CG The Changing Composition of Breast Milk -

The Changing Composition of Breast Milk

Breast milk is often celebrated as the best nourishment for babies, but did you know it’s constantly evolving? From the moment your baby is born, your milk adapts to meet their changing needs. This amazing fluid isn’t just “milk”; it transforms to provide the perfect balance of nutrients and protection at every stage of your baby’s growth. Understanding how your breast milk evolves over time can deepen your appreciation for this unique and irreplaceable gift that only you can provide.

What’s In Breast Milk?

- Water: Keeps your baby hydrated
- Carbohydrates: The main form is lactose, which gives your baby energy
- Fats: Provide energy and are vital for growth and development
- Proteins: Help your baby grow and fight off illness
- Vitamins and Minerals: Keep your baby healthy and strong
- Hormones and Growth Factors: Regulate your baby’s metabolism, sleep cycles, and contribute to healthy weight gain during infancy and beyond
- Healthy Bacteria: Pre- and probiotics coat the lining of your baby’s intestines to aid in digestion, keep them healthy, and decrease their risk of allergies

How Breast Milk Changes the Month

Colostrum: Colostrum is the first milk your baby consumes after birth. It is packed with nutrients and antibodies that help coat your baby’s gut, fight infections, and protect your baby from illnesses and allergies. It is high in protein, vitamins, minerals, and antibodies. It is often called “liquid gold” because of its rich, golden color and valuable benefits.¹ Your body begins producing colostrum in the second trimester of pregnancy, between 12 and 18 weeks.² While your breasts may not feel full the day your baby is born, newborns have tiny tummies, and you already have enough colostrum to nourish your baby. For example, an average feeding on Day 1 is between 2 to 10 mL.³ Your body will continue to produce larger amounts of colostrum each day for the first week or so after delivery. Signs that breastfeeding is going well.
Transitional Milk: Transitional milk begins to increase in volume by Day 3-5 postpartum. Your breasts will feel heavier and fuller as your body begins to make more milk.
Mature Milk: The milk your baby gets after the first couple of weeks is called mature milk. It’s lighter in color and consistency than colostrum or transitional milk and contains the perfect balance of proteins, fats, and carbohydrates for your baby. By 4-6 weeks most mothers have reached maximum milk supply, which is on average between 25-35 ounces per day.

How Milk Changes Each Day

- Milk Changes Between Feedings: The composition of your breast milk differs every time you feed your baby. Depending on how long your baby eats and how long it’s been since their last feeding, the volume of milk and calories they receive can vary. Strongly flavored foods, such as garlic, can change the taste of your breast milk. Research has shown that the change in the flavor of breast milk can influence a baby’s acceptance of new foods once they are introduced to solids.⁴

- Milk Changes Throughout the Feeding
  - Foremilk: The milk your baby gets at the beginning of the feeding is higher in carbohydrates, which makes it sweeter, and lower in fat, which helps quench your baby’s thirst.
  - Hindmilk: As your breast empties during the feeding, your milk increases in fat and calories. This milk helps your baby easily digest the carbohydrate-rich foremilk and feel full.
  - Balance: With at least 8 feedings per day, your baby should have plenty of opportunities to get the right balance between foremilk and hindmilk without any special effort. Sometimes, mothers with an oversupply of breast milk find that their babies get “lactose overload” from too much foremilk and show symptoms such as gassiness and green, watery stools. This is rare and can be improved with help from a Lactation Consultant.
- Milk Changes Between Daytime and Nighttime: Newborns often have their days and nights mixed up, sleeping longer stretches during the day and being more alert at night. One reason is that babies don’t produce their own melatonin for the first few months. Breastfed babies receive higher concentrations of melatonin through their mother’s milk at night, which may help them sleep longer. One study showed that breastfed babies slept on average 40-45 minutes more per night than babies receiving formula.⁵

How Breast Milk Changes as Babies Get Older

Protein Ratios Shift: As your baby grows and their nutritional needs change, the composition of breast milk gradually adjusts. The concentration of certain nutrients, such as the ratio between whey proteins and casein proteins, changes as your baby’s digestive system matures. During the first month or so, the ratio of whey proteins to casein proteins is about 90:10. By about 6 weeks, the ratio is 80:20 and by 6 months, it is 60:40. In later lactation it is about 50:50.
Increase in Fat: As babies start weaning, breast milk’s composition changes as milk supply decreases. The fat content in breast milk of babies nursing past a year has been found to be up to 50% higher than the milk received by younger nursing babies.⁶
Reduction in Some Nutrients: In babies breastfeeding longer than 18 months, carbohydrate content decreases in breast milk as babies receive more of their calories from solid foods.
Continued Immune Support: As weaning progresses, the concentration of antibodies to bacterial and viral diseases increases to protect babies as they are introduced to new foods and surroundings.

Different Milk for Baby Boys and Girls?

There may even be differences in breast milk composition depending on if you have a baby boy or girl! We know that baby boys tend to grow faster than baby girls and may have different hormonal and caloric needs because of variations in metabolism and growth patterns. The World Health Organization even provides different growth charts for boys and girls. Emerging evidence suggests that some of this variation may be due to differences in the composition of their mother’s milk. While most of the research has been done in non-human mammals, there is evidence that there may be sex differences in the milk humans produce as well.⁷

What If I Have Questions?

If you are interested in learning more, these Aeroflow classes expand on some of the topics discussed above:

Birth & Breastfeeding
Ultimate Breastfeeding Prep

To register for these classes, log into your portal or click here.

Want More Info?

For a directory of Aeroflow’s other Care Guides offering information on pregnancy, baby care, and more, browse our comprehensive list of titles:

https://www.hersourcehealth.com/aeroflow-care-guides/ ‎

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