The Composition of Breastmilk, Part 1

Most everyone knows that “breast is best” for baby. But why? What makes it so special? In this two-post series, we’ll take a look at what breastmilk is made of. In part 1, I’ll share information on colostrum and transitional milk, part 2 will present more on mature and involutional milk.

The Composition of Breastmilk: An Overview

Breastmilk composition is constantly changing. Its makeup and taste depend on many factors, including how and when nurslings nurse, the time of year, where the mother lives, and what the mother eats. (1) Breastmilk contains “growth factors, hormones, enzymes, and other substances that are immune-protective and foster proper growth and nutrition . . . .” (2)

Recent scientific discoveries have revealed that breastmilk is the only adult tissue that has more than one type of stem cell present. The implications of this fact are being explored, but there is preliminary evidence that these stem cells specifically promote bone and muscle growth in nursing infants. Scientists also hypothesize that “a mother’s mammary glands tak[e] over from her placenta to guide infant development once her child is born.” (3)

Breastmilk really is the original super food.

One of the most obvious differences in composition depends on what type of breastmilk we are talking about. There are really four different kinds of breastmilk: colostrum, transitional milk, mature milk, and involutional milk.

Here, a newborn latches on for the very first time - he will reap the benefits of colostrum and breastmilk for a lifetime! Thank you to Allison at for sharing this beautiful image.
Here, a newborn latches on for the very first time - he will reap the benefits of colostrum and breastmilk for a lifetime! Thank you to Allison at for sharing this beautiful image.


Colostrum is the thick, yellowish milk that can start to appear during pregnancy. Before birth, your baby receives the nutrients it needs to grow and develop through the placenta; after birth, your colostrum and milk take over. (1)

“Colostrum is a living fluid, resembling blood in its composition. It contains over [sixty] components, [thirty] of which are exclusive to human milk. It is species-specific, designed for human babies.” (2) Among these sixty components are immunoglobulins, high amounts of lipids, milk fats, and protein, high levels of beta-carotene, and high concentrations of leukocytes. (3) Each component has a specific function to nourish and protect your newborn. Here are a few of the reasons your baby will benefit from colostrum.

1) Colostrum is the Only 100% Safe Vaccine

As soon as your baby is born, bacteria begin to colonize on his skin and in his mucous membranes. Newborns are more susceptible to the negative effects of bacteria and viruses, but colostrum offers protective immunities. Colostrum is rich in immunoglobulins, which produce antibodies specific to the environment. These antibodies also continue to provide “the passive immunities that were provided in utero by the placenta, such as poliovirus and rubella.”  (4) The high concentrations of leukocytes found in colostrum can actually “destroy disease-causing bacteria and viruses.” (5)

2) Nature’s Finest Painter

Besides producing antibodies to protect newborns against infection, colostrum also protects by helping to “seal” a newborn’s intestines. A new baby’s intestines are very permeable. Immunoglobulins in colostrum “‘paint’ the lining of the infant’s stomach and intestines. These surfaces are then able to defend the baby against viruses and bacteria by not allowing pathogens to adhere to them. Some of these incredible immunoglobulins actually attack pathogens and kill them.” (6)

3) Because You Want to Get Past the Meconium Stage

When your baby is born, her stomach is the size of a marble. This is why she wants to nurse so often – not only does she not eat much at any one feeding, but colostrum is also easily digestible, so it passes quickly through her system. Colostrum has a laxative effect on a newborn, and it will help your baby pass meconium (baby’s first poo).

Passing meconium is important to rid your newborn’s body of excess bilirubin and prevent jaundice. When the meconium has passed, your baby’s stomach will then grow to the size of her fist, and she will start nursing (and ingesting) more milk. (7)

Interestingly, colostrum is not on a supply/demand schedule – the amount of colostrum your body produces is hormonally driven, it is not related to how much your newborn nurses. This is in direct contrast to mature milk: your body will make more the more your baby nurses. (8)

4) Colostrum Encourages Optimal Development of the Brain, Heart, and Central Nervous System

Colostrum is high in several nutrients that assist in the cell membrane production necessary for growth and development of the brain, heart, and central nervous system. These nutrients include sodium, potassium, milk fats, chloride, and cholesterol. (9)

One truly amazing fact about colostrum is that the amount of certain nutrients changes depending on whether the newborn is term or premature. For example, the amount of certain lipids and milk fats are significantly higher in the colostrum of mothers with preterm babies; these substances are vital in helping the underdeveloped newborn “catch up” in terms of growth and brain and retinal development. Some of these nutrients remain at higher levels for as many as six months after a premature birth – our bodies are phenomenally designed to give our babies the perfect nutrition. (10)

5) It’s the Perfect – and Only – Food Your Newborn Needs

Colostrum is saturated with fat-soluble vitamins and minerals. It is often a yellow or orange color, reflecting the high levels of beta-carotene, one of the many antioxidants present. Antioxidants act as cell protectors in the infant’s body and enhance his immune system.” Colostrum is high in proteins for nutrition and to regulate blood sugar. (11)

Colostrum provides the ideal, easily digestible nutrition that your newborn needs. It protects your newborn from illness and helps develop her immune system. Colostrum is delivered in the perfect amount for your newborn’s tiny stomach – it is measured in teaspoons rather than ounces. (12)

Under normal circumstances, the vast majority of women can breasteed – there is rarely a need to supplement with formula. (13) “[E]ven one supplemental bottle of artificial infant milk can sensitize a newborn to cow’s milk protein. Formula changes the gut flora in breastfed babies by breaking down the mucosal barrier that colostrum provides them. This violation allows pathogens and allergens entry into the baby’s system.” (14)

There is nothing more beautiful than a contented nursing pair. Photo credit:
There is nothing more beautiful than a contented nursing pair. Photo credit:

Transitional Milk

As its name implies, transitional breastmilk is the milk you produce while your body transitions from colostrum to mature milk. (15) A woman may produce transitional milk for up to two weeks after childbirth, longer if she gives birth prematurely. (16) While colostrum is hormonally driven, transitional milk marks the beginning of breastmilk’s supply/demand production – a mother’s “breasts are stimulated to produce transitional milk by breastfeeding her baby regularly, about every 2 hours.” (17)

Transitional milk is really just a mixture of colostrum and mature milk. It has high levels of lipids necessary “for growth, brain development, and salt synthesis[,]” proteins needed for nutrition and blood sugar regulation, fats and lactose for calories, energy, brain development, and retinal function, and water-soluble vitamins. (18)

Please check back for Part 2 to learn more about mature and involutional milk!


(1) Prentice, Ann, “Constituents of Human Milk,”
(2) Hamosh, Margit, PhD, “Breastfeeding: Unraveling the Mysteries of Mother’s Milk,”
(3) “Stem cells could be the secret reason why breast is best,”
(4) The Importance of Colostrum (citing Hanson, L.A. Immunobiology of Human Milk: How Breastfeeding Protects Babies. Amarillo, TX: Pharmasoft Publishing, 2004)
(5) What Is Colostrum?
(6) The Importance of Colostrum (citing Alm, J. et al. An anthroposophic lifestyle and intestinal microflora in infancy. Pediatric Allergy and Immunology 2002; 13(6):402); What Is Colostrum?
(7) The Importance of Colostrum; What Is Colostrum?
(8) “How Does Milk Production Work,”
(9) Breastfeeding: Unraveling the Mysteries of Mother’s Milk; The Importance of Colostrum (citing Oddy, W. The impact of breastmilk on infant and child health. Breastfeeding Rev 2002; 10(3):5-18; Rivers, L. The long-term effects of early nutrition: the role of breastfeeding on cholesterol levels. J Hum Lact 2003; 19:(1))
(10) Of course premature infants may need to be supplemented to assist in their growth and development. Breastfeeding: Unraveling the Mysteries of Mother’s Milk
(11) The Importance of Colostrum (citing Hanson, L. and Korotkonva, M. Breast-feeding may boost baby’s own immune system. Pediatric Infectious Disease Jour 2002; 21:816-821)
(12) What Is Colostrum?
(13) “Still More Breastfeeding Myths,”
(14) The Importance of Colostrum (citing Kalliomaki, M. and Isolauri, E. Role of intestinal flora in the development of allergy. Curr Opin Allergy Clin Immunol 2003; 3(1):15-20;  Ogawa, K. et al. Volatile fatty acids, lactic acid, and pH in the stools of breast-fed and bottle-fed infants. J Pediatr Gastroenterol Nutr 1992; 15(3):246-7); see also for other risks of using formula instead of breastfeeding
(16) As noted in my earlier post on colostrum, mothers of premature infants continue to make breastmilk that has the qualities of colostrum and transitional breastmilk for a much longer period – up to six months. Hamosh, Margit, PhD, “Breastfeeding: Unraveling the Mysteries of Mother’s Milk,”
(17) “How Does Milk Production Work,”;,,ue5267,00.html
(18),,ue5267,00.html; Hamosh, Margit, PhD, “Breastfeeding: Unraveling the Mysteries of Mother’s Milk,”

Author: Dionna

Dionna writes at Code Name: Mama, where she shares information, resources, and her thoughts on natural parenting and life with a toddler/preschooler.

9 thoughts on “The Composition of Breastmilk, Part 1”

  1. THANK YOU for posting this! I am a breastfeeding advocate and the more information I find the better. Every should pass this and information along with information to a mother with doubts or who needs encouragement.

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