Supporting Breastfeeding

La Leche League Canada

Breastfeeding and Your Baby’s Gut

on September 21, 2015

The “gut microbiome” is the micro bacterial community that exists in the gut of every human being. There are billions of microbes and they change and adjust throughout our lives. The role of these microbes is known to be both digestive and protective.

Recent research confirmed previous studies which found that baby’s diet in the early months has a profound influence on the type and number of micobacteria in the gut as well as the stability of the microbiome. Regardless of whether babies are exclusively breastfed or receive mixed breastmilk and formula feeding the diversity in the microbiome increases from birth to 3 years. Exclusively breastfed babies have less diversity in the microbiome and a greater proportion of the bacteria being Bifidobacterium which are involved in breaking down the oligosaccharides in human milk. These “good” bacteria are known to inhibit harmful bacteria, modulate the body’s immune response and produce vitamins within the gut. Babies receiving formula have greater proportions of Bacteriodetes and Clostridiales microbes which are primarily involved in the digestion of proteins and carbohydrates.


What is interesting in the study’s findings is the children who had received formula prior to starting solids showed more marked changes in the gut microbiome after starting solids than the children who had been exclusively breastfed. This may seem counter-intuitive when the gut biome of the mixed feeding babies was already more diverse prior to the introduction of solids. The authors of the study feel the reason for the less dramatic change in the gut microbiome of the exclusively breastfed babies is that breastmilk has better prepared the gut for the introduction of new foods. Breastmilk composition varies daily according to what the mother is eating and this creates a greater degree of adaptability in the gut’s microbiome. They hypothesize that the microbiome of the babies who have received formula is less adaptable when faced with new foods because formula composition never varies.

The research also showed some interesting variability in the microbiome in relationship to iron. Breastmilk contains less iron than formula but breastfed babies generally are not found to be iron deficient. The reason is found in the gut microbes. The formula fed babies had higher numbers of the kinds of bacteria which use iron thus taking away the iron that should pass through the gut wall and into the blood stream. Breastfed babies on the other hand had less of the iron stealing bacteria and more of the bacteria which produce vitamin C which is needed by the body for the uptake of iron.

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In conclusion the study’s authors state that their findings “suggest that feeding-based differences in microbiome composition have the potential to contribute to the programming of infant metabolism and immune function. Such programming during the critical period of weaning with the transition from a milk-based to a more varied, solid-based diets characterized by higher levels of carbohydrates and animal proteins may have long-term consequences for not only the establishment of the adult microbiome but also the development of metabolic diseases like obesity, diabetes, cardiovascular disease, and non-alcoholic fatty liver disease.”

Whether or not you understand or even care about the science of the gut microbiome you can feel confident that exclusive breastfeeding until baby is interested in starting solids, around the middle of the first year, is setting up the conditions for your baby to have a healthy gut microbiome for the rest of his or her life.

If you need more information or have a breastfeeding problem or concern, you are encouraged to talk directly to an accredited La Leche League Leader.  In Canada, Leaders can be located by clicking or Internationally


If you have found this article helpful, La Leche League Canada would appreciate your support in the form of a donation at so we can continue to help others breastfeed.





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