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Abstract
Fat digestion and absorption in the infant is a multistep process. An initial gastric
phase of lipolysis generates modest amounts of diglycerides, monoglycerides, and free
fatty acids. These initial digestion products, as well as bile salts, are required
for optimal activity of the intestinal phase of lipolysis. Colipase-dependent pancreatic
lipase catalyzes the intraduodenal phase of triglyceride digestion in formula-fed
infants; in breast-fed infants this process is also mediated by bile salt-stimulated
lipase. Triglyceride fatty acid positional distribution 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 triglycerides
at the sn-1 and sn-3 positions, free fatty acids and 2-monoglycerides are produced.
Free palmitic acid, but not 2-monopalmitin (which is efficiently absorbed), may be
lost as a calcium-fatty acid soap in the feces. As a result, many infant formulas
contain substantial levels of well-absorbed saturated fatty acids of shorter chain
lengths (e.g., C12:0) in place of palmitic acid. Means of increasing the proportion
of 2-palmitic acid in infant formula may make possible fat blends closer to that of
human milk with acceptable absorption characteristics.