Breast Milk is Medicine for Babies

An infant’s microbiome influences motor, social and cognitive development. 


  • Lack of breast milk in the first year is associated with developmental delays through the microbiome-gut-brain axis.
  • Breast milk promotes Bacteroides dominance in the microbiome.
  • Bacteroides-dominance in the gut of one-year-olds is associated with greater brain volume and healthy development.

As social mammals, human beings have until recently provided their version of the social mammalian “nest” to their young. Social mammals emerged over 70 million years ago with particular nurturing practices. Humans who likely emerged around 6 million years ago, followed similar practices. Humanity’s evolved nest includes not only warm, responsive care from multiple reliable, known others, but extensive touch, outdoor play, and breastfeeding.

Among First Nation Peoples, breast milk is understood to be the child’s first “medicine.”

An increasing number of scientific studies are demonstrating why calling human breast milk “medicine” may be more than a metaphor. And because it is National Breastfeeding Month, it is important to keep up with the research showing how important breastfeeding is for the nation’s children.

In the last decade, the microbiome—the type and balance of microorganisms in the gut (where most of the immune system resides)—has been examined in terms of mental and physical health.

The microbiome is influenced by various infant experiences. One of the most obvious experiences is ingestion of human breast milk and the act of breastfeeding. Breast milk is alive with microorganisms, stem cells, leucocytes and all the immunoglobulins that comprise a healthy immune system.

recent paper demonstrated that an infant’s microbiome affects their cognitive and language capacities later. Specifically, fecal samples were taken at four and twelve months and predicted cognitive capacities at age 2. Specifically, Bacteroidetes gut microbiota in late infancy were positively related to subsequent neurodevelopment, especially among males. Females were found generally to have more Bacteroidetes.

Listen to Kindred’s podcast interview with Jaysha Lyons-Hawk, Native Breastfeeding Week founder.

According to the authors, Bacteroidetes appear to be critical in late infancy when myelination and expanded connectivity of neuronal networks normally occur, promoting neurodevelopment during a critical time. If such processes are slowed, pervasive developmental delay may result. Developmental disorders now affect 13.4% of children aged 6 to 17.

Neurodevelopment is primarily driven by environmental factors. The gut microbiomes are altered in developmentally delayed children, such as those with autism.

“Bacteroides-dominance to be characteristic of 1 years olds with large gray-matter volumes in the superior occipital gyrus, the back region of the brain also shown to have reduced integration with other brain networks in preschool children with autism versus controls” (Taman et a., 2021, p. e1930875-10).

Brain functions and behavior are influenced by the signaling pathways of the microbiome-gut-brain axis. Boys are more susceptible to disruptions in this axis, which in animal studies affects the brain’s serotonergic system.

Breast milk is not the only experience that influences the presence of Bacteroidetes. Caesarean birth depletes Bacteroidetes. However, formula-fed infants who live with a dog or close to nature have microbiomes more like those of exclusively breastfed children.


Sukhpreet K. Tamana, Hein M. Tun, Theodore Konya, Radha S. Chari, Catherine J. Field, David S. Guttman, Allan B. Becker, Theo J. Moraes, Stuart E. Turvey, Padmaja Subbarao, Malcolm R. Sears, Jacqueline Pei, James A. Scott, Piush J. Mandhane & Anita L. Kozyrskyj (2021) Bacteroides-dominant gut microbiome of late infancy is associated with enhanced neurodevelopment, Gut Microbes, 13:1, 1930875

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