THE ROLE OF FATTY-ACID COMPOSITION AND POSITIONAL DISTRIBUTION IN FAT-ABSORPTION IN INFANTS

Fat digestion and absorption in the infant is a multistep process. An initial gastric phase of lipolysis generates modest amounts of diglyce rides, monoglycerides, and free fatty acids. These initial digestion p roducts, as well as bile salts, are required for optimal activity of t he intestinal phase of lipolysis. Colipase-dependent pancreatic lipase catalyzes the intraduodenal phase of triglyceride digestion in formul a-fed infants; in breast-fed infants this process is also mediated by bile salt-stimulated lipase. Triglyceride fatty acid positional distri bution may modulate the efficiency of nutrient absorption. Human milk contains palmitic acid (C16:0) primarily in the sn-2 position; infant formula fat blends contain palmitic acid predominantly in the sn-1 and sn-3 positions. Because pancreatic lipase selectively hydrolyzes trig lycerides at the sn-1 and sn-3 positions, free fatty acids and 2-monog lycerides are produced. Flee palmitic acid, but not 2-monopalmitin (wh ich is efficiently absorbed), may be lost as a calcium-fatty acid soap in the feces. As a result, many infant formulas contain substantial l evels of well-absorbed saturated fatty acids of shorter chain lengths (e.g., C12:0) in place of palmitic acid. Means of increasing the propo rtion of 2-palmitic acid in infant formula may make possible fat blend s closer to that of human milk with acceptable absorption characterist ics.