Human Breast Milk

Human Breast Milk: Nutritional Composition and Importance

Human breast milk is the natural food source for human infants, produced by the mammary glands of the mother following childbirth. This entry is a nutritional reference rather than a consumer food guide. Breast milk has been the subject of extensive scientific research given its critical importance for infant health and development — it is the biological template against which all infant formula products are measured and compared. The composition of breast milk changes dramatically over the course of lactation: colostrum, produced in the first few days, is dense with immune factors, antibodies, white blood cells, and growth factors despite being low in volume; transitional milk follows over the first few weeks; mature milk, which continues throughout breastfeeding, provides the nutritional composition recorded in this entry. Even within a single feeding, the composition changes — foremilk at the start is lower in fat, hindmilk at the end is higher in fat and caloric density.

Nutritional Composition of Human Breast Milk

Mature human breast milk provides approximately 70 kcal and 1 g of protein per 100 ml, with 4.4 g of fat. While the protein content is lower than cow's milk, it is specifically formulated for human infant needs — the protein is predominantly whey proteins (alpha-lactalbumin, lactoferrin) that are easily digested by infants and carry additional biological functions beyond nutrition. The fat is rich in long-chain polyunsaturated fatty acids, particularly DHA (docosahexaenoic acid) and arachidonic acid (ARA), which are critical for brain and retinal development. The primary sugar is lactose, providing energy and supporting the growth of beneficial gut bacteria.

Immunological and Bioactive Components

Beyond its nutritional composition, breast milk contains an extraordinary range of bioactive components: immunoglobulins (particularly secretory IgA) that provide passive immune protection; lactoferrin, which has antimicrobial and anti-inflammatory properties; lysozyme, which attacks bacterial cell walls; human milk oligosaccharides (HMOs) that selectively feed beneficial gut bacteria; stem cells; hormones including leptin and adiponectin; and growth factors. These components cannot be fully replicated in infant formula and represent a biological system of considerable complexity. The WHO and UK health authorities recommend exclusive breastfeeding for the first six months of life, with continued breastfeeding alongside solid foods thereafter.

Health Significance of Breastfeeding

The research evidence on breastfeeding is substantial and consistent: breastfed infants show reduced rates of respiratory tract infections, gastrointestinal illness, otitis media (ear infections), sudden infant death syndrome (SIDS), and childhood obesity compared to formula-fed infants. Long-term associations with reduced risk of type 2 diabetes, certain cancers, and cardiovascular disease have also been reported. Breastfeeding also confers health benefits on mothers, including reduced risk of breast cancer, ovarian cancer, and type 2 diabetes. The composition of breast milk is influenced by maternal diet, with nutrients including DHA, iodine, vitamin D, and vitamin B12 varying based on maternal intake.