A number of factors can cause diarrhea after eating. A person can eat food contaminated with bacteria or a virus and experience diarrhea. Some people have trouble digesting foods that contain certain sugars, such as fructose or lactose, which can also cause diarrhea after eating. In some cases, a digestive disorder, such as Crohn's disease or ulcerative colitis, can cause diarrhea after a person eats certain types of food.
Several types of bacteria can cause diarrhea after eating, including pathogenic strains of E. coli, campylobacter and salmonella. E. coli strains usually are responsible for traveler's diarrhea, which occurs when a person eats contaminated, raw foods such as vegetables or fruit or when a person drinks contaminated water. In addition to diarrhea, E. coli can also cause nausea and vomiting. Some people can experience traveler's diarrhea caused by another type of bacteria, such as campylobacter or shigella. Diarrhea caused by E. coli usually clears up within a week, but it can take longer for an infection caused by campylobacter or other bacteria to resolve.
Foods can also be contaminated with viruses or parasites, leading to diarrhea. The Norwalk virus and other caliciviruses can be spread to people through foods. For example, if an ill person prepares a dinner, he or she can spread the virus to those who eat it. Parasites that cause bacteria are usually spread through drinking water, although they also can enter the body through contaminated food.
If a person is lactose intolerant, he or she might also experience diarrhea after eating certain dairy products. Many people cannot digest lactose, which is a sugar in milk and other types of dairy products, because they lack the enzyme required to break down the sugar. Typically, a person will experience diarrhea and other symptoms within a few hours of eating dairy products. Not eating dairy products or choosing dairy products that are lactose-free can help control and prevent the symptoms.
Other food sensitivities can cause diarrhea after eating. Some people might experience a reaction if they consume foods that have high amounts of sugar alcohols, such as sorbitol. Other people might have fructose intolerance, which prevents their bodies from breaking down and digesting the sugar commonly found in fruits and other sweets, such as soda and candy.
People who suffer from conditions such as irritable bowel syndrome (IBS) or Crohn's disease can also experience diarrhea after eating. The trigger foods vary from person to person for those who have IBS or Crohn's as well as other digestive disorders. People who have an allergy to wheat or celiac disease might also have digestive troubles after they eat foods that contain wheat or gluten.