NCBI Bookshelf. Geneva: World Health Organization; Breast milk contains all the nutrients that an infant needs in the first 6 months of life, including fat, carbohydrates, proteins, vitamins, minerals and water 1234. It is easily digested and efficiently used. Breast milk also contains bioactive factors that augment the infant's immature immune system, providing protection against infection, and other factors that help digestion and absorption of nutrients. Breast milk contains about 3.
The fat is secreted in small droplets, and the amount increases as the feed progresses. As a result, the hindmilk secreted towards the end of a feed is rich in fat and looks creamy white, while the foremilk at the beginning of a feed contains less fat and looks somewhat bluish-grey in colour. Breast-milk fat contains long chain polyunsaturated fatty acids docosahexaenoic acid or DHA, and arachidonic acid or ARA that are not available in other milks.
These fatty acids are important for the neurological development of. DHA and ARA are added to some varieties of infant formula, but this does not confer any advantage over breast milk, and may not be as effective as those in breast milk. The main carbohydrate is the special milk sugar lactose, a disaccharide. Breast milk contains about 7 g lactose per ml, which is more than in most other milks, and is another important source of energy.
Another kind of carbohydrate present in breast milk is oligosaccharides, or sugar chains, which provide important protection against infection 4. Breast milk protein differs in both quantity and quality from animal milks, and it contains a balance of amino acids which makes it much more suitable for a baby.
The concentration of protein in breast milk 0. The much higher protein in animal milks can overload the infant's immature kidneys with waste nitrogen products. Breast milk contains less of the protein casein, and this casein in breast milk has a different molecular structure. It forms much softer, more easily-digested curds than that in other milks. Among the whey, or soluble proteins, human milk contains more alpha-lactalbumin; cow milk contains beta-lactoglobulin, which is absent from human milk and to which infants can become intolerant 4.
Breast milk normally contains sufficient vitamins for an infant, unless the mother herself is deficient 5. The exception is vitamin D. The infant needs exposure to sunlight to generate endogenous vitamin D — or, if this is not possible, a supplement. The minerals iron and zinc are present in relatively low concentration, but their bioavailability and absorption is high. Provided that maternal iron status is adequate, term infants are born with a store of iron to supply their needs; only infants born with low birth weight may need supplements before 6 months.
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Delaying clamping of the cord until pulsations have stopped approximately 3 minutes has been shown to improve infants' iron status during the first 6 months of life 67. Breast milk contains many factors that help to protect an infant against infection 8 including:. The protection provided by these factors is uniquely valuable for an infant. First, they protect without causing the effects of inflammation, such as fever, which can be dangerous for a young infant.
Second, sIgA contains antibodies formed in the mother's body against the bacteria in her gut, and against infections that she has encountered, so they protect against bacteria that are particularly likely to be in the baby's environment. Bile-salt stimulated lipase facilitates the complete digestion of fat once the milk has reached the small intestine 9. Fat in artificial milks is less completely digested 4. Epidermal growth factor 10 stimulates maturation of the lining of the infant's intestine, so that it is better able to digest and absorb nutrients, and is less easily infected or sensitised to foreign proteins.
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It has been suggested that other growth factors present in human milk target the development and maturation of nerves and retina Colostrum is the special milk that is secreted in the first 2—3 days after delivery. It is produced in small amounts, about 40—50 ml on the first day 12but is all that an infant normally needs at this time. Colostrum is rich in white cells and antibodies, especially sIgA, and it contains a larger percentage of protein, minerals and fat-soluble vitamins A, E and K than later milk 2.
Vitamin A is important for protection of the eye and for the integrity of epithelial surfaces, and often makes the colostrum yellowish in colour.
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Colostrum provides important immune protection to an infant when he or she is first exposed to the micro-organisms in the environment, and epidermal growth factor helps to prepare the lining of the gut to receive the nutrients in milk. It is important that infants receive colostrum, and not other feeds, at this time. Other feeds given before breastfeeding is established are called prelacteal feeds. On the third day, an infant is normally taking about — ml per 24 hours, and on the fifth day — ml From day 7 to 14, the milk is called transitionaland after 2 weeks it is called mature milk.
Animal milks are very different from breast milk in both the quantities of the various nutrients, and in their quality. For infants under 6 months of age, animal milks can be home-modified by the addition of water, sugar and micronutrients to make them usable as short-term replacements for breast milk in exceptionally difficult situations, but they can never be equivalent or have the same anti-infective properties as breast milk After 6 months, infants can receive boiled full cream milk Infant formula is usually made from industrially-modified cow milk or soy products.
During the manufacturing process the quantities of nutrients are adjusted to make them more comparable to breast milk. However, the qualitative differences in the fat and protein cannot be altered, and the absence of anti-infective and bio-active factors remain. Powdered infant formula is not a sterile product, and may be unsafe in other ways.
Infant and young child feeding: model chapter for textbooks for medical students and allied health professionals.
Life threatening infections in newborns have been traced to contamination with pathogenic bacteria, such as Enterobacter sakazakiifound in powdered formula Soy formula contains phyto-oestrogenswith activity similar to the human hormone oestrogen, which could potentially reduce fertility in boys and bring early puberty in girls The breast structure Figure 3 includes the nipple and areola, mammary tissue, supporting connective tissue and fat, blood and lymphatic vessels, and nerves 17 The mammary tissue — This tissue includes the alveoli, which are small sacs made of milk-secreting cells, and the ducts that carry the milk to the outside.
Between feeds, milk collects in the lumen of the alveoli and ducts. The alveoli are surrounded by a basket of myoepithelialor muscle cells, which contract and make the milk flow along the ducts. Nipple and areola — The nipple has an average of nine milk ducts passing to the outside, and also muscle fibres and nerves.
Anatomy of the female breast
The nipple is surrounded by the circular pigmented areolain which are located Montgomery's glands. These glands secrete an oily fluid that protects the skin of the nipple and areola during lactation, and produce the mother's individual scent that attracts her baby to the breast.
The ducts beneath the areola fill with milk and become wider during a feed, when the oxytocin reflex is active. There are two hormones that directly affect breastfeeding: prolactin and oxytocin. A of other hormones, such as oestrogen, are involved indirectly in lactation 2.
When a baby suckles at the breast, sensory impulses pass from the nipple to the brain. In response, the anterior lobe of the pituitary gland secretes prolactin and the posterior lobe secretes oxytocin. Prolactin is necessary for the secretion of milk by the cells of the alveoli. The level of prolactin in the blood increases markedly during pregnancy, and stimulates the growth and development of the mammary tissue, in preparation for the production of milk However, milk is not secreted then, because progesterone and oestrogen, the hormones of pregnancy, block this action of prolactin.
After delivery, levels of progesterone and oestrogen fall rapidly, prolactin is no longer blocked, and milk secretion begins. When a baby suckles, the level of prolactin in the blood increases, and stimulates production of milk by the alveoli Figure 4.
The prolactin level is highest about 30 minutes after the beginning of the feed, so its most important effect is to make milk for the next feed During the first few weeks, the more a baby suckles and stimulates the nipple, the more prolactin is produced, and the more milk is produced. This effect is particularly important at the time when lactation is becoming established.
Although prolactin is still necessary for milk production, after a few weeks there is not a close relationship between the amount of prolactin and the amount of milk produced. However, if the mother stops breastfeeding, milk secretion may stop too — then the milk will dry up.
More prolactin is produced at night, so breastfeeding at night is especially helpful for keeping up the milk supply. Prolactin seems to make a mother feel relaxed and sleepy, so she usually rests well even if she breastfeeds at night. Suckling affects the release of other pituitary hormones, including gonadotrophin releasing hormone GnRHfollicle stimulating hormone, and luteinising hormone, which in suppression of ovulation and menstruation.
Therefore, frequent breastfeeding can help to delay a new pregnancy see Session 8 on Mother's Health. Breastfeeding at night is important to ensure this effect.
Oxytocin makes the myoepithelial cells around the alveoli contract. This makes the milk, which has collected in the alveoli, flow along and fill the ducts 21 see Figure 5. Sometimes the milk is ejected in fine streams. Oxytocin is produced more quickly than prolactin.