Breast milk is remarkable in the way that it provides nutrition to your baby. It contains just the right balance of carbohydrates, protein, and fat, as well as antibodies that help fight infections. The composition of your breast milk is designed to change as your baby nurses so that he gets just the right amount of calories and fat. However, sometimes a mom will have problems with what is known as a foremilk hindmilk imbalance. What this means is that she is making (or baby is getting) too much foremilk, the milk from the start of a feeding, and not enough hindmilk, the milk from the end of a feeding.
What is foremilk and hindmilk?
When you nurse your baby, you make only one type of breast milk. Even though milk is described as foremilk and hindmilk, your breasts do not actually produce two separate types of milk.
When you aren’t nursing your baby, your body is constantly making and storing milk for future feedings. Milk is produced in the alveoli (milk making cells inside your breast). It then travels through your milk ducts where it is stored in the lactiferous sinuses (or milk sinuses). When the milk is made, the fatty portion of the milk sticks to the walls of the alveoli. If you’ve ever looked at pumped breast milk after it’s sat in the fridge for a while, you will see that it separates. The fat floats to the top and sticks to the sides of the bottle. This is similar to what happens inside your breasts.
When your baby nurses, he will initially get foremilk from your breasts. This is because the milk that has collected in your milk sinuses is the lower-fat foremilk. As your baby nurses for a while, he will trigger a “let down.” This forceful milk ejection pushes the milk and the fat that is sticking to the walls of the alveoli out. The longer he nurses, the more he will empty out the stored up low fat milk and start forcing the fattier milk out of the alveoli.
The longer the time between feedings, the more foremilk will be stored away inside the milk sinuses. The fat sticking to the walls of the alveoli is still there but your baby won’t get as much of this fat because you will have so much foremilk in storage that any fat will become diluted in the milk. Emptying the breast will empty the foremilk that is stored and allow your baby to get more of the fattier hindmilk.
Why it is important to empty the first breast
Moms are often advised to offer both breasts at every feeding or given a time limit on how long to nurse on each breast. They may be instructed to nurse for ten minutes on the first breast and to then offer the second breast for ten minutes. To make sure your baby gets enough of the fattier hindmilk, you should make sure you empty the first breast first. (See LLLI’s Finish the First Breast First) Don’t restrict your baby to nursing for a certain length of time. Let him nurse for as long as he wants to on just one side. If he pulls off the breast and still seems hungry, you can then offer the second breast.
If your baby is mainly getting low calorie foremilk during his feedings, he will be hungrier and want to nurse more often. Nursing more frequently may compound the problem because mom may develop an oversupply of breast milk. Having an oversupply will mean there will be more milk made –foremilk – that will be sitting in storage between feedings. When this happens, your baby may have a hard time emptying the breasts of the fattier hindmilk because he is getting too filled up with the lower fat foremilk.
Why does this matter? Aside from wanting to nurse more frequently, babies can have other problems when they don’t get enough hindmilk. Breast milk contains lactose, a type of sugar. Your baby’s small intestines produce lactase, an enzyme that digests lactose, but they only produces so much lactase. If your baby is getting a lot of foremilk, he is also getting a lot of lactose. This may be hard on his digestive system. When your baby drinks more hindmilk, he gets more fat, instead of so much lactose, making the milk easier to digest.