The Composition of Breast Milk

Explore the Nutritional Benefits and Components of Breast Milk

Latino, hispanic, mother feeding newborn baby girl

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Human breast milk is recognized by health organizations around the world as an ideal source of nutrition to support early life. A diet of exclusively breast milk is recommended for the first 6 months of life followed by the addition of solid foods plus breastmilk for up to 2 years of age. What's in breast milk that makes it such a highly recommended choice?

Breast Milk vs. Infant Formula

Breast milk is produced by a woman's body specifically to meet her child's nutritional needs. It provides everything a baby's body requires for proper growth and development, changing in response to the baby's needs. Not only is breast milk a complete source of nutrition and hydration, but it also helps protect babies from getting sick through antibodies that pass from mother to baby through the milk.

Breast milk is composed of hundreds of distinct bioactive molecules, some of which are not yet fully understood by scientists. Although infant formula also provides complete nutrition, it doesn't fully replicate the immune benefits of breast milk.

Nonetheless, infant formula is a safe and acceptable alternative to breast milk. For parents who cannot offer breast milk or who prefer not to breastfeed, infant formula is a suitable option. Ultimately, ensuring that an infant receives adequate nutrition, whether from breast milk or formula, is the most important thing.

Macronutrient Composition

Breast milk is primarily composed of water, carbohydrates, lipids, and proteins. Each of these nutrients plays a role in contributing to infant growth and development.


Human breast milk is made up of about 90% water. The human body depends on water to function. Water maintains hydration, helps regulate body temperature, lubricates joints, and protects organs. Luckily, breast milk alone provides all of the water required by young babies for survival.


Carbohydrates are a preferred energy source for the brain. The main carbohydrate in breast milk is milk sugar, known as lactose. Human milk contains more lactose than cow's milk.

Other carbohydrates found in breast milk (such as oligosaccharides) promote healthy bacteria in your baby's intestines. These bacteria protect your baby's gut and can help fight off diseases like infant diarrhea.

Lipids (Fats)

Lipids may only make up about 4% of breast milk, but they provide over half of the calories that your baby receives from it. Lipids are a major source of energy, cholesterol, and essential fatty acids such as DHA. These nutrients are necessary for the development of your baby's brain, nervous system, and vision.

All breastfeeding mothers should take a DHA supplement. If you are vegetarian or vegan, you may also need a B12 supplement.

The high-calorie content of lipids in breast milk is also responsible for the baby's healthy weight gain. Breast milk should naturally contain all the lipids your baby needs to grow for the first 6 months of life.


Proteins build, strengthen, and repair the body's tissue. They are also needed to make hormones, enzymes, and antibodies. The protein in breast milk is easy for babies to digest and these proteins are essential throughout every stage of the lifecycle for humans to survive.

Lactoferrin is a form of protein in breast milk that moves iron through your baby's body. It also helps protect your newborn's intestines from infections.  

Bioactive Components

There are several elements of breast milk that cannot be found in formula. These unique substances are passed from the mother.

Immunoglobulins (Antibodies)

Immunoglobulins are antibodies that fight off illness and disease. Because of these natural immune substances, breast milk can almost be thought of as a baby's first vaccine. The properties of breast milk help protect against the common cold, ear infections, vomiting, diarrhea, and other potentially dangerous infections.​

The primary antibody in breast milk is Secretory Immunoglobulin A (IgA). IgA coats the baby's lungs and intestines, sealing them to prevent germs from entering the body and bloodstream. Babies who are born premature and those who will be attending daycare right away are especially poised to benefit from the added immune support that breast milk can provide.


Hormones have many jobs in the human body. They influence growth and development, metabolism, stress and pain responses, and blood pressure regulation. Hormones involved in milk production include prolactin, thyroid hormones, and growth factors.

Scientists are still researching which hormones are transferred into breast milk (such as leptin) to learn more about how they impact a baby's health.


Several key enzymes are found in human breast milk. Some aid digestion by breaking down fats or proteins, while others provide immune support.

Many of the enzymes in human breast milk have unknown functions. While we may not fully understand what all of these enzymes do, there's a good chance they play beneficial roles in infant development.


Breast milk contains the vitamins and minerals needed to support young babies. Formulas also contain many of these vital micronutrients.


Vitamins support healthy bones, eyes, and skin. They are necessary to prevent diseases of malnutrition, such as scurvy and rickets. Breast milk typically contains all the vitamins needed to support your baby's health as they grow. However, the amount of vitamin D, folate, or vitamin B6 in your body may be lower if you follow certain dietary restrictions.

Talk to your doctor and pediatrician to find out if there are any vitamin supplements you should take to support breastfeeding. It's often recommended for women to continue taking prenatal vitamins until they finish breastfeeding.


Like vitamins, breast milk is also full of minerals that your baby's body needs to grow healthy and strong. These include iron, zinc, calcium, sodium, chloride, magnesium, and selenium. Minerals are used to build strong bones, produce red blood cells, and promote proper muscle and nerve function.

A Word From Verywell

Breast milk is an excellent source of nutrients for babies. While infant formulas are a safe and healthy alternative to breast milk, they are not exactly the same in terms of the bioactive properties that breast milk can offer.

Talk to your doctor, pediatrician, and family about whether breast milk is an accessible option for you and your baby. Only you can decide what is right for your child. As long as the baby is adequately fed, with breast milk or formula or both, parents should feel good about the nutrition they are providing to their little ones.

15 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • American Academy of Pediatrics. New Mother’s Guide to Breastfeeding. New York, NY: Bantam Books; 2011.

  • Lawrence RA, Lawrence RM. Breastfeeding: A Guide For The Medical Profession. 8th ed. Philadelphia, PA: Elsevier Health Sciences; 2015.

  • Riordan J, and Wambach K. Breastfeeding and Human Lactation. 5th ed. Sudbury, MA: Jones and Bartlett Learning; 2015.

By Donna Murray, RN, BSN
Donna Murray, RN, BSN has a Bachelor of Science in Nursing from Rutgers University and is a current member of Sigma Theta Tau, the Honor Society of Nursing.