METABOLISM OF LONG-CHAIN POLYUNSATURATED FATTY-ACIDS AND INFANT NUTRITION

There is increasing evidence that the premature infant may require a d ietary source of preformed 20 and 22 carbon long chain polyunsaturated fatty acids (LCPUFA). These LCPUFA, especially arachidonic acid (AA, 20 :4 n-6) and docosahexaenoic acid (DHA, 22:6 n-3), are necessary for proper growth and development and are consistently found in human mil k. Although born with the basic enzymic machinery, the premature infan t appears to be unable to synthesize sufficient AA and DHA from the sh orter is carbon chain precursors commonly available in vegetable fats. If the premature infant does not receive these preformed LCPUFA in th e diet, red blood cell and plasma phospholipid DHA levels decrease and AA shows a similar tendency. A study on the DHA content of brain of i nfants who died suddenly showed a lower level when the infants had bee n fed formula compared to breast milk. Differences in visual acuity an d intelligence quotient have also been demonstrated between breast fed and formula fed groups. For these reasons, the effects of adding LCPU FA to formula have been studied. Early experiments looked at formula s upplemented with fish oil since fish oil contains preformed DHA. When fed to premature infants, these formulae effectively increased DHA in red blood cell phospholipids. Visual acuity of the premature infant al so improved to a point where it was not detectably different from the breast fed group. However, growth was significantly depressed. This ma y be due to the presence in fish oil of eicosapentaenoic acid (EPA, 20 :5 n-3) which has structural similarities to AA. It is therefore impor tant to keep EPA levels as low as possible in infant formula. Arachido nic acid can be supplied to the infant directly as in egg lecithin, or indirectly as its precursor gamma-linolenic acid (GLA, 18:3 n-6). In infants, GLA feeding has been shown to increase AA levels in blood cho lesterol eaters. Egg lecithin is used to provide arachidonic acid but purification is desirable to eliminate traces of potentially allergeni c residual ovalbumin. In addition there may be variable levels of the AA and DHA content of the egg lecithin depending on the diet fed to th e chicken.