BREASTFEEDING

Human breast milk is uniquely composed to meet the needs of human infants:

1. It has a high concentration of lactose (milk sugar). This is an excellent source of carbohydrates.
2. There are 3 different categories of proteins in human milk: whey proteins, casein proteins, and non-protein nitrogen. The predominant type of protein in cows milk is the casein protein (curds). The whey proteins which are predominant in human milk are much easier for infants to digest. The whey/casein ratio in human milk decreases from 90/10 in colostum, to 60/40 in mature milk and to 50/50 in late lactation ( Lawrence, 2005 pgs. 127-135).
3. Infants fed human milk tend to have stools that are less foul smelling and softer than those of infants who are fed cow's milk or soymilk based formula. This is due to the different bacteria in the gastrointestinal tract of infants who are solely breast fed. Constipation, defined as hard stools (not the absence of a daily stool), does not occur in healthy breast fed infants.

The stool of a healthy breastfed baby
(picture courtesy of Wellstart International)

4. The composition of the milk of mothers who are breastfeeding varies during the time of the day and during the feeding. The hind milk (latter part of a breastfeeding) has a much higher fat content than milk produced during the beginning portion of the feeding. ( Lawrence, 2005 pgs. 106-110).
5. The odor and/or taste of breast milk may change depending on the mother's diet. This may help infants get used to different tastes ( Mennella, 1991 ).
6. More information on nutritional factors in breast milk is found in the section on 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