Breast milk is a complex, dynamic matrix of nutrients and bioactive agents, both of which are vitally important to the health and development of growing infants.  However, breastmilk offers even more; a diverse community of microorganisms that benefit mother-infant health. 

Previous studies have shown that breastfed and formula-fed infants have distinctly different microbiota composition in their gut.  For example, breast fed infants have a higher abundance of Bifidobacterium and Lactobacillus in the gut compared to formula-fed infants.  Beneficial bacteria found in breast milk help to colonize the infant’s gut, which may impact infant health for years to come.  For this reason, it is important to investigate factors that potentially influence the breast milk microbiota.

A study conducted by Erika Cortes-Macías (Institute of Agrochemistry and Food Technology IATA-CSIC) and colleagues examined the association between maternal diet and breast milk microbiota to ascertain the potential role of birth delivery method and antibiotic exposure on breast milk microbiota composition according to maternal diet.

Upcoming ASN Webinar: Research Designs to Account for Diversity and Inclusiveness and Impact Food Guidance Policy

March 11, 2022, 12:30 – 2:00 PM EST

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A total of 120 healthy mothers from the observational study Maternal Microbes cohort were included in this cross-sectional study. Maternal dietary information was recorded using a food frequency questionnaire, and clinical characteristics, including mode of delivery, antibiotic exposure, and exclusive breastfeeding, were collected.  Maternal diets were classified as 1) high intake of plant protein, fiber, and carbohydrates or 2) high intake of animal protein and lipids.

Study results, published in The Journal of Nutrition, found that breast milk microbiota was shaped by maternal dietary clusters.  Those in the high-carbohydrate group produced milk with a greater abundance of Staphylococcus and Bifidobacterium compared to those with high intakes of animal protein and lipids.  Furthermore, the mode of delivery and antibiotic exposure influenced breast milk microbiota in a diet cluster-dependent manner. These findings suggest that a complex interaction between different maternal and perinatal factors affects breast milk microbiota. A corresponding editorial by Michelle McGuire and Mark McGuire (University of Idaho) provides additional insights into the significance of the study results and a proposed path forward regarding research to better understand the power and potential of human milk as a unique and important food.


Cortes-Macías E, Selma-Royo S, García-Mantrana I, Calatayud M, González S, Martínez-Costa C, Collado MC. Maternal Diet Shapes the Breast Milk Microbiota Composition and Diversity: Impact of Mode of Delivery and Antibiotic Exposure. The Journal of Nutrition, Volume 151, Issue 2, February 2021, Pages 330–340,

McGuire MK, McGuire MA. Mapping the Human Milk Microbiome: Impetus for a Long-Awaited Renaissance in Maternal and Infant Nutrition Research? The Journal of Nutrition. The Journal of Nutrition, Volume 151, Issue 2, February 2021, Pages 278–280,

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