Introduction

Breastfeeding appears to be a simple process. It’s just a mom feeding her baby, right? But breastfeeding is so much more! Breastfeeding is more than just the flow of breastmilk. It encompasses a set of complex processes that flow between a mother and her child. A surge of hormones in a mothers brain bonds her closer to her baby during breastfeeding, while also triggering a cascade of physiologic processes that lead to the nourishment of her baby. It is truly a unique and special experience. 

The World Health Organization (WHO) and the American Academy of Pediatrics (AAP) recommends breastfeeding for at least the first 6 months of life to give the most benefit to an infant.⁸ From the 2018 CDC National Immunization Survey, it was shown that about 83.9% of infants are breastfed in general, which includes mothers who exclusively breastfeed or combo feed. 46.3% of infants are exclusively breastfed for 3 months and 25.8% for 6 months.⁸ This shows that mothers are likely to breastfeed at some point after delivery, but it is not often that mothers exclusively breastfeed for longer than 6 months. However, about 35% are breastfed (either exclusively or combo fed) at 12 months. 

No matter if a mother breastfeeds her infant for 6 months or 2 years, there are breastfeeding benefits for any amount of time. We are going to explore some of those in this post. You might even be surprised by what you learn!

Breast Tissue Anatomy

To understand how these complex processes work together, it is important to first look at the breast anatomy. 

• Breast glands
  • Multiple lobes, about 15-20 on each breast, which are then composed of small lobules. Lobules are made up of small alveoli. 
  • Where breast milk is produced
• Mammary ducts
  • Transfer and excrete breast milk
  • Lined by myoepithelial cells that contract and release milk through the ducts, especially during the let-down response (see below)
• Nipple
  • Contain small pores that allow for milk to exit from the lactiferous ducts
  • Montgomery glands
    • Small nodules or bumps on the nipple that secretes oil to cleanse the nipple and and prevent dryness  

Hormonal Involvement

There are two main hormones that trigger the cascade of events for milk ejection and flow: oxytocin and prolactin. As an infant begins to suckle, prolactin is released from the anterior pituitary gland and stimulates the myoepithelial cells (see the above diagram in the anatomy section) in the breast ducts to produce milk. Interestingly, prolactin levels are the highest at night, which shows that it is essential to feed at night to support milk production and supply. Oxytocin, also known as the “love hormone,” is also secreted from the pituitary gland, but the posterior side. It acts on myoepithelial surrounding the alveoli in our breasts to cause contraction of these cells, and therefore, a milk ejection reflex. The milk ejection reflex is known as a let-down. You probably have heard this term before. Usually a let-down occurs a few minutes or so after a baby begins to nurse. Oxytocin is stimulated by suckling, but also by the sweet hormonal response when a mother thinks or interacts with her baby.¹⁰ 

So, if you’re breastfeeding or in late-pregnancy and you have noticed that you’ve leaked after thinking about your cute baby don’t feel alone. It happens to all of us! 

Another note on prolactin: Prolactin also suppresses GnRH and FSH (hormones that lead to the production of progesterone and estrogen in the ovaries, which dictate the entire process of a woman’s cycles such as her period and ovulation). Therefore, periods are halted while breastfeeding. It serves as a temporary birth control. 

Another note on Oxytocin: During skin-to-skin contact while breastfeeding, an infant is able to better regulate their temperature and feel calm/comforted after its release.⁶ Specifically, when a baby beings to nurse, a mother’s breasts release heat which leads to the vasodilation (expansion of the blood vessels) in the baby’s skin and an increase in the infant’s body temperature.¹²

A few other hormones/proteins also play a role: 

• Parathyroid hormone-related peptide (PTHrP): Triggers the body to release calcium from stores in the body to be used for milk production
• Feedback inhibitor of lactation (FIL): The FIL is located in the breast milk ducts. When the ducts are full of milk, the FIL communicates with the brain to tell the brain that no more milk needs to be produced. When a baby nurses, the FIL is removed, and therefore, more milk is produced. Pretty cool!

Maturation of breast milk

• Colostrum → Transitional Milk → Mature milk
  • Colostrum → thick, yellow milk that contains immune cells, antibodies, and other proteins 
  • Transitional Milk → a mixture of colostrum and mature milk 
  • Mature milk → milk that continues to nourish the infant from two weeks onward, however this milk is adaptable, dynamic as the infant grows and has different nutrition and immunologic needs.¹⁰
• Of mature milk, there are two parts of the milk, the foremilk and the hindmilk. As hinted by their names, the foremilk comes first and the hindmilk comes last. Foremilk has higher contents of water, while hindmilk has higher fat content. This highlights the balance between hydration of the infant, while also giving them nutrients.
  • Foremilk → thinner, more watery. 
  • Hindmilk → creamery, higher fat content

While nursing, infants only intake about 70% of the available milk stored in the mother’s breasts. This highlights that the amount of milk a mother produces and stores, and the amount of milk an infant intakes during a session can change as the infant grows. In addition, the time nursing changes throughout infancy. This is because an infant can intake more and become more efficient as their development matures.¹⁰ An infant may initially nurse 20-40 minutes total in the newborn phase, and then feed between 8-15 minutes as a 7 month old. 

Breast Milk Is Alive

The components of breast milk are designed to sustain the infant for the first year or so of life. The nutrients and immunological contents are an essential part of infant development and immune protection.¹

1. Proteins
   1. Whey and casein
      1. Whey makes up the vast majority, compared to casein in the beginning, but towards 6 months postpartum they are more equal.
      2. Whey is easier for an infant to digest rather than casein, which is higher in cow’s milk
      3. Each made up a large complex. These complexes contain other proteins:
         1. Components of immunity
            1. IgA: This is an immunoglobulin or antibody. It helps recognize pathogens to trigger an immune system response, and protect the infant’s gut from infections. 
            2. Cytokines: These are small proteins that help initiate an immune response and inflammation 
            3. White blood cells: WBCs are the primary immune cells. WBCs encompass neutrophils, lymphocytes (B, T cells, natural killer cells), monocytes, eosinophils, and basophils. 
         2. Hormones
            1. Epidermal Growth Factor (EGF) is a hormone that helps support the growth of the lining of the intestines and heal after injury (i.e. from harmful bacteria). It may also play a role in preventing necrotizing enterocolitis (NEC) which is the death of an infant’s intestine.¹³
         3. Glutamine
            1. An amino acid that is present in large quantities in breast milk that helps facilitate hormones in the brain and the gut communicate, which is necessary for a baby’s proper growth and digestion. 
         4. Enzymes
            1. Help eradicate dangerous bacteria that could harm the baby’s gut 
         5. Lactoferrin: the “miracle molecule”¹¹
            1. Like certain enzymes in milk, lactoferrin is an excellent defender against dangerous pathogens. 
            2. In this one article, see reference 11, it is known as the “miracle molecule.” Why? It may play a role as a powerful antioxidant (reducing what is called oxidative stress that can cause DNA damage and cell death), antibacterial, and anti-inflammatory. 
         6. Alpha-lacalbumin
            1. Helps synthesize lactose, with the absorption of vitamins, and digest fats 

2. Fat
   1. 3-7% of breastmilk
   2. Varies upon maternal factors
   3. Some building block components of fat, such as fatty acids, help to make DHA (as you might have seen in your prenatal) which is essential for infant brain development and nerve function.
3. Carbohydrates
   1. Lactose content is about 7%, and serves as a building block for oligosaccharides and helps the absorbs of other vitamins and minerals such as calcium
   2. Human Milk Oligosaccharides (HMOs)¹⁴
      1. A prebiotic (food for healthy gut bacteria)
         1. As the infant grows, the types of HMOs change, as the microbiome in the infant gut changes.
      2. Greatest amounts in colostrum
      3. A derivative of lactose 
      4. Maternal diet can affect types of HMOs
      5. Linger in the gut and trigger an immune response against pathogens 
      6. Prevent the growth of harmful bacteria and viruses (RSV, influenza, etc.)
4. Water
   1. Water makes up the vast majority of breastmilk, reaching about 87%¹⁰
5. Vitamins
   1. Vitamin D & K are present in low amounts 
   2. Iron, zinc, magnesium, calcium, and more! Think of your prenatal vitamins, but more. 
6. Bacteria
   1. Mostly Bifidobacterium species, but also Lactobacillus, Staphylococcus, and Streptococcus.¹⁴

As you can see, breast milk is not just fat and water. It is so much more! It is very important that a mother who is breastfeeding intake healthy fats, as well as carbohydrates. Yes, it is essential to eat these things! Your baby needs them. That does not mean to jump to eating sweets or fast food. But foods that nourish you = nourishment to your baby. A balance of proteins (meats, fish, dairy), carbohydrates (dairy, fruits), and healthy fats (oils, meats, eggs, fish, nuts) are essential! If you’re breastfeeding, this is not the time to diet. It’s a great time to create a good nutrition store. If you’re breastfeeding, this book (although catered to pregnancy) is a great one to read on nutrition. 

The Gut-Breast Axis

The breast-to-infant gut axis describes the transfer of maternal nutrients and living organisms to assist with growth, protect, and colonize the gut of an infant. 

This can get a little complex, but I promise this is cool. Hang in there. 

There are multiple components that travel from mom to baby. Feel free to refer back to the “Breast milk is alive” section which highlights the components of breast milk. We will discuss a few here: 

• Bacteria: Maternal immune cells, called dendritic cells, capture bacteria from a mother’s gut. Dendritic cells re-enter a mother’s circulation to the breast mammary gland tissue. There are more dendritic cells in the breast tissues during late pregnancy and during lactation. Dendritic cells are released into breast milk. Therefore, so are bacteria. These bacteria, mostly Bifidobacterium, Lactobacillus, and Streptococcus, travel to the infant’s gut and colonize it. These bacteria, as we explained above, are beneficial bacteria. They help protect the infant’s gut from harmful bacteria and other pathogens, such as viruses. This process is called the entero-mammary pathway.¹⁵ The retrograde flow of an infant’s saliva and oral bacteria (backwash) to a mother’s breast may also help support immune regulation between mom and baby.^20,21 
  • Human Milk Oligosaccharides (HMOs), as described above in the carbohydrates section, change through this dynamic flow between mother and baby. HMOs produced by the mother help the growth of these healthy bacteria in the infant, which are commonly found in OTC probiotics. In addition, these HMOs prevent the growth of harmful bacteria in the infant, such as E. coli which cannot use HMOs as energy fuel. Formula feeding leads to a more diverse gut microbiome, similar to that of adults. However, this can increase the amounts of harmful bacteria, which can have negative effects if the harmful bacteria become more prominent than the beneficial ones.¹⁴
• Immune cells: Breast milk contains immune cells (i.e. dendritic cells), antibodies, and other components of the immune system (i.e. cytokines). The tissue within the mammary glands are home to these agents in the immune system, and are thought to be structurally similar to that of our gut. It is not exactly known how these immune cells travel to the mammary glands during late pregnancy and lactation, but some of them travel through the entero-mammary pathway (gut to breast). They may also travel after a mother’s exposure to harmful bacteria in the gut. These immune cells in breast tissues become a part of a mother’s breast milk.
  • Antibodies present in breast milk can directly affect an infant’s allergy to foods. For example, a mother’s exposure to cow’s milk increases her IgA antibodies in breastmilk, which can play a role in prevention of a cow’s milk allergy. However, more research is needed on this concept.^17,19 
• Nutrients: From a mother’s diet and stores in her body, macronutrients (protein, carbs, fats), micronutrients (vitamins and minerals), and water travel through the bloodstream and are used to compose breast milk. These nutrients fuel an infant, supporting their growth and development. Therefore, it is essential that a mother maintain a well-balanced diet in order to have stores of all the necessary vitamins and minerals.^17,19

• Others:
  • Our cells produce small vesicles that help transport other molecules to other cells. These vesicles can contain fats, proteins, RNA, and miMRNAs. MiMRNAs or microMRNAs do not code for specific proteins but rather help regulate the expression of other genes and their expressions of proteins. Okay, but why do these matter? Y’all this is pretty cool. These vesicles containing these nutrients and gene-regulating components are present in breastmilk. The vesicles act as tiny transport vessels and protect their contents from being digested by the infant so they can be delivered to their gut without disruption. Once they reach the infant gut, they are released into the intestinal cells. These components may (and I say may because this is a newer concept being studied) help the infant’s gut develop. The microMRNAs can help with development and immune regulation.¹⁷
• Maternal stem cells travel to the infant and stay with the infant, and help with their growth and immune system development. This is known as microchimerism. Similarly in pregnancy, a mother and fetus pass cells through the placenta to each other and provide benefits to both. It is still a new topic that is being researched, but it is very cool to think about.^17,18 

Okay, so you made it through a complex explanation of how a mother’s nutrition and microbiome affect their infant (if you want to read more I would recommend looking into reference 17 and its images). What else can breastmilk do for a baby? 

Other Benefits

Infant 

• Reduction of:
  • SIDS, by up to 60% if a child is exclusively breastfed for the first 6 months of life
  • Gastrointestinal (i.e., stomach bug) or pulmonary infections (i.e., pneumonia)
  • Allergies 
  • Ear infections 
  • Mortality 
  • Likelihood of malocclusion (misalignment between the upper and lower teeth)⁵
  • It is worth noting from the AAP Breastfeeding Guidelines that mothers who are in the Non-Hispanic Black population who have “suboptimal breastfeeding” can have an increased risk of ear infections, inflammation and death of the infant colon (necrotizing enterocolitis), and child death. These risks are significant. Any breastfeeding in this population can lead to a 17% reduction in infant mortality.⁸
• Prevention of overfeeding that can occur with bottle feeding with formula or expressed breastmilk (pumping), which can reduce the risk of childhood obesity and diabetes as an adult⁴
• Breastfed infants tend to have increased amounts of bilirubin. Bilirubin is a waste product after older red blood cells (RBCs) have been processed by the body. When levels of bilirubin are increased, this is called hyperbilirubinemia. Breastfeeding less than 7 times per day is associated with higher bilirubin levels, while 9 or more times a day is associated with less amounts of bilirubin.⁸ Hyperbilirubinemia can cause yellow of the skin (jaundice). In most cases this is combated with adequate infant nutrition support.⁹

Mother 

• Positive mental health outcomes 
• Supports natural birth spacing, because nursing an infant causes amenorrhea (aka no periods)⁴
• Reduction in risk of ovarian and breast cancers, as well as type 2 diabetes, cardiovascular diseases, and endometriosis^4,7

Please reference the American Academy of Pediatrics (AAP) Breastfeeding Guideline for specific risk reductions.⁸ 

What if my infant is not breastfed?

If you’re reading this article and thinking “my baby isn’t breastfed” or “my baby drinks formula,” don’t fear! 

If you exclusively pump and feed your baby breastmilk, they are still getting the benefits of breastmilk. The contents will be similar. However, the ability to help an infant temperature regulate, and provide biofeedback to the mother cannot occur by exclusively pumping.

If you formula feed, formula does provide the nutrients an infant needs. Many infants who are formula fed, especially those who are preterm, grow and develop without issues. However there are no bioactive components found in formula as in breast milk. 

Donor milk is available if breastfeeding is not an option. Most local hospitals have donor milk available if needed. 

Summary

The special bond between a mother and her baby during breastfeeding is an experience that is hard to put into words. It is nourishing, yet also a connecting and emotional experience from mom to baby. It is essential for infant nutrition, but involves complex communication from a mother’s gut and brain to the breast. To summarize, the breast is just the mediator between an infant and a mother’s gut microbiome and immune system. The flow of nutrients is dynamic and supportive for exactly what the infant needs. There is nothing like it!

Sometimes breastfeeding can feel overwhelming and daunting, especially as a first-time mom. Support is absolutely essential when it comes to breastfeeding. It has been shown that mothers who receive support during their breastfeeding journey are more likely to breastfeed for longer.² This makes total sense, as it can be hard at times! If you have questions about breastfeeding or need someone to cheer you on, we are here for you! We also recommend reaching out to a lactation consultant to answer any specific medical questions.

If you are interested in some products that can help you while breastfeeding, feel free to see our breastfeeding page.

Kind Regards,

The PA Sisters

Disclaimer: This post contains affiliate links. As Amazon Associates, we earn from qualifying purchases at no extra cost to you. The PA Sisters are licensed Physician Assistants in the state of Texas, but all content on this blog is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Product recommendations reflect our personal opinions only and do not establish a provider-patient relationship. Always consult your own licensed healthcare provider before purchasing or using any health-related product. Read our full Medical Disclaimer and Disclosure Policy.

References

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