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A study by the University of California in Los Angeles found that 40% of babies’ beneficial intestinal bacteria came from breastfeeding, supporting the benefits of breast feeding and suggesting that babies who do not breastfeed need some other way to get these bacteria.


These bacteria are important for digestion and immune system training. Irregular amounts of gut bacteria have been shown in other studies to be correlated with weakened immune systems and increase susceptibility to allergies and diseases such as type 1 diabetes, asthma, and inflammatory bowel disease. Alternatively, individuals with strong gut microbiomes tend to be healthier.


Over the course of the year-long study, which contained 107 mother-infant pairs, researchers collected samples of the participating mothers’ breast milk and the participating babies’ stools, as well as swabs from the skin surrounding the mothers’ nipples. They found that 30 percent of the babies’ gut bacteria came from the breast milk, with another 10 percent from the breast skin.


The University of California study is just one of the recent studies that points to the importance of breastfeeding to the colonization of gut bacteria in infants. In September of last year, a similar study conducted by the University of Queensland concluded that breast milk also helped feed the bacteria that were already established. They found that breast milk contained human milk oligosaccharides, abbreviated as HMOs. Although the infants couldn’t actually digest the HMOs, they were nonetheless the third largest ingredient in the breast milk. The study concluded that, rather than feeding the child, these HMOs fed and encouraged the growth of the child’s gut bacteria.


This study also showed that a certain segment of mothers –about twenty percent– did not secrete HMOs, due to an inactive gene. The children of these mothers tended to have less healthy microbiomes of gut bacteria. Researchers hope to find a supplement for non-secreting mothers so that their babies would get an adequate amount of HMOs. But babies who don’t breastfeed at all won’t be able to get these HMOs at all.


These studies help gain some insight into where babies’ microbiomes come from, and how they are sustained. Still, much of how babies get their gut bacteria remains a mystery. Additionally, the study did not address how babies who are not breastfed build and maintain healthy microbiomes. More study will need to be done. Still, hopefully, a better understanding of the establishment of gut bacteria will lead to better health both during infancy and later in life.