Passing stool immediately after eating can have various causes, including the gastrocolic reflex and certain medical conditions. The gastrocolic reflex is a normal physiological response in which the digestive system is triggered to move stool along the colon after eating a meal. Additionally, certain conditions such as Irritable Bowel Syndrome (IBS) or food intolerances can lead to more immediate bowel movements after eating. In these cases, specific foods or triggers may stimulate the intestines, resulting in the urge to have a bowel movement.