In this introductory overview, I explore the observation that breast milk is the gold standard for protective nutrients fed to newborn infants and present clinical evidence of its strong protective effect against age-related infectious gastroenteritis. The composition of breast milk changes according to the newborn infant’s needs for passive protection. In addition, substances in breast milk can actively stimulate development of the newborn’s host defenses to provide continued mucosal protection after breastfeeding is terminated. Later I present several specific examples of the development of intestinal host defenses due to breastfeeding. An important function of early breastfeeding is its anti-inflammatory effect on the immature, excessive inflammatory response in newborns. Several components of breast milk can reduce the inflammatory response to stimuli in the newborn intestine. These include transforming growth factor (TGF)-β, interleukin (IL)-10, erythropoietin, and lactoferrin. These components of breast milk can act individually or in concert to contain the neonatal immature anti-inflammatory response.