Interest in infant feeding has focused on energy, protein, essential fatty acids, and specific minerals. Biological advantages of feeding human milk versus proprietary formulas have been examined, with particular attention being accorded to the appropriateness of human milk for the premature infant and to the need to optimize the nutrient balance provided in semisynthetic formulations. The present paper will focus on the requirements for very long chain polyunsaturated essential fatty acids (Cz0 and CZ2), excluding considerations of fatty acid utilization for energy metabolism, to assess the basis of current knowledge concerning the infant's requirements for essential fatty acids.Metabolism of long chain polyunsaturated fatty acids derived from C18:zw6 and C I R :~~, )~ by chain elongation-desaturation ( Fig. 1) is essential for synthesis of complex structural lipids and prostaglandins. In homeothermic animals these essential fatty acids are required for normal function in developing tissues and appropriate maturation of a wide variety of physiological processes (reviewed by 1). During development, fetal accretion of long chain metabolites of 0 6 and 0 3 fatty acids may result from maternal or placental synthesis and transfer, or alternatively, the fetus may be capable of metabolizing C18:2w6 and CIS: 3,,,3 to longer chain homologues (2). After birth the infant must synthesize the very long chain polyunsaturated fatty acids (LCPE) derived from CI8, 2~6 and C18: 3w3 or be fed these fatty acids as they are normal constituents of most membranes.
Geometric and positional isomers of octadecanoic acid in milk expressed during the first 9 weeks of lactation were determined for mothers delivering prematurely (PT) and at term (FT). Total C18:1 concentration was lower in PT than FT milk. C18:1 trans (elaidic acid) content was higher in PT and FT colostrum compared with subsequent milk samples. No relationship was observed between C18:1 trans level in milk and oleic acid, linoleic acid, total fatty acid levels, or volume of milk expressed. While gestational age and lactational stage appeared to affect the trans fatty acid pattern, the overriding influence was rate of maternal postpartum weight loss. Effect of weight loss on milk trans fatty acid levels was independent of maternal diet. Trans fatty acid content of milk as a function of recent maternal fat intake was also demonstrated. This study indicates that infants receiving human milk ingest levels of trans fatty acids reflecting short and long term maternal diet.
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