What’s in Breastmilk?

(c) Diane Dehler. Used with Permission

You may have heard women in your community, maybe your own mother or grandmother, talk about breastfeeding their babies. Many people say that nursing a baby is the “best” choice for mothers and that all mothers should breastfeed their babies. Have you ever wondered what is in a mother’s milk that makes it so different from formula? Unlike formula, your milk is species-specific (made for humans) and provides all of the nutrients needed for your baby to grow healthy and strong.

Milk is made up of many parts. There are the non-nutritive elements, some of them so small even the best laboratory is unable to reproduce them. These bioactive components do more than offer food: they are busy protecting your baby’s urinary tract from infection and keeping your infant’s gut free of harmful bacteria and viruses. There is speculation that the reason a mother’s milk is so full of antibodies and immunological components is that when a baby is born, its own defense system is very immature. Your child’s immune system will not be fully mature until he is about 4 years old, so your baby is born relatively helpless and very vulnerable to disease. When you are breastfeeding, you protect your baby by coating his intestines and other parts of his immature digestive system with specialized, protective proteins, and the immune factors of breastmilk work in his blood stream as well. Your milk provides a strong barrier to unwanted germs.

According to the insightful work of Dr. Ann Prentice in 1996, the list of non-nutritional factors include the following elements:

“Antimicrobial factors: secretory IgA, IgM, IgG. lactoferrin, lysozyme, component C#, leukocytes, Bifidus factor, lipids and fatty acids, antiviral mucins, GAGs, oligosaccharides.”

  • Lactoferrin works as an iron carrier which is also antimicrobial, particularly against E.coli bacteria.
  • Lysozyme is bacterocidal (kills bacteria) and anti-inflammatory, and as you continue to breastfeed, the levels slowly rise and reach their highest point around 6 months. Nurse your baby for as long as you want. Your milk will help protect him from disease for as long as you breastfeed.
  • sIgA, IgG, and IgM work to provide an extension of the mother’s immune system to the baby. The maternal antibodies are expressed in breastmilk in order to give immunity (protection) to specific illnesses (antigens) in the environment. Keeping the mother and baby together after birth gives the mother more opportunities to build antibodies to any bacteria in their shared environment. If this topic is particularly interesting to you, here is another article about the enteromammary host immune system.
  • Long-chain polyunsaturated fatty acids (lc-pufa), in particular DHA and AA, are associated with eyesight and cognitive thought processes (thinking). For these two factors, the content in breastmilk is related to the mother’s diet.

(Listed in Table 1) Other examples of the non-nutritional components of breastmilk of Ann Prentice’s paper:

“Cytokines/anti-inflammatory: tumor necrosis factor, interleukins, interferon-γ, prostaglandins, antioxidants, α-1 antitrypsin, α-1 antichymotrypsin.

Hormones: feedback inhibitor (FIL), insulin, cortisol, prolactin, thyroid hormone, corticosteroids, ACTH, oxytocin, calcitonin, PHrP, erythropoietin.

Digestive enzymes/others: BSS-esterase, BSS-lipase, amylase, lipoprotein-lipase, casomorphin, β sleep peptides, nucleotides, DNA, RNA.”

You might notice that some of the components we have listed in this article are repeated in more than one category: they serve more than one purpose. In fact, some of these factors have nutritional purposes after they have completed their antimicrobial work and been digested or absorbed. They relate to each other and to the baby’s body. As the milk is digested, more bioactive factors are made, and they in turn have new effects on the baby. You could view it as a connected circle between the mother, the baby, and the milk.

Here are a few more details about the some of the major players in milk:

  • Amylase is an enzyme that is necessary for the body to break down starches in foods. It makes digesting breastmilk much easier for your baby.
  • BSSL (Lipase for short) is an enzyme the body needs to break down fats and is also helpful for your baby.
  • The platelet-activating factor helps to speed up any needed healing of the mother’s nipple and also in the gut of the infant.
  • Casein makes if difficult for microbes to attach to the mucosal  lining in your baby’s body. Those linings cover the inside of the lungs, the digestive tract, the nose–all ports of entry are covered by mucosa.
  • Oligosaccharides work as major protectors against germs. They have parts called ligands that fool the bacteria and viruses into thinking they are part of the baby; the bacteria and viruses attach to the oligosaccharides instead, and they are then flushed all the way out of the baby’s body.

There are certain proteins in milk that serve protective functions:

  • β-casein
  • Whey: α-lactalbumin: HAMLET (Human α-lactalbumin Made Lethal to Tumor cells), lactoferrin, immunoglobulins, lysozyme, and serum albumin

There are carbohydrates to provide the calories needed for your baby’s growth:

  • Lactose
  • Lactose-N-tetraose

There are fats that support calorie storage for growth spurts and are essential for brain-growth and development of eyesight:

  • Triglycerides (the primary fat in breastmilk)
  • Oleic acid
  • Palmitic acid
  • Arachidonic acid (AA)
  • Docosahexaenoic acid (DHA)

There are cells that have special jobs keeping your baby healthy:

  • Leukocytes (white blood cells): Phagocytes, Basophils, Neutrophils, Eoisinophils, and Macrophages
  • Lymphocytes: T cells and B cells
  • Stem cells

There are growth factors:

  • Cortisol
  • Insulin-like
  • Thyroxine
  • Cholecystokinin (CCK)
  • Epidermal
  • Nerve
  • Transforming
  • Taurine
  • Polyamines

* The following hormone sections (vitamin, mineral, transporter, and cytokine) would be incomplete were it not for the work of Cecily Heslett, Sherri Hedberg, and Haley Rumble. We relied heavily on their work, and this section should be credited to them with only minor additions by us.

There are hormones:

  • Oxytocin
  • Prolactin
  • Feedback inhibitor (FIL)
  • Insulin
  • Cortisol
  • Corticosteroids
  • ACTH
  • Calcitonin
  • PHrP
  • Erythropoietin
  • Triiodothyronine (T3)
  • Thyroid stimulating hormone (TSH)
  • Thyroid releasing hormone (TRH)
  • Thrombopoietin
  • Gonadotropin-releasing hormone (GnRH)
  • GRH
  • Leptin
  • Ghrelin

There are vitamins:

  • Vitamin A
  • Vitamin C
  • Vitamin B1
  • Vitamin B2
  • Vitamin D
  • Vitamin E
  • Vitamin K
  • Beta carotene
  • α-Tocopherol
  • Thiamine
  • Riboflavin
  • Niacin
  • Folic acid
  • Pantothenic acid
  • Biotin

The minerals:

  • Calcium
  • Phosphorus
  • Sodium
  • Potassium
  • Chlorine
  • Zinc
  • Magnesium
  • Iron
  • Copper
  • Manganese
  • Iodine
  • Selenium
  • Choline
  • Sulphur
  • Chromium
  • Cobalt
  • Fluorine

There are cytokines/anti-inflammatory elements:

  • Antioxidants
  • α-1 antitrypsin
  • α-1 antichymotrypsin.
  • interleukin-1β (IL-1β)
  • IL-2
  • IL-4
  • IL-6
  • IL-8
  • IL-10
  • Granulocyte-colony stimulating factor (G-CSF)
  • Macrophage-colony stimulating factor (M-CSF)
  • Platelet-derived growth factors (PDGF)
  • Vascular endothelial growth factor (VEGF)
  • Hepatocyte growth factor-α (HGF-α)
  • HGF-β
  • Tumor necrosis factor-α
  • Interferon-γ
  • Epithelial growth factor (EGF)
  • Transforming growth factor-α (TGF-α)
  • TGF-β1
  • TGF-β2
  • Insulin-like growth factor-I (IGF-I)
  • Insulin-like growth factor- II
  • Nerve growth factor (NGF)
  • Erythropoietin

There are also transporters:

  • Lactoferrin (Fe)
  • folate binder
  • Cobalamin binder
  • IGF binder
  • Thyroxine binder
  • Corticosteriod binder.

There are many good things in a mother’s milk that are still unknown, and the topic is still being explored. The effects of breastfeeding your baby last a long time–far into his adulthood, and it may influence the health of his children, grandchildren, and later generations. Even if you are smoking or are an occasional light drinker, your baby still needs your milk. The next time someone tells you that formula is easier, you can show them this article, and they can compare the ingredients on the back of a formula can to this list. Breastfeeding is the natural choice, and breastfeeding your baby results in better health for both of you.


Prentice, A. (1996) Constituents of human milk,. Food and Nutrition Bulletin, (The United Nations University Press), 17(4)

Heslett, C., Hedberg, S. & Rumble, H. Breastmilk poster. Douglas College, New Westminster, BC, Canada.

Riordan, J. & Wombach, K. (2010), Breastfeeding and Human Lactation, 4th edition. Jones and Barlett Publishers.

Lucas, A., Gibbs, J. & Baum, J.D. (1977), What’s in breastmilk. Lancet, 8019:1011-2

Garofalo, R. (2010), Cytokines in human milk. Journal of Pediatrics. 152 (2 suppl): s36-40

Walker, A. (2010), Breastmilk as the gold standard of protective nutrients. Journal of Pediatrics, 152 (2 suppl): s3-7

Cregan, M.D. et al. (2007), Identification of nestin-positive putative mammary stem cells in human breastmilk. Cell Tissue Res. 329(1):129-36

Lehti, K.K. (1989), Iron, folic acid and zinc intakes and status of low socio-economic pregnant and lactation amazonian women. Europian Journal of Clinical Nutrition. 43(8); 505-13

(c) 2015. Serena Meyer RN, IBCLC

You can find Serena at https://www.bayareabreastfeedingsupport.com/

Updated 5/2019

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3 Responses to What’s in Breastmilk?

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