n−3 Fatty acid requirements of the newborn
Whether docosahexaenoic acid (22∶6n−3) is an essential nutrient for term or preterm infants, or if not, the quantity of dietary linolenic acid (18∶3n−3) needed to support sufficient synthesis of 22∶6n−3 for assimilation in the central nervous system is unknown. Infants fed formulas have lower plasma and red blood cell (RBC) levels of 22∶6n−3 than breast fed infants. No relationship between the intake of 18∶3n−3 in formula (0.8 or 4.5% of fatty acids, 18∶2n−6/18∶3n−3 ratio 35∶1 or 7∶1, respectively) and the infant's RBC 22∶6n−3 was found. Premature infants (<33 wk gestation) also showed a decrease in RBC 22∶6n−3 during feeding with formula containing 18∶3n−3 as the only n−3 fatty acid. However, a marked decrease in plasma and RBC 22∶6n−3 occurred between premature birth and the start of full enteral feeding at 1–2 wk of age. This was not reversed by breast milk or formula feeding. Piglets, which are appropriate for studies of infant lipid metabolism, had decreased brain synaptic plasma membrane, retina and liver 22∶6n−3 and increased 22∶5n−6 when fed formula with 0.8% fatty acids (0.3% of kcal) as 18∶3n−3. Formula with 4.0% fatty acids (1.7% of kcal) as 18∶3n−3 resulted in similar accretion of 22∶6n−3 in the organs compared to milk fed animals. The studies suggest the dietary requirement for 18∶3n−3 in term animals in energy balance exceeds 0.3% diet kcal. Studies in the premature infants suggest 18∶3n−3 may be oxidized rather than desaturated to 22∶6n−3 if energy requirements are not met, and that due to early lipid restriction and later rapid growth, premature infants may have higher dietary n−3 requirements than term infants.
central nervous system
long-chain polyunsaturated fatty acids of carbon chain ≥20 and containing >2 double bonds
low density lipoprotein
red blood cell(s)
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