This muscular coating is, in turn, controlled by a surprisingly complex nervous system. Diabetes can damage these nerves, and that may lead to gastrointestinal problems. First of all, many people with such GI problems have long-standing diabetes and evidence of damage to other organs. Finally, there are cases where people without diabetes have had GI nerves cut. Some of these people are then bothered by diarrhea.
Nerve damage occurs over the course of years.
But even people who haven't had diabetes for a long time may develop GI problems. A clear example is the person who develops diabetic ketoacidosis and experiences nausea, vomiting, and abdominal pain. There is now evidence that even short-term hyperglycemia may cause problems in the GI tract. Normally, your stomach's slow, steady, muscular contractions mulch solid food into tiny particles. Then your stomach pushes liquids and solids into your small bowel.