Bacteria and parasites, lactose intolerance, artificial sweeteners and fructose are some of the causes of diarrhea after eating, notes Mayo Clinic. Crohn's disease, ulcerative colitis, celiac disease, microscopic colitis and irritable bowel syndrome cause chronic diarrhea, which may strike right after eating or at other times of the day.
Parasites such as Giardia lamblia and cryptosporidium in food and water can cause diarrhea, as can the bacteria campylobacter, salmonella, shigella and Escherichia coli, states Mayo Clinic. While contamination can occur in any setting, the bacteria and parasites that cause diarrhea are often present in the food and water of developing countries, so the condition is often called traveller's diarrhea. Some people are unable to process milk and other dairy products because they do not produce enough of the enzyme lactose, causing them to suffer from bouts of diarrhea after eating those foods. People have a higher risk of developing lactose intolerance as they age.
Artificial sweeteners, such as sorbitol and mannitol, that are present in chewing gum and other sugar free products can cause diarrhea, notes Mayo Clinic. Some people also suffer from diarrhea after consuming fructose, a sugar that occurs naturally in fruits and honey. Fructose is also sometimes added as a sweetener to beverages and causes diarrhea in people unable to process the sugar.