Breast milk: composition and functions

Breast milk is the natural liquid food produced by all mammals for feeding a newborn. The milk is considered a rich and irreplaceable source of nutrition for babies who begin their growth but more importantly, while feeding the baby, a very positive bond between mother and baby appears.

How is breastmilk produced?

The hormones prolactin and oxytocin are responsible for stimulating milk production. Prolactin is the one that produces milk, and oxytocin causes the milk’s escape through the nipple.

The stages of breast milk

(The properties and composition of breast milk varies depending on the stage)

Precolostrum: During the third trimester of pregnancy, the breasts tend to secrete a fluid composed of plasma, sodium, chlorine, immunoglobulins, lactoferrin, serum albumin and some lactose. This fluid is called precolostrum and warns that the breasts are preparing to nurse the new baby.

Colostrum: This is a liquid secreted by the breasts the first few days right after childbirth. It is a thick and yellowish fluid which is due to the high percentage of beta carotene (precursor of vitamin A). This kind of milk is ideal as baby's first food because it will help the child to strengthen their defenses and immune system will adapt to new conditions of life as colostrum contains high amount of defense factors such as immunoglobulin A, lactoferrin, lymphocytes, macrophages, etc., all these favor the baby's immune mechanism, preventing adhesion of pathogenic microorganisms in the digestive tract and facilitating the colonization of Lactobacillus bifidus.

The amount of colostrum is secreted may vary between 2 to 20 ml per dose in the first 3 days, enough to meet the nutritional demands of the newborn. This fluid provides about 67 Kcal per 100 ml, and is richer in protein, vitamins A, E, K, sialic acid, good fats and some minerals (sodium, iron, zinc, sulfur, potassium, manganese, selenium) compared with mature milk. Furthermore, colostrum contains high percentage of enzymes, which help the digestive system facilitating the assimilation and disposal, which helps prevent yellowing of the skin of the newborn (jaundice).

Transitional milk: after colostrums, women produce what is called transitional milk, which begins to secrete from the fourth postpartum day and lasts about ten days. In this milk there is a gradual increase between 600 – 700 ml per day, but may vary according to the mother.

Mature milk: the milk that follows the transition milk which is secreted on average about 700-900 ml / day for 6 or 7 months and which is gradually declining as the baby leaves sucking the breasts.

The main components of this milk are protein, water, lactose, fat, vitamins and minerals.

The pH of milk is: 7 (neutral), and provides 70 to 76 kcal / dl (100ml or 3.5 oz.)

Composition of breast milk

Mainly, breast milk contains 88% water, the quantity the baby needs during the first months, which may explain why babies who are breastfed do not need to drink additional water, even in hot weather. We must not give the baby water or other drinks before six months, as this could trigger diarrhea, infections and other diseases.

Some features of the components of breast milk

Protein: are 0.9% of breast milk, which contains casein, whey proteins, mucins and non-protein nitrogen. These occur in the mammary gland, except for serum albumin, which comes from the maternal circulation. It contains between 30% and 40% casein and 60% whey.

Casein: brings the newborn a dose of amino acids and minerals like calcium and phosphorus. The casein in milk is very digestible; the clots it forms are mild in comparison with thick clots that cow's milk forms.

Lactoferrin: another protein that promotes iron absorption in the intestine and inhibits the growth of pathogenic bacteria in the gastrointestinal tract while taking iron that bacteria need to multiply. Cow's milk has virtually no lactoferrin.

Lysozyme: is the most abundant enzyme in breast milk, and its primary role the development and maintenance of the infant's intestinal flora. This enzyme contains anti-inflammatory properties, is present in 40% in milk and its content is 300 times that of cow's milk.

Lipase: activates the gastrointestinal tract which aids digestion, producing free fatty acids and glycerol. Babies fed with breast milk have a high and highly efficient fat absorption. It also produces a protective effect against bacteria, viruses and protozoa in the antimicrobial action of the enzyme.

Antibodies: breast milk is extremely rich in antibodies, mainly in colostrum, it is rich in Ig A antibodies, which bind to the virus and prevent bacteria from penetrating the intestinal mucosa, in addition to inhibit the colonization of these pathogens in baby's intestine.

Taurine and carnitine: essential for the development and maturation of the central nervous system, retina and good development of the baby. Taurine also aids in the absorption of lipids, osmo-regulation and calcium transport; it is crucial to the formation of bile salts that are essential for digestion. Carnitine is involved in the synthesis of brain lipids.

Carbohydrates: Lactose is the carbohydrate most present in breast milk, providing 40% of calories from breast milk, and is essential for the absorption of calcium, iron, magnesium, etc. Other carbohydrates such as neutral oligosaccharides, glycoproteins, glycosphingolipids, amino-sugars and acetyl are present too.

Minerals: All minerals that a newborn needs are in breast milk, with a very high absorption capacity. The composition of minerals like sodium, potassium and chloride promote baby's kidney function by favoring the metabolic capacity of the newborn.

Calcium and phosphorus: the percentages of calcium and phosphorus in human milk are 2:1, are minerals that are easily absorbed. In cow's milk, phosphorus dominates the match (1:3), which may trigger hypocalcemia in the newborn.

Iron: very easily absorbed when it comes from milk. There are studies that show that iron absorption decreases with the early introduction of solid foods before 6 months of age, then avoid solid foods, in this way anemia and other complications are avoided.

Vitamins: although they cover all the needs of the baby, breast milk vitamin percentages vary depending on the quality of mother's milk due to their nutritional status.
The main vitamins it contains are: A, K, E, D, vitamin B12 (cobalamin), B6 (pyridoxine), B1 (thiamin), folic acid (B9), B3 (niacin) and pantothenic acid (B5). It is recommended for vegetarian mothers to take a B12 supplement as a vegetarian diet does not contain the same sources.

It is also rich in folic acid to synthesize essential amino acids, DNA, RNA and hemoglobin and vitamin C.

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