Abstract
Human milk lipids are essential for infant health. However, little is known about the relationship between total milk fatty acid (FA) composition and polar lipid species composition. Therefore, we aimed to characterize the relationship between the FA and polar lipid species composition in human milk, with a focus on differences between milk with higher or lower milk fat content. From the Norwegian Human Milk Study (HUMIS, 2002–2009), a subset of 664 milk samples were analyzed for FA and polar lipid composition. Milk samples did not differ in major FA, phosphatidylcholine, or sphingomyelin species percentages between the highest and lowest quartiles of total FA concentration. However, milk in the highest FA quartile had a lower phospholipid-to-total-FA ratio and a lower sphingomyelin-to-phosphatidylcholine ratio than the lowest quartile. The only FAs associated with total phosphatidylcholine or sphingomyelin were behenic and tridecanoic acids, respectively. Milk FA and phosphatidylcholine and sphingomyelin species containing these FAs showed modest correlations. Associations of arachidonic and docosahexaenoic acids with percentages of phosphatidylcholine species carrying these FAs support the conclusion that the availability of these FAs limits the synthesis of phospholipid species containing them.
Highlights
Human milk is the optimal source of infant nutrition during the first 4–6 months of life, and provides nutrients, bioactive compounds, and immunological factors to support healthy growth and development [1,2,3,4].Fat contributes around half of the energy intake of breastfed infants, and provides indispensable polyunsaturated fatty acids (PUFAs) and lipid-soluble vitamins [2,5]; it is the most variable macronutrient in human milk, with content ranging from 2.4 to 5.5 g/100 mL (10th to 90th percentiles) [6]
Lipids are emulsified as milk fat globules (MFGs) that consist of a triacylglycerol (TAG)-rich core surrounded by a tri-layered milk fat globule membrane (MFGM) comprising glycerophospholipids, sphingolipids, cholesterol, and proteins [5,7,8]
We aimed to investigate whether FA and polar lipid composition in human milk differs between milk samples with high and low-fat content, and whether milk total FA composition is associated with the milk polar lipid species phosphatidylcholine (PC) and SM
Summary
Human milk is the optimal source of infant nutrition during the first 4–6 months of life, and provides nutrients, bioactive compounds, and immunological factors to support healthy growth and development [1,2,3,4].Fat contributes around half of the energy intake of breastfed infants, and provides indispensable polyunsaturated fatty acids (PUFAs) and lipid-soluble vitamins [2,5]; it is the most variable macronutrient in human milk, with content ranging from 2.4 to 5.5 g/100 mL (10th to 90th percentiles) [6]. Lipids are emulsified as milk fat globules (MFGs) that consist of a triacylglycerol (TAG)-rich core surrounded by a tri-layered milk fat globule membrane (MFGM) comprising glycerophospholipids, sphingolipids, cholesterol, and proteins [5,7,8]. The importance of milk LCPUFAs—including n-6 arachidonic acid (ARA) and n-3 docosahexaenoic acid (DHA)—for infant development has been recognized [9], but only recently has the importance of the complex polar lipids in the MFGM for infants’ gut maturation and the establishment of the intestinal immune system been described [10]. Positive effects of MFGM supplementation on infants’ cognitive development and infection risks suggest that individual components of MFGM (e.g., choline, sphingomyelin, gangliosides, and cholesterol) may play important roles in the neurodevelopment and immune system maturation of infants [11]. The binding of phosphocholine forms sphingomyelin (SM)—a major polar lipid component in both cell membranes and MFGMs [17,18]
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