Antibodies that protect against harmful bacteria
Colonization of bacteria
A baby has a gut that is sterile at birth, but their gut quickly comes into contact with all types of bacteria. If the baby is given to the mother immediately after birth, most of the colonization of bacteria will come from the mother’s body. If any of the bacteria is harmful, she will pass the necessary antibodies to her baby as soon as she breastfeeds him/her.
Babies born via C-section or who are separated from their mothers at birth, are exposed to unfamiliar bacteria and may not receive the antibodies necessary for protection. A baby’s gut may be affected by the bacteria for months after birth.
Breast milk keeps the PH lower.
Breastfed babies have lower gut PH, which decreases the amount of E-coli, streptococci and clostridia bacteria in the gut. Formula fed babies have a higher gut PH, which allows for the growth of harmful bacteria. Even a single bottle of formula will disturb the gut flora and raise the PH level in a baby's gut.
Breast milk protects by coating the gut lining.
Mucous membranes of the gut
Babies are born with immature digestive tracts. The gut has wide spaces in the mucous membranes, which makes it easier for a baby to digest food. Breast milk contains sIgA, which coats these membranes and protects against whole proteins, that cause allergies and also protects against pathogens.
Tracy Behr, CBC, CLD (CBI)
Reference: Course information on the physiology of lactation and gut protection through breast milk.