Human milk fat is well absorbed despite its large concentration of long-chain saturated fatty acids (LCSFA), particularly palmitic acid. The superior absorption has been ascribed in part to the uncommonly high proportion of the palmitic acid in the sn-2 position of the triglycerides, 70% in human milk triglycerides compared with 10-15% in the fats and oils commonly used in infant formula blends. Colipase-dependent pancreatic lipase selectively hydrolyzes the fatty acids at the sn-1 and 3 positions, yielding free fatty acids and the 2-monoglyceride, which are absorbable. Free palmitic acid, but not monopalmitin, can be lost as calcium soaps in the feces. The present study demonstrated that mixtures of coconut oil and palm olein are better absorbed by rats if the proportion of LCSFA in the sn-2 position is increased by the process of chemical randomization, in which the fatty acids of the native oils are redistributed equally to all three positions in the rearranged triglycerides. The fecal excretion of total fatty acids, essentially LCSFA, from the mixtures in which the oils were randomized together (corandomized) was 30 to 60% less than from the mixtures of native oils.

Rapidly growing neonatal mammals accrete relatively large quantities of long chain (> or = C20) polyunsaturated fatty acids (LCP) in membrane phospholipids. We have examined accumulation of omega 6 LCP in suckling neonatal rat pups during the first 14 d of life when their dams received essential fatty acids in the form of triglycerides containing linoleic acid or arachidonic acid. Dietary levels of these fatty acids were either 1 or 5% of total dietary fatty acids. The fatty acid profile of pup stomach contents (composed solely of the dams' milk) and plasma lipids, as well as liver and brain phospholipids, were determined. Stomach linoleic and arachidonic acid levels reflected the diet of the dams. Pup plasma and liver arachidonic acid levels increased progressively from the group receiving 1% linoleic acid to 5% linoleic acid and from 1% arachidonic acid to 5% arachidonic acid. Interestingly, brain phosphatidylethanolamine and phosphatidylcholine arachidonic acid levels were more stable than plasma or liver levels. These results suggest that the brain may be capable of either selective transport of omega 6 LCP or chain elongation/desaturation of linoleic acid. These data indicate that care must be exercised when adding LCP to infant formula since widely divergent accretion rates of arachidonic acid may occur in various tissues.