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Evidence that palmitic acid is absorbed as sn ‐2 monoacylglycerol from human milk by breast‐fed infants
Author(s) -
Innis Sheila M.,
Dyer Roger,
Nelson Carolanne M.
Publication year - 1994
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02536625
Subject(s) - palmitic acid , monoacylglycerol lipase , fatty acid , lipase , breast milk , chemistry , hydrolysis , triglyceride , glyceride , milk fat , food science , biochemistry , cholesterol , enzyme , linseed oil , endocannabinoid system , receptor
Milk fatty acids consist of about 20–25% palmitic acid (16∶0), with about 70% of 16∶0 esterified to the sn ‐2 position of the milk triacylglycerols. Hydrolysis of dietary triacylglycerols by endogenous lipases produces sn ‐2 monoacylglycerols and free fatty acids, which are absorbed, reesterified, and then secreted into plasma. Unesterified 16∶0 is not well absorbed and readily forms soaps with calcium in the intestine. The positioning of 16∶0 at the sn ‐2 position of milk triacylglycerols could explain the high coefficient of absorption of milk fat. However, the milk lipase, bile salt‐stimulated lipase, has been suggested to complete the hydrolysis of milk fat to free fatty acids and glycerol. These studies determined whether 16∶0 is absorbed from human milk as sn ‐2 monopalmitin by comparison of the plasma triacylglycerol total and sn ‐2 position fatty acid composition between breast‐fed and formula‐fed term gestation infants. The human milk and formula had 21.0 and 22.3% of 16∶0, respectively, with 54.2 and 4.8% 16∶0 in the fatty acids esterified to the 2 position. The plasma triacylglycerol total fatty acids had 26.0±0.6 and 26.2±0.6% of 16∶0, and the sn ‐2 position fatty acids had 23.3±3.3 and 7.4±0.7% of 16∶0 in the three‐month‐old exclusively breast‐fed (n=17) and formula‐fed (n=18) infants, respectively. Marked differences were found in the plasma total and the 2 position phospholipid percentage of 20∶4ω6, i.e., 11.6±0.3 and 6.9±0.6 (total), 17.7±1.4 and 9.7±0.6 ( sn ‐2 position) and percentage of 22∶6ω3, 4.6±0.3 and 2.1±0.3 (total), 5.6±0.6 and 2.0±0.2 ( sn ‐2 position) for the breast‐fed and formula‐fed infants, respectively. These studies provide convincing evidence that 16∶0 is absorbed from human milk as sn ‐2 monoacyl‐glycerol. The metabolic significance of the differences in positional distribution of fatty acids in the plasma lipids of breast‐fed and formula‐fed infants is not known.