Interaction of n-3 long-chain polyunsaturated fatty acids with n-6 fatty acids in suckled rat pups

The addition of long-chain polyunsaturated fatty acids (LCP: C20, and C22) to infant formula may permit fatty acid accretion rates similar to breast-fed infants, and may have long-term outcome benefits, such as improved visual acuity and cognitive development. Although fish oil may provide a source of n-3 LCP, sources of n-6 LCP have been more difficult to identify. The present study evaluates the effects of n-3 and n-6 LCP derived from single-cell oils on liver, plasma, and brain fatty acid levels in a neonatal animal model. Newborn rat pups were suckled for 14 d by dams receiving diets containing n-3 LCP alone or combinations of n-3 LCP and increasing doses of linoleic acid (18:2n-6) or arachidonic acid (20:4n-6). Dietary groups received 2% n-3 LCP and 1, 2, or 5% of either 18:2n-6 or 20:4n-6. The 20:4n-6 source also contained modest levels of 18:2n-6. At the termination of the study, liver, plasma, and brain were obtained from the rat pups and the phospholipid fatty acid profiles determined. The results indicate complex interactions of n-3 and n-6 fatty acids. Groups receiving dietary 20:4n-6 incorporated higher levels of n-6 LCP into tissues than did the groups receiving 18:2n-6. The brain was relatively resistant to changes in fatty acid composition compared with the liver and plasma. As expected, tissue n-3 LCP levels were reciprocally related to n-6 levels. The present results document that single-cell LCP oils are bioavailable in a neonatal animal model. The use of 20:4n-6 is a more effective means of supporting n-6 status than the use of 18:2n-6. These results may have implications for the addition of LCP to infant formula.