Enzymatic maturation of the gastrointestinal tract and its relevance to food allergy and intolerance in infancy.

The biologic clock that determines the temporal sequence of maturation of digestive and absorptive processes in the gastrointestinal tract is genetically predetermined, but may be modified by dietary, hormonal, or other factors. In general it may be said that the gastrointestinal tract of full-term neonates is capable of digesting and absorbing a nutritionally adequate quantity of dietary protein but capacity is limited. Very low birth weight preterm infants, who are surviving the early neonatal period in increasing numbers, have immaturity of a wide range of digestive and membrane-associated absorptive processes; in addition macromolecular absorption may be increased. Whether a limited capacity to digest food protein results in increased or altered antigenic stimulation of these immature infants remains speculative with present knowledge. Immaturity of intestinal lactase may lead to problems of lactose intolerance, but there is recent evidence that lactase activity may be inducible by milk feeding.