Scientists have uncovered a potentially important role for an unexpected component of human breast milk, suggesting that urea, commonly recognized as a waste product of normal metabolism, may help influence the development of beneficial gut bacteria in newborn babies. Research reported on 9 November 2026 examined how urea concentrations change throughout breastfeeding and interact with microorganisms involved in establishing an infant's intestinal microbiome. Using human milk samples, microbial analyses and laboratory experiments, researchers found that urea levels increase during lactation and may be regulated by the mammary gland rather than simply reflecting a mother's diet. Certain concentrations appeared to support the growth of beneficial Bifidobacterium bacteria, while higher concentrations could favor other organisms, including potentially harmful bacteria. The research also identified differences between natural breast milk and commercially available infant formulas. Scientists believe the findings could improve understanding of early-life nutrition and the relationship between maternal biology and infant gut development. However, the study remains a non-peer-reviewed preprint, and further research is required before drawing clinical conclusions or recommending changes to infant feeding practices.
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