It is well known that the intestinal barrier is altered in celiac disease (CD), an autoimmune disease that develops in genetically predisposed subjects exposed to ingestion of wheat gliadin and of related prolamines of barley and rye. More recently, defective epithelial barrier has been implicated in the pathogenesis of other conditions such as irritable bowel syndrome (IBS). At present IBS is still considered a functional condition although low-grade inflammation has been associated with its manifestation, particularly that following infection. Different substances have been implicated in the (dis)regulation of intestinal barrier, among them zonulin seems to play a key role. Other gastrointestinal peptides are GPL-2, Ghrelin, and Epidermal growth factor (EGF). In order to shed light on the hormonal regulation of intestinal barrier function in celiac patients before undergoing a gluten free diet and possible differences with those of IBS patients, in the present study the investigators will apply the non-invasive lactulose/mannitol permeability test toward the evaluation of intestinal damage. The pattern of intestinal permeability and the GI peptides concentration will be compared in celiac patients, IBS patients and healthy controls.