Digestion of Human Milk Fat in Early Infancy

Abstract

From an energetic point of view fat is the main nutrient during early infancy. Triglyceride (triacylglycerol) constitutes more than 95 % of the dietary fat and provides about half the energy in the diet of the milk fed infant. Each triglyceride molecule consists of three fatty acids esterified to one molecule of glycerol. Since greater than hundred individual fatty acids have been detected in human milk it is evident that not only the molecular structure but also the nutritional value may differ considerably between species of milk triglycerides (1). With this view in perspective it is noteworthy that current guidelines on infant nutrition give only few detailed recommendations on advisable amount and composition of fat in infant formulas for term an preterm infants. This reflects that available data in infants on qualitative and quantitative requirements of various lipid components are scanty.On the other hand it is reasonable to assume for lipids as well as other nutrients that the amount and composition of human milk is ideal to cover the needs of the newborn infant. Hence, current recommendations are based more on knowledge of the fat content and composition of human milk than on reliable data on requirements ( 2 ) . A drawback is however that even from formulas with a fatty acid composition very similar to human milk the coefficient of fat absorption is much lower than from raw milk, particularly in preterm infants. Moreover, calculated on individual fatty acids this difference in utilization is more pronounced for some fatty acid species than for others (3). From an increasing awareness that lipids serve other functions than being merely a source of exchangeable energy (4) it is obvious that future recommendations on fat composition of infant formulas must be based on more detailed data on requirements as well as on an understanding of the reasons behind the difference in utilization of fat from human milk compared to infant formulas. Before these reasons will be fully understood it is necessary to reveal the exact mechanisms of the digestion and absorption of milk triglyceride in the breast-fed infant.

The effect of storage at 25 °C on proteins in human milk

“…BSSL did undergo proteolysis during storage, with a 20% decrease in intensity seen after 4 h. Due to the importance of lipase for the digestion and absorption of triacylglycerols by the infant (Hernell, Blackberg, & Bernback, 1989), and its known sensitivity to milk storage and treatment procedures (Berkow et al, 1984;Czank, Simmer, & Hartmann, 2010), the lipase activity in the stored milk samples was also measured, to assess how it was affected by the observed proteolysis of BSSL. We found lipase activity to also be reduced by milk storage at 25 C, although to a greater extent than could be directly attributed to the proteolytic breakdown.…”

Serial composition of human milk in preterm and term mothers

“…to cover the needs of newborn infants (9). Triglycerides constitute more than 95% of the dietry fat and provide about half the energy in the diet of a milk fed infants.…”

Evidence that palmitic acid is absorbed assn‐2 monoacylglycerol from human milk by breast‐fed infants

“…The significance of sn-2 monoacylglycerol absorption in infants fed fresh human milk is, however, controversial because of the hypothesized role of the milk lipase, bile salt-stimulated lipase, in milk fat digestion. This enzyme is synthesized in the mammary gland, survives the acid environment of the stomach, and, at least in vitro, is able to complete the hydrolysis of milk triacylglycerols to form glycerol and free fatty acids (9)(10)(11)(12)(13). Additional hydrolysis of the products of endogenous lipase digestion of milk fat by bile salt-stimulated lipase has been suggested to explain the high efficiency of absorption of human milk (9)(10)(11)(12)(13).…”

“…This enzyme is synthesized in the mammary gland, survives the acid environment of the stomach, and, at least in vitro, is able to complete the hydrolysis of milk triacylglycerols to form glycerol and free fatty acids (9)(10)(11)(12)(13). Additional hydrolysis of the products of endogenous lipase digestion of milk fat by bile salt-stimulated lipase has been suggested to explain the high efficiency of absorption of human milk (9)(10)(11)(12)(13). Hydrolysis to release 16:0 from sn-2 monoacylglycerols formed by endogenous lipase activity, however, does not seem consistent with the specific positioning of 16:0 at the sn-2 position of human milk triacylglycerols, the low coefficient of absorption of unesterified 16:0, or the high coefficient of absorption of human milk fat in infants.…”