Functional bowel syndromes are constellations of upper and / or lower abdominal symptoms unexplained by adequate medical examination. The commonest forms are defined by symptom patterns and include bowel functional dyspepsia (FD), irritable bowel syndrome (IBS), functional bloating, functional diarrhea and functional constipation. These syndromes are the focus of much exciting research and diverse etiological hypotheses exist. The most common theories are based on changes in sensation (hypersensitivity), intestinal motility (muscle movement), intestinal permeability, enzyme or neurotransmitter function or changes in brain function. Some of these changes can occur after an infectious illness or protracted and severe stress.
Food intolerances and allergies are observed much more frequently in patients diagnosed with functional bowel syndromes. Lactose or fructose intolerance, for example, is observed in between 50% and 70% of IBS, patients, respectively. At present it is unclear if food reactions and functional bowel syndromes are separate causes of the symptoms, or if they represent overlapping or just overlooked diagnoses. It has been shown that malabsorption of sugars is equally common in healthy individuals as it is in patients with functional bowel syndromes. The malabsorption, however, leads to much more frequent and more intense symptoms of intolerance in patients with functional bowel syndromes. Furthermore, is has repeatedly been shown that dietary adaptations based on diagnosed food intolerances very significantly improve symptoms in IBS patients. Testing for food intolerances and, where indicated, food allergies, is therefore currently recommended and beneficial in individuals with functional bowel syndromes.