What’s in Breastmilk?

Published on December 15th, 2020

So much about being a mom is extraordinary. From hearing your baby’s heartbeat for the first time to the intensity of your pregnancy cravings (double cheeseburgers with extra pickles… like more pickles, please), you’re learning all the amazing things that your body is capable of. 

Possibly the most miraculous of your body’s changes? The ability to produce breast milk.

You’re making a tiny human being and providing the nourishment she needs to grow from a newborn to a terrific little toddler. Face it—you’re a one-woman miracle machine.

You might be wondering, what’s in breast milk and what makes it so special for your little one? 

Got Milk? A Crash Course in Breastmilk Production 

Throughout your pregnancy, your body gears up to start producing mother’s milk. Milk production comes down to two sets of hormones.

Stage 1: Estrogen and Progesterone 

Also known as the pregnancy hormones, estrogen and progesterone are responsible for many changes in your pregnant body—particularly in your breasts. Estrogen and progesterone cause:

  • An increase in milk ducts and milk-making tissue in your breasts—yup, you have estrogen and progesterone to thank for your new cup size. The increased ducts and tissue help ensure maximum milk production.
  • Increased blood flow to your breasts, causing veins to become more visible and creating additional paths for nutrients to flow into your milk-making tissue. 
  • Enlarged and darker nipples and areola. Some scientists theorize that this change in your body helps babies lock on to the “bullseye” a bit better. 

Stage 2: Prolactin and Oxytocin 

After your baby is born, estrogen and progesterone take a backseat to two new hormones—prolactin and oxytocin. Each have their own functions when it comes to making breast milk:

  • Prolactin sends signals to your mammary glands (your milk-making glands) to start producing your child’s first favorite food. Thanks to the increased blood flow to your breasts, the milk glands use nutrients in your blood to formulate your breast milk supply.
  • When your areola is stimulated by your baby’s suckling, oxytocin is released. This sends a signal to your brain that it’s feeding time and the baby is hungry. In turn, this triggers the “let-down” effect, which is when the mammary alveoli—the small sac found in the mammary gland that controls the release of milk—contracts, allowing a flow of milk to fill your baby’s tummy. 

How your body creates human milk is pretty amazing. But after all that hard work, what’s in the end result? 

The Big 4: Macronutrients in Breast milk 

What’s in breast milk? Basically everything your child needs at this crucial stage of life to develop in healthy ways, starting with the big four micronutrients: water, carbs, lipids, and proteins.

#1 Water

You’ve probably heard this fun fact: a human adult is about 60% water. So really, calling water “the elixir of life” might be an understatement. Water helps organs function, regulates the body’s temperature, and keeps our blood—aka the body’s pipeline of nutrients—flowing smoothly. This is why it’s so important for your child to get proper hydration in the earliest part of life.

Good news, your breast milk is your child’s biggest source of hydration. In fact, human breast milk is 88% water. A mother’s milk helps your child get all the water she needs to support her growing body. 

#2 Carbohydrates 

When you hear “carbohydrates” you might think of bread, pasta, and doughnuts (anybody else hungry?). But carbs come in all shapes and sizes. It’s a biomolecule that naturally occurs in sugars, starches, and fiber. 

It’s also the preferred energy source for your baby’s growing brain—and trust us, that brain needs tons of energy. At birth, your child’s brain is about 33% the size of an adult’s. But after just three months, your baby’s brain is 55% the size of an adult brain.

Your breast milk contains many different kinds of carbs, mostly in the form of sugar:

  • Lactose, the main carbohydrate in breast milk, is also known as milk sugar. This sugar is essential for the development of your baby’s nervous system.
  • Oligosaccharides help your breastfed baby grow healthy bacteria in his stomach, helping him properly digest the many nutrients in your breast milk. 

#3 Proteins 

Your breast milk is your child’s own personal protein shake! Proteins are the body’s building materials, the essential molecule for big projects from constructing bones and tissue to the framework for your child’s teeny tiny cells. 

One cup of human breast milk has about 2.5 grams of protein—a little less than a strip of bacon.  

#4 Lipids 

While lipids (otherwise known as fats) make up only 4% of your breast milk, these molecules have important work to do in your baby’s body. More than 50% of calories in breast milk are derived from lipids. Calories are an important source of energy for your child, powering her amazing baby growth spurts. 

Fat also helps your baby gain healthy weight. Fat stores energy for more growth spurts down the road, when that adorable baby chubbiness turns into the quick limbs of toddlers. 

Additionally, fatty acids like omega-3s help cognitive development, reduce the risk of becoming asthmatic, and promote brain growth. 

To learn more about “how many calories does a baby need”, visit our blog here. 

Micronutrients in Breast milk 

When it comes to breast milk, the small stuff is just as vital to your child’s health as the big stuff. Micronutrients in your breast milk perform myriad functions in your baby’s body. 


No need for chewable vitamins for your little one, your breast milk is full of these important nutrients. Vitamins are organic compounds – compounds that are naturally derived from living matter like plants or animals—that your body uses to help your systems operate smoothly. You get these vitamins from food, and your baby gets them from breast milk.

Your breast milk contains:

  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K
  • Vitamin C
  • A whole host of B vitamins including:
    • Vitamin B6
    • Vitamin B12
    • Thiamin (B1)
    • Riboflavin (B2)
    • Niacin (B3)
    • Pantothenic Acid (B5)
  • Folate

A healthy diet will guarantee that your breast milk is rich in these essential nutrients. But your doctor might prescribe additional vitamin supplements.

Vitamin D is a key element to your child’s development and it can be absorbed through food and sunlight—there’s a reason they call vitamin D the sunshine vitamin. Sunlight triggers the body to start making its own vitamin D. Because human babies are still developing melanocytes—the cells that help protect your child from the harmful aspects of the sun’s rays—your child may need additional vitamin D in liquid vitamin form.


Minerals work similarly to vitamins; the only difference is they are inorganic. That means they are elements that don’t come from living organisms like plants or animals, but instead are derived from the earth. Plants absorb minerals from soil and water, incorporating them into the plant’s chemical composition. From there, animals (like humans) eat and absorb the minerals into our bodies. 

Much like vitamins, minerals help your body and your baby’s body thrive. You’re probably familiar with minerals like iron, zinc, calcium, and more.

You might be wondering, is there iron in breast milk? Definitely! And a whole lot of other minerals like:

  • Zinc
  • Calcium
  • Sodium
  • Chloride
  • Magnesium
  • Selenium

If you’re worried about dairy intolerance in your baby, visit our blog here.

Bioactive Compounds 

One of the main differences between baby formula ingredients and breast milk are bioactive compounds. Bioactive compounds are organic substances that actively affect a person’s body. Think of it this way—vitamins and minerals are like building material for your body. Bioactive compounds are the contractors, carpenters, electricians, and interior designers. When they step onto the scene, they get to work.

Bioactive compounds that work within your child’s body to promote healthy growth and protect him from bacterial invaders. 

Immunoglobulins (Antibodies) 

Through your breast milk, you can give your daughter her own private microscopic army of antibodies to fight against illness. Antibodies are a special kind of protein that are designed to actively hunt down viruses in your child’s body and can help prevent:

  • Colds
  • Ear infections
  • Diarrhea
  • Vomiting

One antibody in particular, Secretory Immunoglobulin A (or IgA) helps prevent germs from entering your child’s body and bloodstream by acting as a sealant. IgA coats the baby’s lungs and intestines to help keep her infection-free. 


Hormones are the body’s chemical messengers. They zip around through blood, tissue, and organs and to tell the body to function well. Hormones impact several important functions like sleep, feelings of hunger, and growth. The hormones present in your breast milk help your baby’s brain send growth signals to the body, manage your child’s blood pressure, and maintain a healthy metabolism.

Thanks, Mom! 

Here are just a few hormones present in your breast milk:

  • Thyroid hormones – While thyroid hormones affect almost every part of the body, their most important function is helping your baby’s tummy break down food and turn it into energy. Thyroid hormones are also key to promoting proper growth and development in your child.
  • Epidermal Growth Factor (EGF) – This hormone stimulates cell growth for your baby’s digestive tract, blood, and saliva.
  • Beta-Endorphins – We all know that childbirth can be stressful for the parents to say the least, but it can also be hard on your child, too. Beta-Endorphins are the body’s natural painkillers. Scientists have theorized this helps babies destress after the craziness of childbirth.

    In fact, researchers discovered higher amounts of beta-endorphins in the breast milk of women who have a normal vaginal delivery, a premature baby, or women who decided not to get an epidural during childbirth.
  • Erythropoietin (EPO) – This hormone signals your baby’s body to produce red blood cells. Red blood cells transport oxygen from your baby’s breath to the body’s tissues.


There’s no doubt about it, your milk is full of good stuff for your child. But how does his body extract all the nutrients from the milk? With the help of enzymes.

Enzymes are bioactive proteins that accelerate chemical reactions in the body. Specifically, your breast milk enzymes help your child’s body break down the milk into more easily digestible chunks so your baby can put those nutrients to use.

Spill the Secrets of Your Child’s Nutritional Profile with SneakPeek Traits 

Breast milk certainly does your baby’s body good. But as wonderful as breast milk is for your child, it’s just the start of your child’s journey to a healthy, nutrient-rich life.

Take the first step of that journey together with SneakPeek.

SneakPeek Traits lets you discover your child’s unique nutritional profile as predicted by her DNA, so you can ensure she gets the vitamins she needs to feel her best. SneakPeek Traits can tell you if your child may need more of certain key vitamins like:

  • Vitamin E
  • Vitamin A
  • Vitamin D
  • B vitamins
  • Folate
  • And more!

Learn more about your child’s genetic nutritional needs with SneakPeek today! 



American Pregnancy Association. What’s in Breast Milk? https://americanpregnancy.org/first-year-of-life/whats-in-breastmilk-71018/

Nutrients. Review of Infant Feeding: Key Features of Breast Milk and Infant Formula. https://www.mdpi.com/2072-6643/8/5/279

Sutter Health. Breast Milk Production. https://www.sutterhealth.org/health/newborns/breast-milk-production#

VeryWell Family. The Process of Making Breast Milk. https://www.verywellfamily.com/how-the-body-makes-breast-milk-4153170

Very Well Family. The Vitamins in Breast Milk and Your Baby’s Needs. https://www.verywellfamily.com/the-vitamins-in-breast-milk-3964175

VeryWell Family. The Composition of Breast Milk. https://www.verywellfamily.com/whats-in-breast-milk-4047820

U.S. Geological Survey. The Water in You: Water and the Human Body. https://www.usgs.gov/special-topic/water-science-school/science/water-you-water-and-human-body?qt-science_center_objects=0#qt-science_center_objects

Rehydration Project. Exclusive Breastfeeding: The Only Water Source Young Infants Need

Frequently Asked Questions (FAQ). https://rehydrate.org/breastfeed/faq-exclusive-breastfeeding.htm

VeryWell Health Family. Overview of Hormones in Breast Milk. https://www.verywellfamily.com/hormones-in-breast-milk-p2-3984343

International Breastfeeding Journal. Study protocol: An investigation of mother-infant signalling during breastfeeding using a randomised trial to test the effectiveness of breastfeeding relaxation therapy on maternal psychological state, breast milk production and infant behaviour and growth. https://www.verywellfamily.com/hormones-in-breast-milk-p2-3984343

Mayo Clinic. Healthy Lifestyle: Infant and Toddler Health. https://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/expert-answers/vitamin-d-for-babies/faq-20058161

Live Science. Babies’ Amazing Brain Growth Revealed in New Map. https://www.livescience.com/47298-babies-amazing-brain-growth.html

SneakPeek aims to provide the most accurate and up-to-date information to help our readers make informed decisions regarding their health before, during, and after pregnancy. This article was written based upon trusted scientific research studies and/or articles. Credible information sources for this article are cited and hyperlinked.

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