Why breast-fed premature infants have healthier guts than formula-fed ones

Human breastmilk has long been considered "liquid gold" among clinicians treating premature infants in a newborn intensive care unit (NICU). Breastmilk-fed "preemies" are healthier, on average, than those fed formula. Why is that true, however, has remained a mystery.
Human breastmilk has long been considered «liquid gold» among clinicians treating premature infants in a newborn intensive care unit (NICU). Breastmilk-fed «preemies» are healthier, on average, than those fed formula. Why is that true, however, has remained a mystery.