The full term new born infant is capable of sucking and swallowing at birth and becomes efficient at it in a few days. He is not able to swallow solid foods till about four months of age due to extrusion reflex which makes him push out solids rather than swallow them. Once this reflex disappears, the infant slowly learns to swallow solids. It is important to spoon feed the child at this stage.
The stomach of an infant is smaller and functionally immature as compared to that of an older child. The concentration of gastric secretions such as hydrochloric acid and enzyme pepsin are low initially which prevent some types of food, as well as larger quantities from being digested. Enzyme secretions of pancreas and small intestine are low in early infancy.
Renal system of the infant is also immature during the first few months and so it is justified if solids are not introduced early. The immature kidneys cannot handle a higher solute load and if concentrated foods are given at this stage, it leads to excessive water loss and dehydration. Once solid food is introduced, it is important to regularly offer water to the infant.