Getting to Know the Three Phases of Breast Milk

Your body is amazing. Not only did it grow and birth a human, but it is also capable of exclusively nourishing that human through the first six months of their life. Did you know that as your baby grows and changes, your breast milk grows and changes, too? Yup, that’s right. Your body knows exactly how to create the perfect, most nutrient-rich formula to protect and help your little one grow. So today, let’s spend some time getting to know the three phases of breast milk.

Phase 1: Colostrum

Colostrum, otherwise known as “liquid gold,” is the precursor to your milk supply and produced for only 2-5 days postpartum. A nutritionally dense superfood for babies, colostrum contains white blood cells and immune-boosting support. Colostrum is high in protein but low in sugar and fat, making it easier for your newborn to digest. Colostrum is so beneficial to your newborn, you should make giving it to them a priority, even if you don’t plan to breastfeed.

Some women can produce colostrum throughout their pregnancy but don’t worry if you don’t notice any. Once the placenta is expelled from the uterus, hormonal shifts signal to the breasts that it’s time to start production. Colostrum is noticeably different from breast milk. It is thick, creamy, and typically gold/yellowish in color (but it can be clear). One thing you may notice is that you will produce far less colostrum than you will transitional or mature milk.

A feeding for your newborn will consist of about 1-1.5 teaspoons of colostrum. While this sounds like a dramatically small amount, your newborn’s stomach is quite small and does not begin to stretch until around day three. By this time, your baby will be capable of eating more per feeding, and, luckily, this is when your transitional milk will come in.

Phase 2: Transitional Milk

Typically, between days 3-6 postpartum, you will begin to produce “transitional” milk, the bridge between colostrum and mature milk. Your newborn is growing rapidly during the first few weeks of their life, and amazingly, your breast milk adapts to meet their changing needs. During the time of your transitional milk, your breasts are learning how much to supply based on how much your newborn is eating.

The content of your milk at this stage is changing, too. Compared to your colostrum, transitional milk has a higher content of fat and lactose (sugar), which helps give your baby energy. The protein content of your transitional milk changes, too. Casein and whey now play important roles in digestion and satiety. Whey proteins, which are rich in antibodies and remain liquid in your baby’s stomach. This makes them easily and quickly digestible. Casein protein, however, curdles when it mixes with the acid in your baby’s stomach, helping them feel fuller longer. If you begin to notice chunks in your baby’s spit-up, this is why.

Your breast milk changes the most during this transitional phase as your body learns how to match the changing needs of your growing newborn. By the end of your first month postpartum, your milk supply will transition into your mature milk.

Phase 3: Mature Milk

Your final stage of breast milk transition is your “mature” stage, typically reached by four weeks postpartum. At this point, your milk has made almost all of the changes and adaptations necessary to meet your growing baby’s needs. Your mature milk is especially effective at protecting your little one against bacteria. Perfect timing, too, as we’re sure you’re noticing your little one putting more objects into their mouth! Interestingly, your mature milk is so specifically suited for your unique baby, scientists are still having trouble fully understanding exactly which cells, antibodies, etc. breast milk is made of and how it works to protect babies. Amazing.

Mature milk is delivered to your baby during feedings in two stages: foremilk and hindmilk

    • Foremilk is the milk that comes out at the beginning of your feed. It is thinner, sweeter, and typically lower in fat. 
    • Hindmilk is the milk that comes in gradually as your baby continues to feed. It is more nutritionally dense and higher in fat.

Your mature breast milk not only satiates your baby’s hunger, but it also helps build their gut bacteria, boost their immune system, and feeds their rapidly growing brain. On top of that, your mature breast milk contains stem cells and hormones that help build the foundation for your baby’s health throughout their entire life!!

If you are experiencing difficulty with breastfeeding, have questions, or just need some support, we offer a variety of  lactation consultation packages, including virtual appointments!

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