Babies who breastfeed have a wider variety of bowel bacteria than those who are formula-fed. Why is this important? Because the bacteria in the newborn bowel (also known as the gut microbiota) help direct the development of the newborn’s immune system, among the many other beneficial functions they perform. A more diverse gut microbiota is associated with a healthier immune system.
We already know that babies born by cesarean section have a less-diverse gut microbiota than vaginally-born babies, and that following a c-section the newborn gut microbiota is often dominated by bacteria picked up from the hospital environment. Some of those hospital bacteria–clostridium difficile in particular–are associated with a number of nasty diseases in humans. From the looks of this study (and others), formula feeding may exacerbate the problem.
Nature intended for us to have a diverse gut microbiota, dominated by the types of bacteria picked up in the course of a vaginal birth and breastfeeding. We’re only now learning of the long-term health consequences of tinkering with that plan…
PS: In no way am I criticizing women who, for whatever reason, formula feed their babies. Exclusive breastfeeding isn’t always an easy thing to do in this day and age. But however it happens that a baby isn’t breastfed, the potential health impacts are the same.