• -Natalie

Shaping the Gut Microbiota by Breastfeeding - Research Study Summary

Updated: Oct 13, 2020

There is a lot of evidence beginning to emerge in medical journals showing that the gut microbiome is extremely important in the development of allergy. Read about the importance of the gut microbiota in one of my previous research study summaries.

This particular study about breastfeeding (referenced at the bottom of this article) focuses it's attention on the "window of opportunity" in early life. Evidence shows this may induce long-term effects in health and disease. Below, I will summarize the main takeaways from each section of the study.

Why Breastfeeding as a Potential Strategy for Allergy Prevention by Microbiota Shaping

Apparently, the order and timing by which the gut is colonized by microbes in early life has a lasting impact on the microbiome. This also has an impact on the variation of microbiota observed between individuals (different individuals may contain a variety of different microbes in their gut). Breastmilk contains factors that can affect key players in allergy development. This includes gut barrier function, the gut microbiota, and oral tolerance induction.

Modulating Early Life Gut Microbiota May Reduce Long-Term Allergic Disease Risk

Microbial diversity after birth (meaning the gut contains a highly diverse set of bacterial genes), helps prevent IgE induction (high levels of the IgE antibody which plays a main role in anaphylaxis and other allergic diseases).

It was shown that antibiotic treatment in early life exacerbated allergic airway inflammation, reduced regulatory T cells in the colon, and increased level of IgE antibodies.

In a study called Canadian Healthy Infant Longitudinal Development (CHILD), it was demonstrated that a low diversity of bacterial genes in the gut microbiome in early infancy was associated with food sensitization. Specifically, it was found that too much Enterobacteriaceae and too little of Bacteroidaceae were associated with food sensitization.

Furthermore, in subsequent studies, early colonization of a specific bacterium, Lactobacilli, was shown to decrease the risk of allergy. On the other hand, early colonization of the bacterium Staphylococcus aureus and Clostridium difficile characterizes infants developing allergy later in life.

Breastfeeding Shapes Gut Microbiota Composition and Metabolism in the Neonate

Evidence shows that microbial transfer from the mother to the fetus already occurs in utero. However, the first major exposure of the baby to microbes actually happens during birth. This is highly dependent on the mode of delivery though.

Other than birth mode and antibiotics just before or after delivery, early nutrition is a key factor in the composition of the gut microbiome. Nutrition provides nutrients for bacterial growth and dictates their production of metabolites (products of small molecules by the bacteria).

Not only is nutrition early in life a key factor in the development of the microbiome, but a large, multi-center study confirmed that breastfeeding specifically was the most significant factor associated with microbiome structure in early life.

It was shown that relatively small amounts of formula supplementation of breastfed infants already resulted in shifts of the microbiome composition even in the first day of life.

The microbiomes of newborns and young infants contain many genes that are required to digest sugars from breastmilk. These sugars from breastfed serve as prebiotics, which end up inducing the growth and activity of beneficial bacteria.

The introduction of solid foods changes the function of the gut bacteria because the genes involved in the digestion of these sugars are less needed and not used.

An interesting finding is that the microbiome composition of African and European infants is actually very similar until the introduction of solid foods. This shows the more important role of diet compared to other variables in shaping the microbial composition of the gut in early. Even more interesting is that changes in the microbiota of breastmilk is aligned with the changes of the baby's gut microbiota over time.

Lastly, secretory IgA (an antibody, not the same as IgE) also plays an important role in shaping the gut microbiome of the baby. IgA is an antibody, and the cells that produce IgA are found in the mother's gut and travel to the breast milk.

Newborns produce only low levels of IgA, so these IgA antibodies from breastmilk prevent expansion and penetration of pathogenic bacteria in their gut, while their intestinal immune system is still forming.

Studies show that IgA has the ability to shape bacterial composition, gene expression, and metabolic functions of the gut microbiota in the baby.


Breastfeeding shapes the gut microbiota in early life, both directly by exposure to the milk microbiota, and indirectly by maternal milk factors that affect bacterial growth such as breastmilk sugars and IgA antibodies.

My Personal Takeaway

It's important to realize that sometimes, some of the factors mentioned such as mode of delivery or breastfeeding is out of a mother's control. This is not the end of the world, and it still does not necessarily mean that the baby will develop food allergies. Babies can still survive from formula and live long, healthy lives. Many factors go into the development of food allergies. If a mother is able and willing to breastfeed, then according to this study, it is the best option in the role of allergy prevention. But again, not breastfeeding does not automatically mean that the baby will develop food allergies, and it's important to remember that. Breastmilk is only one factor that can have an effect on the microbiome, among many others, which then has an effect on the development of food allergy.

Title: Shaping the Gut Microbiota by Breastfeeding: The Gateway to Allergy Prevention?

Authors: Lieke W.J. van den Elsen, Johan Garssen, Remy Burcelin, and Valerie Verhasselt

doi: 10.3389/fped.2019.00047

Date Published: 27 February 2019

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