Nutrient Composition of Human Milk
Section snippets
ASSESSING INFANT NUTRITIONAL REQUIREMENTS
Intakes of thriving breastfed infants often serve as the standard for infant nutrition, but other approaches for the assessment of infant nutritional requirements exist, including direct experimentation, metabolic balance studies, clinical observations of deficiencies, and theoretically based calculations.13 The latter approaches provide information that is useful for the formulation of human milk substitutes and for assessing whether maternal nutritional inadequacy is evident and when
MATERNAL NUTRITION
The nutritional requirements to support lactation are among the highest in human development. The production of 750 to 1000 mL/d of human milk represents 2100 to 2520 kJ/d transferred as energy-yielding macronutrients to nursing infants. Also, all vitamins and minerals required to support growth and development of growing infants are likewise transferred. Nutritional needs to support lactation are exceedingly high and often not fully appreciated. The estimated energy cost of 6 and 9 months of
COMPOSITION OF HUMAN MILK
Human milk is a complex biological fluid composed of thousands of constituents in several compartments: an aqueous phase with true solutions (87%), colloidal dispersions of casein molecules (0.3%), emulsions of fat globules (4%), fat-globule membranes, and live cells. Human-milk constituents can be broadly categorized according to their physical or physiologic properties. These categories of constituents include:
Proteins
α-Lactalbumin
β-Lactoglobulin
Caseins
Enzymes
Growth factors
Protein and Nonprotein Nitrogen
Human milk protein content [(total nitrogen − nonprotein nitrogen) × 6.25] is high in early secretions, 15.8 g/L, and slowly decreases to 8.0 to 9.0 g/L with the establishment of lactation.12, 27 The protein constituents of human milk serve diverse functions. Besides providing essential amino acids for growth, they provide protective factors (e.g., immunoglobulins, lysozymes, and lactoferrin), carriers for vitamins (e.g., folate, vitamin D, and vitamin B12 binding proteins), and for hormones
SUMMARY
A complex interplay of maternal homeostatic mechanisms influences nutrient transfer to nursing infants, and with a few exceptions, excess maternal intake or a moderate deficiency in the maternal diet does not appreciably alter nutrient transfer to infants unless it has persisted for some time. Milk vitamins D and K contents, even in apparently well-nourished women, may not always provide adequate amounts for infants. Investigations provide evidence that human milk possesses many unique
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Address reprint requests to Mary Frances Picciano, PhD Department of Nutrition The Pennsylvania State University 126 Henderson Building South University Park, PA 16802 e-mail: [email protected]
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Department of Nutrition, The Pennsylvania State University, University Park, Pennsylvania