All About Breast Milk


Breast milk comprises of all the nutrients that a baby can possibly need for the first 6 months at least. It contains water, proteins, fat, carbohydrates, necessary vitamins, and minerals in adequate quantities.

Mature human breast milk is composed of the following:

Fat: 3-5%

Human milk has high content of palmitic acid and oleic acid. It also has a good number of phospholipids. Breast milk contains long chain polyunsaturated fatty acids(docosahexaenoic acid or DHA, and arachidonic acid or ARA) which are not found in any other sources of milk. DHA and ARA play a huge role in augmenting the development of the baby’s nervous system.

Protein: 0.8-0.9%

In colostrum the protein content is slightly higher, when compared to the carbohydrate level.

Protein constituents of human breast milk are as follows: casein, alpha-lactalbumin, lactoferrin, Immunoglobulin IgA, lysozyme and serum albumin, enzymes, minor proteins, and essential amino acids – all which meet the requirements of a human infant.

Carbohydrate:  6.9-7.2%

Principal carbohydrate present in the human milk is lactose, along with 30 or more Oligosaccharides. Some of these sugars, control the intestinal flora of the baby to promote the growth of certain bacteria like lactobacilli.

Minerals: 0.2%

Sodium, potassium, magnesium, calcium, phosphorus, and chorine.

Iron, copper, zinc, and other trace elements.

Nitrogen: about 25% of nitrogen comprises of nonprotein compounds like urea, uric acid, creatine, creatinine, and a large number of amino acids.

Vitamins: all vitamins are found in the human milk insufficient quantity except vitamin D.

Energy: 60-75 kcal per 100 ml of mature human milk.


Antibodies also known as immunoglobulins are protein compounds formed by the bodies immune system on exposure to pathogens like bacteria, virus, and other microorganisms. They provide protection to the body by fighting infections and illnesses. They are found in the saliva, sweat, blood and even the human breast milk.

There are five types of antibodies found in the human body – IgG, IgD,IgE, secretory versions of IgM, and IgA.

The human milk has all of these but more of IgA – known as secretory immunoglobulin.

All these antibodies together help in fighting infections in babies, both premature and term born– particularly so because babies have a very weak immune system. It develops over time and needs the necessary nourishment until then.


Colostrum has extremely high levels of Secretory IgA, when compared to other phases of milk.

IgA forms a protective layer over the nose, throat, and the gut. This protective layer over the mucosal lining helps fight illnesses caused by bacteria, virus, fungi, and parasites. It also protects the organs from the acidic fluids released into the gut, and from all the enteric bacteria. Since the respiratory and the digestive tracts are a path of communication to the external environment, they need the maximum protection.

All the antibodies combined prevent eczema, milk allergies, wheezing in babies. Those who have a family history of asthma and allergies are also benefitted.

Breast milk has white blood cells which prevent infections.

It also has whey proteins (lactoferrin and lysozyme) which can kill unwanted micro-organisms.

Oligosaccharides in the breast milk prevent the bacteria from attaching to the mucosal layer of the intestines or respiratory tract.

Vitamin A in the breast milk is important for healthy eyes and to maintain the integrity of the epithelial layers of the body.

Breast milk is so potent that it protects the baby from illnesses acquired by the mother except for a few like HIV etc.

Breast milk prevents ear infections, respiratory tract illnesses, intestinal tissue damage, diabetes, childhood leukemia, Inflammatory bowel disease and reduces the risk of obesity in the future.

Breast fed babies are less likely to develop colic or abdominal discomfort or indigestion.


Breast milk has three phases:

  1. Colostrum: The first yellowish colored milk secreted by the mother is known as colostrum. It lasts only for 2-3 days as soon as the mother starts lactating, post parturition. It is referred to as liquid gold by doctors because of its amazing property of immunity boosting when given to the baby. It is highly rich in nutrients and has a large quantity of IgA antibodies which protects the baby against allergies – effective immediately. Colostrum nourishes the baby’s digestive tract.

It is also rich in fat soluble vitamins like A, E, and K.

  • Transition milk: Transition milk is formed between 2-5 days of childbirth and lasts for 2-3 weeks. It has all the necessary nutrients required by the child for nourishment and a healthy growth. The color of the milk in this phase changes to white with a slightly yellowish tinge. The breasts become warmer. Expressing milk regularly will increase the production of milk and avoid engorged breasts.
  • Mature milk: After 2 weeks of childbirth, this phase of milk production occurs. The amount of fat in the milk changes as it matures as required by the baby. To ensure that wholesome nutrition is provided to the child, make sure that the baby is fed from both the breasts – although the constitution is almost same, unless one of them is infected.


Breast milk starts forming in the second trimester around 15 weeks pregnant.

Colostrum or the first milk is expressed immediately after parturition but for some women chances of a let-down are possible during pregnancy.

Increased level of hormones not only stimulate the growth of hormones, but also the milk ducts.

Production of milk after the first few days is entirely dependent on the baby’s needs. As the stomach of the baby is small, and digestion is slow, the production of milk is less, but it increases with the demand.

To avoid engorged breasts and to increase the production of milk – it is important to regularly pump milk or express it in both the breasts.


Two major hormones play an important role in breastfeeding – prolactin and oxytocin.

When the baby starts sucking on the nipples, sensory input reaches the brain. In response, the anterior pituitary gland secretes prolactin and the posterior lobe releases oxytocin.

Prolactin is necessary to produce milk in the cells of the alveoli.  It also helps in the growth and development of the mammary tissue.

 The level of prolactin in the blood increases rapidly during pregnancy. It is required to produce milk and maintain and develop both the mammary glands for lactation. But due to high levels of estrogen and progesterone, the milk is not expressed out of the glands. They block the secretory action of prolactin.

But soon after birth, the levels of estrogen and progesterone decrease, causing the secretory action of prolactin dominate and release milk from the milk ducts.

With the suckling action, prolactin increases thus increasing the milk production. First few weeks of pregnancy the level of prolactin is directly proportional to the amount of milk produced.  More prolactin is produced in the night, therefore breastfeeding in the night will help in keeping the supply of breast milk high. If the mother stops breastfeeding, the production of milk stops and dries up.

Suckling effect, especially at night increases the release of other pituitary hormones – gonadotropin secreting hormones, luteinizing hormones and follicle stimulating hormones. These prevent ovulation and menstruation and thus the chances of another pregnancy are considerably lowered during breastfeeding.

Oxytocin causes the contraction of the myo-epithelial cells around the alveoli. This contraction causes the milk to flow along the ducts and express out of the nipple. This is known as oxytocin reflex or let down reflex or milk ejection reflex.

Oxytocin is produced before the mother begins a feed. It is released more easily than prolactin. It is dependent on the mother’s feelings and sensations. Skin to skin contact causes the reflex to happen.

Signs of an active oxytocin reflex include a tingling sensation around the nipple, pain in the uterus, milk flowing from either or both breasts when she thinks of the baby crying, thirst during a feed, blood flow from the uterus, milk streaming down form the other breast while the baby is latched on to one.

Oxytocin is a stress reliever and produces a sense of calm in the mother.

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