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Breastfeeding and the infant gut microbiota at
12 months of age

Written by
Dr Fathalla Ali, PhD Paediatrics


From birth, infants acquire their mother’s microbiota. This process of acquisition is influenced by several factors, including mode of delivery, antibiotic exposure and breastfeeding. Feeding human milk to newborn infants has important nutritional, physiological, immunological and psychological benefits that may impact on their long-term growth and development. The World Health Organization recommend exclusive breastfeeding for the first 6 months of life and for it to continue in combination with other complementary foods for at least one year of life. In a recent study, Haddad et all, investigated the association between a mother’s pre-pregnancy Body Mass Index (“BMI”), human milk exposure, infant Body Mass Index-for-age z-score (BAZ) at 12 months of age and infants gut microbiota at 12 months of age. Stool samples were collected from pregnant women in their third trimester of pregnancy and later from their infants at 12 months of age. Findings from this study found that:

  • The feeding of infants with human milk at 6 months and 12 months of age was mainly determined by the pre-pregnancy BMI of the mothers.
  • Mothers with normal per-pregnancy BMI (BMI ≤ 25) were able to provide their infants with more breastmilk at 6 months and 12 months than mothers with high pre-pregnancy BMI (BMI ≥25).
  • The low rate of breastfeeding among infants born to obese mothers most likely was due to physical, physiological and psychological factors that negatively impacted on their ability to initiate or continue breastfeeding.
  • The growth of babies at 12 months of age was associated with the pre-pregnancy BMI of their mothers. Babies with high BMI-for-age z-scores (BAZ) were born to mothers with high pre-pregnancy BMI.
  • The BAZ of infants at 12 months of age was not associated with the mothers’ gut microbiota or human milk exposure.
  • Infants who were not breastfeeding at or beyond 6 months had a very distinct microbiota. It’s believed that the duration/exposure to human milk during the first year of life has a significant effect on gut microbiota development.
  • The increase duration in human milk exposure was associated with a reduction in gut microbiota richness. This reduction was attributed to the selective effect of human milk oligosaccharides to promote the growth of beneficial bacteria such as Bifidobacterium longum subsp. infantis and some Bacteroides
  • The gut microbiota diversity at 12 months of breastfed infants was not significantly different from infants not exposed to human milk or those exposed to human milk at 6 months only.

“These results underscore the importance of maternal wellbeing and healthy child-rearing practices on the establishment of the gut microbial community and the influence on infant BAZ, which have implications on health outcomes in later life and public health in general”, Authors of this study said.

Keywords: Human milk, Breastfeeding, Body Mass Index, Microbiota, obesity, per-pregnancy, Bifidobacteria, Bacteroides


Haddad, E. N., Sugino, K. Y., Kerver, J. M., Paneth, N., & Comstock, S. S. (2021). The infant gut microbiota at 12 months of age is associated with human milk exposure but not with maternal pre-pregnancy body mass index or infant BMI-for-age z-scores. Current research in physiology4, 94–102.

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