Breast-feeding may contribute to the development of healthy bacteria in a baby's gut, a new study finds.
The results show that three-month-old babies that had been fed only breast milk had a wider range of bacteria in their guts than babies that were fed only formula.
The researchers also found a link between the bacteria in the babies' guts and changes in the expression of genes involved in their immune systems.
"The early neonatal period is a critical phase for both intestinal digestive development as well as colonization" by the gut bacteria, the researchers wrote.
The study showed an association, not a cause-and-effect link, between breast-feeding and a healthier infant gut, and more work is needed to confirm the findings.
Still, there are ways to plausibly explain how breast milk may bring about changes in a baby's gut bacteria and immune system, the researchers said. The greater diversity of bacteria seen in the guts of the breast-fed infants may bring about the activation of certain immunity genes, they wrote.
In the study, researchers looked for genetic material in stool samples from 12 infants — half of which were breast-fed, and half of which were formula-fed. They used the genetic material to identify the types of bacteria in the babies' guts.
The results showed that the immune systems of the breast-fed babies had developed to cope with the wider range of bacteria present in their intestinal tract. While the guts of the breast-fed infants showed they had more bacteria associated with "virulence," such as genes for resistance to antibiotics, the researchers also found increased activity of immunity genes known to be involved in defending the gut tissue against foreign invaders, said study researcher Robert Chapkin, a professor of Nutrition, Biochemistry and Biophysicsat the Texas A&M University.
"Our findings suggest that human milk promotes the beneficial crosstalk between the immune system and microbe population in the gut, and maintains intestinal stability," Chapkin said.
The study was published in the journal Genome Biology.