Baby’s Superfood: Using Breastmilk to Strengthen the Infant Gut
Breastfeeding popularity has ebbed and flowed over the last several decades, with August serving as an opportunity to highlight the importance of breastmilk. Research continues to shed light on just how essential breastmilk is for overall health, and as such, the World Health Organization now promotes exclusive breastfeeding for, and delaying solid foods until, after six months of age since breastmilk consumption during the first six months is crucial not only for physical growth, but also for the proper development of the baby’s gut microbiome.
>>Please note: this article is not intended to create shame for those unable to breastfeed, but merely highlight the importance of it for those who are able to breastfeed, or who can obtain supplemental breastmilk and may be considering formula instead.
If you’ve been following this blog for awhile now, you’ll recall that the gut microbiome is the seat of our overall health, both physical and mental. (You can refresh your memory here.)
The Developing Microbiome
The gut microbiome contains around 100 trillion microorganisms, including aerobic and anaerobic bacteria, archaea, fungi, parasites, and viruses. When discussing the human microbiome, we tend to mostly focus on the bacterial species. While many of the microbiome’s bacterial strains overlap for the majority of people, individual strain composition as well as quantities of the various strains are specific to each individual, much like a unique fingerprint.
We aren’t born with a robust adult microbiome; this happens by about age 2 (the concept of which is also termed “The First 1,000 Days”). While baby is busy using nutrition to develop appropriately and ward off infectious disease, so too does baby’s microbiome. During these first 1,000 days from conception to late infancy, babies’ gut microbiomes mature, undergoing an organized series of bacterial progressions, with certain strains modulating the gut environment to allow the next strains to colonize, and so on.
Infant gut colonization begins early on, with repeated new exposures to bacteria, It is thought that fetal guts begin microbial colonization even before birth via bacterial transfer from placenta and amniotic fluid, as meconium contains its own distinct microbiome. During the birth process, followed by infant feeding, the gut will continue to be colonized: Vaginal births provide microbial seeding during the trip down the birth canal with mom’s flora, while vaginal and C-section babies are also colonized by what they come into contact with during and just after birth, including microbes from birth attendants and the environment. Breastmilk and formula continue to modify the infant microbiome. About 25-30% of a breastfed infant’s microbes come directly from breastmilk (predominantly Staphylococcus, Streptococcus, and Pseudemonas bacteria). Breastmilk itself also selectively feeds certain strains residing in the gut, including specific types of Bifidobacteria, Bacteroides, and Lactobacilli. Formula can promote the growth of a variety of both desirable and undesirable bacterial strains. Mixed feeding can help to support more beneficial bacterial strains. By the time the infant diet consists fully of solids, the toddler gut microbiome begins to resemble that of an adult, featuring more diverse microbes.
The Gut-Immune System Connection
The gut is the center of roughly 70% of the immune system, so it comes as no surprise that the healthy ecology of our microbial friends is thereby critical for the immune system, not just in infancy but also into adulthood. How a baby’s immune system develops in those critical first few months and years can determine immune system function for decades to come. The gut bacteria play such an important role because the immune system requires the gut to be the body’s primary defense between the “outside” and “inside” worlds (think about all the things that we ingest all day long, and the microbes that come along for the ride!!).
When the bacteria are imbalanced, inflammation can ensue, creating an upset immune system responding to the dysbiosis. An upset immune system may display as rashes or hives, upset tummies and funky stools or reflux, skin eruptions, and other symptoms in response to ingestion of certain foods or environmental factors (e.g. cat or pollen allergies). On the opposite end, an upset immune system can become overreactive; this is when we start to see true allergies, asthma, and autoimmune diseases develop. Therefore, ensuring the correct microbial balance from infancy and beyond is a critical step in decreasing the risk of food allergies, inflammatory diseases, and autoimmune conditions. Taking it a step further, imbalanced immune systems have also been linked to conditions such as metabolic dysfunction (difficulty with regular blood sugar and breaking down fats, proteins, and especially carbohydrates), poor mental health, and more.
HMOs (Not of the restrictive insurance variety)
Returning to what we are feeding baby, breastmilk is a complete package, meeting all of baby’s requirements for water, fat, carbohydrates, protein, vitamins, minerals, immune system support (antibodies), some hormones, and more that are needed for a baby to grow and develop. But breastmilk also has a secret superfood ingredient: it contains incredibly important molecules called human milk oligosaccharides (HMOs), whose production is dependent on mother’s dietary pattern. HMOs are essential for gut and brain health. They are sugars undigestible to humans, though a few bacteria like Bifidobacterium infantis (a foundational probiotic bacteria in infants) and Bifidobacterium bifidus can digest and break down HMOs, which then release molecules called short chain fatty acids (SCFAs), which we will discuss shortly.
In addition to SCFA production, HMOs serve as a decoy for potentially pathogenic bacteria. These naughty microbes like to latch on to sugar molecules found in the intestinal tract, which promote their proliferation. Since HMOs bear a striking resemblance to these sugars, the harmful bacteria get confused and attach to HMOs in the baby’s gut instead, thereby protecting the baby from a potential overgrowth or infection that could create illness and inflammation. Some HMOs can be added to formula to mimic this special breastmilk feature, though the full range of HMOs is unavailable for supplementation.
Secretory IgA (SIgA): The Supplemental Immune Defense Mechanism
Breastmilk also contains secretory IgA (SIgA), a component of the immune system otherwise released by cells located throughout the digestive tract. SIgA helps to fight infections in the gut. (This important antibody isn’t just critical in infancy, rather it continues to be one of the primary gut immune defenses as we age.) When SIgA levels are disrupted, we may become more susceptible to environmental allergies, food allergies, sensitivities, and intolerances. Formula manufacturers have not, to our knowledge, been able to mimic the SIgA in breastmilk as an ingredient.
SIgA levels can be used as a measure of microbiome dysbiosis when very high or very low. This skewed microbiome may indicate that short chain fatty acid (SCFA)-producing bacteria are insufficient. This is significant because a specific type of SCFA, butyrate, is necessary for maintaining immune tolerance to food and serving as an energy source for human gut cells to repair themselves. Some SCFA-producing bacteria proliferate with breastmilk. Therefore, the augmentation of SIgA from breastmilk, as well as the enhancement of the immune system from the microbiome’s SCFA production, can be helpful in deterring the development of allergies in young children.
As you can see, there are many significant benefits to breastmilk beyond serving as a nutrition source for baby. Since babies are born with an immature immune system, breastfeeding is a critical component to supporting and developing their overall immunity. Given its highly nourishing composition and promotion of balanced gut flora, breastfeeding is now recognized as an important strategy to ensure a healthy balance of beneficial bacteria in an infant’s gut. With breastmilk’s ability to selectively feed beneficial bacterial strains, more pathogenic strains can be crowded out or reduced in frequency while butyrate production can be promoted for gut cell repair. And breastmilk’s role in priming healthy levels of SIgA in early life is essential for a robust immune system for years to come.
While it’s vitally important that our infants are being fed a nutrient-dense option, be it breastmilk or formula, if one has the chance, even a small amount of daily breastmilk can help support gut health and, potentially, decrease risk of immune system problems later in life.
If your child is showing signs of gut imbalances or immune system issues, we may be able to help! Feel free to schedule your complementary strategy session today to find out how!