Factors that alter the normal transit of a meal through the alimentary canal will effect the consistency of the fecal contents. These insults can be specific or non-specific. Wheat flour contains gluten. In the absence of gluten hydrolase, gluten is converted to a toxic metabolite gliadin. Gliaden causes the destruction of enterocytes, and mucosal endocrine cells, severely limiting absorption in the jejunum.
Normal motility keeps bacteria restricted mostly to the colon.
Significant decreases in Motility in the small intestine which occur after surgery can lead to migration of bacteria into the small intestine, and this in turn can lead to a decrease in enterocyte viability and absorptive diarrhea. Furthermore, patients using H2 antagonists or other inhibitors of HCl secretion are susceptible to parasitic and bacterial infections which can lead to absorptive problems. Specific effectors which alter cAMP levels in enterocytes can lead to excessive secretion of ions and fluid into the colon. VIP is known to elevate cAMP in these cells during the post-prandial period. For this reason, VIP-oma's are correlated with massive secretory diarrhea.