Anatomy & Physiology: Mature Milk Components

Mature milk is produced from approximately ten days after delivery up until the termination of the breastfeeding. Mature milk contains on average:

1. Energy (750 kcal / liter)

2. Lipids (38 g / liter) - The main lipids found in human breast milk are the triacyl-glycerols, phospholipids, and fatty acids including essential fatty acids. Maternal diet does not affect the amount of fat in milk but does affect the types of fat. Cholesterol is present in breast milk (more information).

3. Casein (2.5 g / liter) - protein - Casein or curds are proteins with low solubility which complex with calcium. These are present in breast milk in much lower concentration than in cow's milk.

4. Whey (6.4 g / liter) - protein - the whey proteins are located in the clear liquid left behind when clotted milk stands. The largest components are alpha-lactalbumen, lactoferrin, lyzozyme, albumen and immunoglobulins.

5. Nonprotein Nitrogen is used in amino acid synthesis and includes the nitrogen in urea, creatine, creatinine, uric acid and ammonia. Peptides, such as epidermal growth factor, somatomedin - C and insulin are also present in this fraction. Nucleotides such as cytidine monophosphate are derived from nucleic acids and play an important role in the immune system and protein synthesis.

6. Lactose (70 g / liter) carbohydrate - Lactose is the major carbohydrate in breast milk. It is composed of galactose and glucose. Lactose concentration in breast milk increases over the duration of breastfeeding.

The amount of all of these substances (except lactose) varies with the time of day of the breast milk production, the woman producing the breast milk, and whether it is at the beginning or the end of the feeding. Fats and lipids are particularly high at the end of the feeding (hind milk) ( Lawrence, 2005 p105-170, Hamosh, 1992 , Slusser, 1997 ).