Crohn's disease causes part of the digestive tract to become inflamed. Many Crohn's disease sufferers have above average sugar in their diet, which may contribute to the cause of the condition or make the condition worse. There is also evidence that the increased permeability of the bowel wall causes nutrients to be inadequately absorbed, which means that higher quantities are required. Food allergies and intolerances may also contribute to the condition and some think that the immune system has become overactive.