Investigating Markers of Intestinal Barrier Dysfunction in Gastrointestinal Diseases AJAMIANMARY AIDA 2019 This thesis studies circulating biomarkers of intestinal epithelial barrier integrity and function in human models. The results reveal that the protein zonulin, as it currently stands, is not a useful marker. However, a combination of other markers indicative of epithelial injury and and bacterial translocation provide insights into the heterogeneity of barrier dysfunction, localisation of intestinal injury, and modulation of the intestinal epithelium by diet and other factors.