Composition of Breast Milk

Composition of Breast Milk

composition of breast milk
The composition of breast milk is always changing. It changes depending on:

  • whether you are at the beginning or end of a feeding session;
  • how old your baby is; and
  • other factors like your diet.

Breast Milk Changes over one Feeding Session

During each feeding session, the milk that comes out of the breast first is called foremilk and it is quite watery. Milk coming out later is called hindmilk and it is creamier and may have 50% more fat.

Your breasts make one kind of milk but, its composition will depend on how long the milk has been sitting in your breasts. This is because fat sticks to cell membranes. So breast milk that is left-over from the previous feeding will be more watery because the fats have stuck to the cell membranes. Freshly made milk that comes after let-down will have the full complement of fats because the fat has not had time to stick to the cell membranes yet.

Some people suggest that one of the jobs of foremilk is to quench Baby’s thirst. The job of the high-fat hindmilk is to fill Baby up and signal to him to stop sucking. It has even been suggested that the high-fat hindmilk is like a rich creamy dessert at the end of a meal. Suffice to say that the composition of breast milk changes during one feeding session.

breast and breast milk

1. Breast milk is made at the alveoli. This milk comes after let-down and is called hindmilk.
2. Milk from the previous feeding session is stored in the Milk Pools (right under the areola). This foremilk has less fat because the fat has had time to stick to the sides of the cells.

Some women produce too much milk. This is a problem because too much milk will lead to too much left-over milk. At the next feeding, Baby will fill-up on the excess watery foremilk, but not have access to the high-octane hindmilk. When this happens, it will cause an imbalance in Baby’s diet.

To fix the problem, breastfeed from one breast only. At the next feeding session, alternate to the other breast but again feed from this breast only. Feeding from one breast only will give Baby a chance to drinking past the foremilk and into the hindmilk. By leaving one (or the other) breast full (engorged), it will signal your body to make less milk. In time, things will even out and you won’t overproduce.


Breast Milk Changes from Month to Month
Mother’s breast milk changes over the period of a few months too. These changes in composition parallel the changes in babies needs. changes in breast milk composition

  • Colostrum is made during late pregnancy and during the first week after child birth. It has three times as much protein as the mature milk. Colostrum has more antibodies, less sugar, and less fat compared to mature milk.

    The goal of this early-milk is to provide Baby with immunity factors to fight germs and bacteria. This makes sense: Baby didn’t have to fight germs when he was in your womb. Now that Baby is out of the womb, it is important to give him antibodies since his own immune system has not developed yet.

  • Transitional Milk is the milk made after colostrum and before mature milk (sometime between day 4 and day 10 after birth). Its composition is somewhere between that of colostrum and mature milk.

  • Mature milk is mostly water. If you removed all the water, you would be left with
    – carbohydrates (55%),
    – fats (37%),
    – proteins (8%), and
    – various elements such as minerals, vitamins, and enzymes.

  • Mature milk continues to change over the course of the first year: nutritional composition of breast milk will gradually decrease 10% to 30%. After 6 months of age, you should introduce solid foods to accommodate the changes in your breast milk.

Now that we know the composition of breast milk changes constantly, let’s talk about the components in greater detail. What do the fats, carbohydrates, and proteins do? Why are they important for Baby’s healthy and development? How do baby formulas compare to the composition of breast milk?