author notes that is has been difficult to ascribe a specific nutritional role for ALA, aside from being a precursor to EPA and DHA, so it has been difficult to demonstrate clinical attributes of ALA that are independent of EPA or DHA. In this chapter, the conversion of ALA to EPA and DHA and its influence on eicosanoid metabolism is described. The author indicates that the average dietary intake of ALA in North America has been estimated to be about 1 g/day or 0.5% of energy intake. Since the most common sources of ALA in the diet, soybean and canola oils, are often hydrogenated, the ALA content of Western style diets will be reduced. Cunnane reports that dietary supplementation of ALA in the form of flaxseed oil results in significant conversion of ALA to EPA and DHA within platelet cells. Eleven human studies in which levels of ALA of between 1 and 40 g/day were fed for periods ranging from 2 weeks to 6 months in duration are reviewed in this chapter. ALA, EPA and DHA levels in blood plasma or serum lipid fractions increased with increasing levels and duration of flaxseed oil supplementation. These findings indicate that ALA can serve as a source of EPA in the body and therefore, can supply the precursor of the series 3 and 5 eicosanoids. Cunnane indicates, however, that the efficiency of ALA conversion to EPA and DHA is species dependent; is more effective during dietary deficiency of EPA and DHA and will be influenced significantly by competition with the n-6 PUFAs. The importance of ?-oxidation of ALA and how it varies with total fat and energy intake are discussed. The contribution of ALA to energy metabolism and the recycling of ALA carbon skeletons are reviewed. The function of ALA in humans is described. Recent clinical studies suggest that dietary ALA can reduce the risk of mortality from a number of diseases, most notably, cardiovascular disease and cancer. Cunnane reviews studies that are discussed in greater detail in other sections of this Bibliography. The role of ALA in early human development and learning is described with particular emphasis on the importance of ALA as an essential nutrient to supply DHA for normal neonatal brain and retinal development. The author provides an overview of his research on the nutritional effects of flaxseed and flaxseed oil in humans. Cunnane concludes by stating that it is becoming clear that ALA has an important, but as yet not well-defined, protective role against degenerative Western diseases. The essentiality of ALA in the diets of infants and adults is well established.
