Composition of Milk

The composition of breast milk changes greatly from its first nutritious drops to rich, mature milk.

  • It is well suited to completely nourish infants without any need for supplements, other than previously mentioned, or formula.
Images courtesy Rebecca Behre, RNC, IBCLC, Gritman Medical Center, Moscow, Idaho

The first milk is known as colostrum and is produced while a mother is still pregnant, approximately 12 weeks before delivery.

  • Thick and yellow in color, colostrum is considered to be “liquid gold.”
  • Though only produced in small quantities (typically 5-10 mL per feeding but can range from 2-20 mL per feeding), colostrum is well suited for an infant’s immature digestive system.
  • Rich in protein and minerals and low in fat and carbohydrates, colostrum provides ideal nutrition during a newborn’s first 24 to 72 hours of life.
  • This milk has both sIGA passive antibody protection as well as anti-idiotypic active protection.
  • In addition, there are over 45 identified bioactive substances in colostrum that serve to program the newborn’s immune system
  • Colostrum acts as a laxative aid for passage of meconium, an infant’s first bowel movements.

According to the ABM Clinical Protocol #3: Supplementary Feedings in the Healthy Term Breastfed Neonate 40 , the average reported intake of colostrum, term breastfed infats are as follows: 

  • 1st 24 hours = 2-10 mL/feed
  • 24-48 hours = 5-15 mL/feed
  • 48-72 hours = 15-30 mL/feed
  • 72-96 hours = 30-60 mL/feed

Transition milk serves as a bridge between colostrum and mature milk.

  • This milk is produced in higher volume than colostrum.
  • Its content is lower in proteins and immunoglobulins, but higher in calories, fat, and lactose levels compared to first milk.

The composition of mature milk’s changes throughout an infant’s feeding; it also changes as the infant’s needs change as she/he grows.

  • Foremilk is provided when the breast is full and has a lower fat content.
  • Hindmilk is provided when the breast is nearly empty and has a higher fat content, which increases infant satiety and contains fats needed for healthy weight gain.
  • The baby should empty the breast before switching to the other breast to ensure that the baby is getting the hind milk with the higher fat content along with the foremilk.
  • Regardless of how healthy a mother’s diet may be, she will generally produce nutritious milk for her child. Of course, mothers should be encouraged to maintain a balanced diet for their own health and well-being.
  • The size of an infant’s stomach dictates how much milk the baby can comfortably drink. Milk production closely parallels the amount of milk baby requires.