The Composition of Breast Milk

Guest Author – Jessica Gunsch

Breast milk is an extremely complex food with hundreds of ingredients and ever changing combinations and concentrations. For this reason it is very difficult to mimic this composition with formula which for one thing does not contain the critical antibodies and enzymes found in breast milk.

During the first five days of your baby’s life outside the womb, he or she is nourished on colostrum. This first milk is clear or yellow and barley noticeable but it is an invaluable substance that gives your baby a healthy head start in life second to none. Between two and five days (possibly sooner after the first child) colostrum begins to be accompanied by mature milk which is when your milk ‘comes in’. At this point you will probably notice more fluid either visibly or by the sheer weight of your breasts. At ten days or soon after, the colostrum disappears and mature milk is established.


Often termed ‘liquid gold’, colostrum is made up of rich concentrations of essential proteins called globulins. It is also high in sodium which is the only substance that globulins are soluble in. Colostrum is relatively low in fat and sugar compared to mature milk. It begins to be produced during pregnancy and you may have even noticed a bit of leaking before birth. In the first days after your child is born only about 100 cc of colostrum is released. Though this seems like a small amount, it is entirely sufficient for your baby and in fact any kind of supplement should be avoided to fully reap the benefits of colostrum. Some of the proteins provide the child with the mother’s antibodies giving him or her immunity to certain illnesses within the first few hours of life and throughout the breastfeeding experience.

Mature milk:

Mature milk contains proteins, vitamins and minerals, lactose (sugar), fatty acids, antibodies and enzymes that aid in digestion and absorption. The concentrations of these components vary specifically to meet your baby’s changing needs. The composition of breast milk changes even within the course of a feeding. At the beginning of a feeding your baby receives foremilk, which consists of hydrating fluid to satisfy thirst. After a few minutes, a transition to hind milk occurs which contains the fat and calories necessary to your baby’s nutrition. It also changes throughout the course of a day where milk produced in the morning is very different than the milk produced at evening feedings and it changes from day to day with your child’s increasing age.

One of the most fascinating things about the power of breastfeeding is that the child’s mouth can actually affect the composition of breast milk. If a child has been exposed to an illness for example, the bacteria or virus will be detected from the child’s mouth and the milk will be produced accordingly with the antibodies necessary to protect the child even before mom herself receives the immunity. It never ceases to amaze me how my preschooler can bring home a cold and everyone in our home except the baby gets sick!


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