The disorder can be debilitating in some patients, whereas others may have mild or moderate symptoms. All these diseases are characterized by inflammation that might be triggered by the translocation of luminal components into the host. Irritable bowel syndrome (IBS) is a functional gastrointestinal disease with a high population prevalence. In the final part, we discuss selected diseases associated with increased intestinal permeability such as critically illness, inflammatory bowel diseases, celiac disease, food allergy, irritable bowel syndrome, and-more recently recognized-obesity and metabolic diseases. The barrier assessments are further hindered by the natural variability of this functional entity depending on species and genes as well as on diet and other environmental factors. The means vary enormously and probably assess different functional components of the barrier. In the fourth part, the means to assess intestinal permeability are presented and critically discussed. In particular, potential barrier disruptors such as hypoperfusion of the gut, infections and toxins, but also selected over-dosed nutrients, drugs, and other lifestyle factors have to be considered.
Third, the regulation of intestinal permeability by diet and bacteria is depicted. Such opposing goals are achieved by a complex anatomical and functional structure the intestinal barrier consists of, the functional status of which is described by 'intestinal permeability'. On the one hand, an intact intestinal barrier protects the human organism against invasion of microorganisms and toxins, on the other hand, this barrier must be open to absorb essential fluids and nutrients. This barrier represents a huge mucosal surface, where billions of bacteria face the largest immune system of our body. Secondly, the key element of the intestinal barrier affecting permeability are described. First, the relevant terms 'intestinal barrier' and 'intestinal permeability' are defined. In the present review, current knowledge on mucosal barrier and its role in disease prevention and therapy is summarized. However, these terms are poorly defined, their assessment is a matter of debate, and their clinical significance is not clearly established. Data are accumulating that emphasize the important role of the intestinal barrier and intestinal permeability for health and disease.