Focus Module - The Milk Fat Globule and its Membrane
Human milk fat is a major source of energy for the breastfed infant. It also provides infants with essential nutrients and bioactive components that support health and development.
In human milk, fat is present in the form of so called Milk Fat Globules (MFG). Components from the milk fat globule membrane, such as proteins, polar lipids and cholesterol, have been linked to potential benefits for the infant’s health. In this module, you will learn about the latest scientific evidence on human milk fats and their positive effects on gastrointestinal and metabolic health, and other health outcomes such as immunity and neurodevelopment.
An overview of the complex composition of the MFG is presented, including the physiological effects of its bioactive molecules. Moreover, this module will introduce you to recent findings exploring the potential benefits of supplementing breast milk substitutes with MFGs from bovine origin.
Unit 1: Human Milk Fat. Composition and Health Effects
In human milk, fat is present in the form of milk fat globules (MFG). These are composed of a core rich in non-polar lipids, and a tri-layer membrane, which is mainly composed of polar lipids. The predominant components of human milk fat are the triacylglycerides present in the core. However, the molecules present in the membrane, such as phospholipids, cholesterol and membrane proteins have shown to have important bioactivities. The milk fat globule membrane (MFGM) is therefore the main functional part, providing components from the breast epithelial cells of the mother.
Besides the often more than twofold increase of milk fat content from foremilk to hind milk, the fat content is variable and influenced by multiple factors, including maternal dietary intake, mother´s genotype, and gestational length, weight gain during pregnancy, breast fullness and stage of lactation. These differences have been proposed to reflect adaptation of human milk composition to the infant’s changing needs. For instance, the hungrier infants are, the more milk they will suckle, and therefore the emptier the breast will be. Milk from emptier breasts has a higher fat concentration than milk from full breasts, this allows providing a higher caloric intake to hungrier children who suckle longer trying to get a higher energy consumption. Human milk is the ideal nutrition for infants and appropriate dietary recommendations for the mother can help to ensure the nutritional quality of human milk.
The specific composition of human milk fat, and the presence of bioactive components has been associated to benefits in health outcomes, including benefits due to improved nutrient absorption, long-term metabolic health and protection against pathogen invasion. Human milk contains bile-salt-stimulated lipase (BSSL), which enhances fat breakdown. In addition, in the milk fat globule core, triacylglycerides have a specific distribution of fatty acids (palmitic acid in sn-2 position), which has been suggested to improve palmitic acid and calcium absorption in the infant´s intestine. Human milk fat is rich in cholesterol, which has been suggested to enhance downregulation of cholesterol synthesis in infants, and therefore lowering serum LDL cholesterol in adult life. The outer layer of the MFGM includes proteins and glycolipids which can act as decoy receptors for pathogens, so that they are bound and expulsed through stool, protecting the infant´s intestinal epithelium form invasion.
Human milk fat globules are composed of bioactive molecules, which act in complex interactions providing benefits for infant health and development.
Unit 2 - Addition of Fractionated Dairy Lipids to Breast Milk Substitutes
In breast milk substitutes (BMS), bovine fat is often removed and replaced by vegetable oil blends. This practice improves the provision of the essential fatty acids linoleic acid (LA) and alpha-linolenic acid (ALA) whose content in bovine milk is insufficient. Hypothesis based on preclinical studies, suggest that absorption of calcium and palmitic acid may be reduced due to the low proportion of palmitic acid in sn-2 position in vegetable fat triacylglycerides. Moreover, vegetable fat lacks the bioactive components of the MFGM, suggesting that health outcomes in neurodevelopment, immunity and metabolic health may be different. This may in part explain the advantageous health outcomes of human milk fed infants compared to infants fed vegetable oil based BMS
In order to reduce the gap between the health outcomes observed in breastfed infants, and those fed BMS, recent studies investigate the potential benefits of supplementing BMS with dairy fat including MFGM of bovine origin. Preclinical data has shown promising results, reporting some associations between MFGM components and health benefits in vitro and in animals.
Although evidence regarding the effects of supplementing BMS with dairy MFGM in infants is limited, recent research from randomized controlled trials (RCT) suggests that inclusion of MFGM into infant feeding is safe. There are signs of benefits regarding infant´s immunity, neurodevelopment and gastrointestinal and metabolic health; however, findings are often not consistent with those of preclinical studies.
Further research is needed in order to identify the potential long-term health benefits of supplementing BMS with dairy lipid fractions, and to explore the best composition of MFGM preparations for inclusion in BMS.