Essential Fatty Acid Requirements in Human Nutrition.
Essential Fatty Acid Requirements in Human Nutrition.
Year: 1993
Authors: S M Innis.
Publication Name: Can. J. Phys. Pharma.
Publication Details: Volume 71; 699.
Abstract:
The author has published several studies on the dietary PUFA requirements of term and preterm infants. In this review article she describes the importance of dietary intakes of LA and ALA on tissue and cell membrane levels of AA and DHA and provides an extensive overview of the metabolism of EFAs. These long chain PUFAs are integral fatty acids in cell membrane phospholipids, and are found in high levels in the nonmyelin membranes of the central nervous system. She reviews numerous studies in which assessments of the EFA requirements for optimal growth and development have been undertaken. This research has shown that deficiencies in dietary LA and ALA during infant development results in reduced levels of AA and DHA in the developing central nervous system. These findings have been associated with altered learning behaviour and visual function. In this paper, Innis reviews several studies that have shown that the synthesis of AA and DHA depends on the dietary intake of LA and ALA, respectively. In addition, AA and DHA synthesis is also influenced by the activities of the desaturase and elongase enzymes responsible for their conversion from LA and ALA. Oxidation of LA and ALA for energy, or direct acylation of LA into TGs, cholesteryl esters, and phospholipids, may also influence the amount of AA and DHA formed. Research has not yet established the tissue levels of AA and DHA, or other n-6 and n-3 fatty acids, compatible with optimum growth and development or overall health. Innis indicates that the circulating lipid levels of DHA has been correlated to the amount of performed DHA in the diet of adults, in infants fed various milks or formulae, and in animals. However, she believes that dietary requirements for n-6 and n-3 fatty acids in humans should be based upon direct measures of functions known to relate to central nervous system or other organ levels of the FA in question, rather than diet-related differences in blood lipid FAs. Human milk levels of n-6 and n-3 fatty acids vary, depending in part on the mother’s diet and will impact on tissue levels of AA and DHA. However, Innis stresses that a valid, scientific approach to extrapolate the requirements of dietary EFAs from the composition of human milk or the circulating lipids of infants fed different diets is an area of controversy. Innis indicates that current research suggests that fatty acid requirements for development of term-gestation piglet brain and retina are met with 5.0% of dietary kcal as LA and >1.0% kcal as ALA. The same type of data is not available for humans. Although not supported by all researchers in this area, Innis states that, in rodents and non-human primates, a dietary source of AA and DHA does not appear essential for developing piglet central nervous system. In contrast, data from studies assessing the PUFA requirements of very premature infants (< 33 weeks gestation) suggests that a dietary source of AA and DHA may be important. In this infant population, it has not been established whether the low AA and DHA status noted is due to oxidation of LA and ALA to meet energy needs. Alternatively, Innis presents the hypothesis that low AA and DHA levels in very preterm infants may also be due to the effects of early intravenous feeding with lipid emulsions, rapid growth, or immaturity of physiological or metabolic pathways. Further research in these areas is on-going.
