Reasons why newborns spit up a lot of milk: spitting up is a common thing during the newborn period. This may be due to the fact that the gastrointestinal function of newborns is not strong enough and the food cannot be fully digested. However, there are other reasons that cause newborns to vomit up a lot of milk, as follows: Over-feeding Newborns especially need milk to obtain nutrients, but if they are fed too frequently or for too long, the stomach will be overfilled, causing Vomit. Stomach