Breast milk offers complete nutrition for the newborn baby and young infant. In addition, the maternal antibodies, chemical mediators, vitamins, enzymes and some types of white blood cells in breast milk (particularly in colostrum) augment the action of the baby’s immune system. At the height of lactation, the human breasts can produce up to 1.5 liters of milk (about 50 fluid ounces).
Milk is constantly being produced in the lactating breast. Initially when the baby suckles, little or no milk may be ejected from the nipple. This delay is a result of the suckling stimulating the secretion of oxytocin and prolactin. Oxytocin causes the myoepithelial layer of the lactiferous duct (explained under breast anatomy) to contract so that breast milk is pushed towards the nipple. Prolactin stimulates milk production. This is explained further under Breast Milk Production.
Types of Breast Milk
There are broadly three types of breast milk :
- Colostrum is a yellowish to cream colored substance that is high in protein but very low in fat compared to breast milk. It is also laden with immunological components and fat-soluble vitamins. It is present within the first few days after birth.
- Transitional milk is secreted during the latter stages of colostrum secretion and persist for between 10 days to 2 weeks until it is replaced by mature milk. It contains more fat and lactose than colostrum and has water-soluble vitamins.
- Mature milk is the type of milk will be present throughout lactation. The composition of mature milk is described below. Foremilk is first secreted when a baby starts to suckle and has a higher water content. It is then followed by hind-milk which is rich in carbohydrates, fats and protein.
Chemical Composition of Breast Milk
The composition of breast milk is as follows :
- Water : approximately 90%
- Carbohydrates (lactose) : approximately 6%
- Fat : approximately 3%
- Proteins (caesin, lactalbumins, etc) : approximately 1%
Other substances like the vitamins and minerals constitute less than 0.5% of breast milk. The composition of breast milk does vary slightly during lactation.
Human Milk vs Cow’s Milk
Human milk is ideally suited for babies. It contains key components that are required for proper growth and development as is required by the human body.
Human milk contains more water and significantly greater amounts of lactose than cow’s milk. There is little difference in the fat content of human and cow’s milk if the fats are considered in total rather than the different types of fats. Cow’s milk however, has significantly more protein than human milk. The vitamin and mineral content in cow’s milk is much higher than in human milk but certain vitamins and minerals that are necessary for human development may be lacking in cow’s milk.
Cow’s milk, however, is not suitable for infants. It lacks some of the key immunological components that are required by the human infant and the foreign proteins may trigger allergic reactions in some babies. Cow’s milk should be avoided in babies and breast milk can be replaced or supplemented by appropriate milk supplements developed for infants.