The dumping syndrome, or rapid gastric emptying, happens when the lower end of the small intestine fills too quickly with undigested food from the stomach. The early symptoms of dumping syndrome are caused by a rapid flow of food into the intestines which lowers blood volume by drawing fluid from the blood into the intestines to dilute the food and causes a very high rise in blood sugar. Symptoms may begin during or right after a meal. These "early" dumping symptoms include nausea, vomiting, bloating, diarrhea, and shortness of breath. "Late" dumping happens 1 to 3 hours after eating. Symptoms of late dumping include weakness, sweating, and dizziness. Many people have both types.

Stomach surgery is the main cause of dumping syndrome because surgery may damage the system that controls digestion. In addition, people with this syndrome often suffer from low blood sugar, or hypoglycemia, because the rapid "dumping" of food triggers the pancreas to release excessive amounts of insulin into the bloodstream. Patients with Zollinger-Ellison syndrome may also have dumping syndrome.

Treatment includes changes in eating habits and medication. People who have dumping syndrome need to eat several small meals a day that are low in carbohydrates and should drink liquids between meals, not with them.