A food intolerance, or a food sensitivity occurs when a person has difficulty digesting a particular food. This can lead to symptoms such as intestinal gas, abdominal pain or diarrhea. A food intolerance is sometimes confused with or mislabeled as a food allergy*. Food intolerances involve the digestive system. Food allergies involve the immune system. With a food allergy, even a microscopic amount of the food has the potential to lead to a serious or life-threatening reaction called anaphylaxis.