MONDAY, Jan. 11, 2016 (HealthDay News) -- A vaginal birth and breast-feeding make a notable difference in the bacterial composition of an infant's gut, according to new research.
At issue is the gastrointestinal makeup of the microbiome, the collection of microbes mainly in the large intestine that are essential to the immune system and good nutrition.
By tracking the birth and feeding records of more than 100 infants who were only 6 weeks old, investigators found that those born vaginally had a different gut composition from those delivered by cesarean section.
Differences were also seen between babies exclusively breast-fed compared with those fed with either formula or a mixture of formula and breast milk.
However, it was not clear whether such differences affect a baby's short-term or long-term health, study co-author Anne Gatewood Hoen said.
"Our study doesn't establish links with health outcomes at this time," said Hoen, an assistant professor of epidemiology and of biomedical data science with the Geisel School of Medicine at Dartmouth College in Lebanon, N.H.
But Hoen and lead author Dr. Juliette Madan, a neonatologist and assistant professor of pediatrics at Geisel/Dartmouth, noted that their team was "surprised to find that even at six weeks following birth, the gut microbiome seems to be shaped by delivery mode as much as it is by feeding method.
"This suggests that the major encounter with bacterial life that occurs during the process of birth is very important in the establishment of the gut microbiome and that its effects are lasting," the researchers said.
The authors noted in the study that "cesarean delivery has been associated with an increased risk for obesity, asthma, celiac disease and type 1 diabetes mellitus," and, compared to formula feeding, "breast-feeding has been related to decreased risks for illnesses such as asthma, obesity, infection, metabolic syndrome and diabetes."
Hoen and Madan outlined their findings in the Jan. 11 online edition of JAMA Pediatrics.
Roughly two-thirds of the infants in the study had been born vaginally, with the remaining third delivered via C-section. Similarly, about two-thirds had been exclusively fed breast milk in the first six weeks of life, while 26 were fed with a combination of breast milk and formula. Six were fed only formula.
Stool analyses revealed that a baby's delivery method had at least as much of an impact on the gut differences as diet.
The research team also found that infants fed a mix of formula and breast milk ended up with a gut composition at six weeks that was pretty much the same as those fed formula alone, a finding not previously noted in prior investigations.
What this all means for the health of babies as they grow remains unclear. Nevertheless, Hoen and Madan said that their results "support the current recommendations for vaginal delivery if at all possible, avoiding cesarean section unless medically necessary, and for exclusive breast-feeding when possible."
Dr. Mark Corkins, a certified nutrition support clinician from the University of Tennessee Health Science Center in Memphis, wasn't surprised by the findings.
"It obviously makes a difference how you're delivered," he said. "The unborn child's gut doesn't have any bacteria while in the uterus, of course. When they're inside mom, inside the amniotic fluid, there's no bacteria in there. So you only get colonized after birth, when you get a mouthful of bacteria during delivery, if you come through the vagina, because the vagina isn't sterile.
"But if you're born by C-section, the belly is scrubbed down with disinfectant in a sterile operating room," explained Corkins, who also serves as division chief of pediatric gastroenterology at Le Bonheur Children's Hospital in Memphis. "So you don't get the same flora. You get what's basically in the hospital.
"And then after you're born, if you're fed formula -- which is nutritionally complete -- you're still not getting all the other things in breast milk that a formula can't replicate: Growth factors, and things that foster the growth of certain good bacteria that we're designed to have in our colon.
"So while the microbiology techniques now being used to look at this issue are getting better, this isn't really a brand-new finding," he added. "We know that the route by which you're delivered matters, as does what you're fed once you're born. Both make a difference."
There's more on gut bacteria and the microbiome at the University of Washington.