Babies are born with a sticky tar-like substance called meconium in their intestines. Colostrum , or early milk, is uniquely designed to help move this substance through the infant's body. Breast milk contains immunities to diseases and illnesses and aids in the development of baby's immune system. Formula provides neither of these benefits. J. Ped Gastro Nutr 1989.
Breast milk is more digestible than formula.
Babies can digest human milk more easily than the milk of other animals, probably because human milk contains an enzyme that aids in this process. While it contains less protein than does cow's milk, virtually all the protein in breast milk is available to the baby. By contrast, about half the protein in cow's milk passes through the baby's body as a waste product. Similarly, iron and zinc are absorbed better by breastfed babies. The Complete Book Of Breastfeeding M.S. Eiger.