Breastfeeding and the Microbiome

08/29/2019 | 8 min. read

Dr. Briana Sinatra

Dr. Briana Sinatra

One of the main benefits of breastfeeding that people may not know about is assisting with the establishment of a healthy microbiome. This has profound immunological benefits throughout a person's life, but that is not all! There are many benefits of breastfeeding that extend not only to baby’s short-term and long-term health, but to mom’s health as well!

Before I begin, I want to touch on something very important that shouldn't be overlooked. I know breastfeeding can be a source of pain, frustration, and guilt. As can many ideals of parenting that in reality are met with challenges, for a variety reasons. We put enough pressure on ourselves as parents, so this is not an article of shoulds or should haves. If you weren't breastfed as an infant or weren't able to breastfeed your own child, please, no remorse or guilt. All we can ask of ourselves is to do the best we can in the moment and have compassion for ourselves when our expectations or desires don’t align with the actual outcome. Thankfully, there are many ways to support the infant microbiome and our child's health. Breastfeeding is just one of them. 

Microbiome Development Begins at Birth

The infant microbiome is evolutionarily designed to be seeded (the process of receiving foundational microbes) in 4 main ways, through:

1. Vaginal delivery

One of the first places of microbial seeding for a vaginally delivered baby is through inoculation from their mother’s vaginal microflora as they pass through the birth canal.

The mom's flora enters the emerging baby through their:

  • eyes
  • ears
  • nose
  • mouth
  • skin

2. Skin-to-skin contact

After birth, a second important exposure for the infant microbiome is immediate skin-to-skin contact (SSC). For infants born via C-section, this can be an important first exposure in establishing a healthy microbiome. SSC is achieved by placing the baby directly on their mom’s bare chest immediately after delivery. If their mother is not available right away (e.g., is in recovery post C-section), this skin-to-skin contact can be made with their father, other parent, or family member. Even in the cases of C-section, and even if the infant isn't breastfed, this skin-to-skin contact alone provides numerous benefits for both the mom and baby.

3. Breastfeeding

A third route of microbial exposure important for infant microbiome development is through breastfeeding. The act of latching at the nipple, as well as drinking breast milk both introduce beneficial organisms to the baby. In fact, breast milk provides one of the largest microbial exposures. It has been found that a baby consuming around 800 mL/day of milk (commonly seen by 15 weeks of age) ingests between 100,000 to 10,000 000 CFU of beneficial bacteria a day!

Benefits of Breast Milk

Breast milk has beneficial probiotics that support a baby’s developing microbiome. Some bacterial strains transferred from mom to infant through the breast milk are:

  • Lactobacillus
  • Staphylococcus
  • Enterococcus
  • Bifidobacterium

After the introduction of all this bacteria into the infant’s gut, nature has a divine plan to help the bacteria grow. Breast milk is packed full of important insoluble, prebiotic fibers that are specifically designed to feed and proliferate the bacteria in the gut into a thriving community. These prebiotic fibers are called Human Milk Oligosaccharides (HMOs).

This is so important that the milk of mothers who deliver preterm infants (known to have immature guts and a higher risk of infection) has higher amounts of HMOs, as does early milk after delivery of a full-term infant compared to the milk of moms with older nursing infants.

Colostrum – the Liquid Gold

Colostrum is the first secretion produced from the breast postpartum. It often has a yellow, golden hue due to its carotenoid content. It is rich in immunologic factors and growth factors and relatively low in carbohydrates. This indicates that its primary function is immunological not nutritional. Hence the term liquid gold — even if you are not able to breastfeed, expressing this fluid and finger feeding it to your baby is tremendously beneficial for the baby’s gut and immune health.

Transitional Milk and Mature Milk

Once breastfeeding is established, around the 3rd day after delivery, transitional milk starts to be produced in the mom's breast. The transitional milk contains more nutrient components then colostrum but still maintains a relatively high amount of immunological and growth factors. It transitions over the next 2–3 weeks into mature milk which remains until breastfeeding is discontinued.

Immune-related Components of Breast Milk

Certain components of breast milk are important for passive protection against infections and immune-mediated diseases by modulating immunological development. This is partially achieved by aiding the growth and development of the enteral nervous system and the growth and repair of the intestinal lining by tightening gap junctions. These immune-related components of breast milk include:

  • white blood cells
  • stem cells
  • immunoglobulins (IgA)
  • cytokines
  • growth factors
  • hormones

Health Benefits of Breastfeeding

Research has suggested that breastfeeding's contribution to the infant microbiome may have a protective effect against several diseases. Breastfeeding has been shown to:

Improve infant health by lowering the risk of:

  • late-onset sepsis in preterm infants (bacteremia)
  • necrotizing enterocolitis
  • gastrointestinal tract infection and diarrhea
  • urinary tract infection
  • respiratory tract infections
  • otitis media
  • allergic disease
  • atopic dermatitis
  • asthma

Prevent health problems later in life by reducing the risk of:

  • inflammatory bowel disease
  • type 1 and type 2 diabetes
  • lymphoma, leukemia, and Hodgkin’s disease
  • childhood overweight and obesity

Improve mother’s health by:

  • decreasing postpartum bleeding and more rapid uterine involution
  • decreasing menstrual blood loss
  • increasing child spacing (lactational amenorrhea)
  • easing the return to pre-pregnancy weight
  • decreasing risk of breast and ovarian cancers

Important Nutritional Components of Breast Milk

At no other time than the first year of life do humans go through such rapid growth and development. It is amazing that nature provides exactly what is needed within breast milk to accomplish this. Breast milk even contains enzymes to help the baby digest the nutrients it contains.

Breast Milk Contains:

  1. Water

Not nutritional per se, but essential for life! Babies don't need additional water while they are nursing. They get all their hydration and nutritional needs met through breast milk for at least the first 6 months of life. That is why it is important for mom to drink plenty of water and keep hydrated while she is nursing.

  1. Proteins

In addition to the immunological components mentioned above, breast milk contains casein and whey. These proteins allow for quick, easy, and efficient digestion to meet the needs of rapid tissue growth and repair.

  1. Carbohydrates

The most prominent carbohydrate is lactose, which gives milk its sweet taste and provides important fuel for growth.  Foremilk, the milk produced at the beginning of each feed, is richest in carbohydrates.

  1. Fats

As the length of a feed increases, the milk becomes richer in fat composition. This is called the hindmilk and it provides an important source of calories. Breast milk contains essential fatty acids in the form of long-chain polyunsaturated fatty acids (most notably arachidonic acid and DHA) which vary depending on the mom’s diet. The North American diet is typically higher in omega 6 fatty acids and lower in omega 3 fatty acids making it low in DHA.  DHA is important for infant eye, brain, and nervous system development. Therefore, DHA is often recommended in supplement form for the mother during pregnancy and lactation.

  1. Vitamins and Minerals

The micronutrients found in breast milk depend on the mom’s diet and as well as her body stores. Because of this, in addition to a good whole food diet, I always recommend a mother continue taking her prenatal vitamin for the entire duration of nursing.  Not only is this important to maintain nutrient-rich milk for the baby, but it is especially important for the mother, so she does not deplete her own body stores of these nutrients.

Important Vitamins that Breast Milk Lacks

  1. Vitamin K

It is important to remember that regardless of the diet or mom's supplementation, breast milk is extremely low in vitamin K, which is why a vitamin K shot or oral supplementation is recommended after delivery to prevent hemorrhagic disease of the newborn.

  1. Vitamin D

Additionally, although breast milk contains vitamin D, researchers believe the amount in breast milk is not a high enough dose. That is why the American Pediatric Association recommends that all breastfed infants be directly supplemented with 400 IU of vitamin D.  Understandably, this can be cumbersome and easy to forget in the fog of new parenthood. Thankfully, a longitudinal study from 2006 to 2014 found that when moms took 6,400 IU of oral vitamin D, it provided enough vitamin D in the breast milk to adequately supplement the infant to the same degree that 400 IU of direct supplementation does.

How Long Should Breastfeeding Last?

Breast milk can fulfill the sole nutritional needs of an infant for the first 6 months of life, or until the infant displays signs of readiness for solid food introduction. Even then breast milk remains an important component of an infant’s diet and continues to provide important nutrients and growth factors. The World Health Organization recommends that breast milk continue to be a part of a young child's diet for the first 2 years of life and beyond. The infant microbiome is dynamic and still developing up until 3 years of age, when it takes on a more stable adult-like pattern. As such, I believe whenever possible, breastfeeding is wonderful to continue for as long as it suits the needs of both the mom and infant. And again, even if formula needs to be introduced sooner than you expected or hoped, being able to express and introduce colostrum shortly after birth to a new baby is better than nothing.



Barriers to breastfeeding in the US:

The Prebiotic and Probiotic Properties of Human Milk: Implications for Infant Immune Development and Pediatric Asthma:

American Academy of Pediatrics: Benefits of Breastfeeding:

Infant Nutrition Council:

Human Milk Composition: Nutrients and Bioactive Factors:

Dr. Briana Sinatra

Meet Dr. Briana Sinatra

Dr. Briana Sinatra is a board-certified naturopathic doctor with a vibrant practice in the Pacific Northwest. There she focuses on women’s and family health, taking a holistic approach to healthcare by empowering women with the knowledge and tools they need to live their best life now and protect their future wellness by looking at how all the systems in the body work together and how diet, lifestyle, and environment all influence health.

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