Diet, food components and the intestinal barrier

The majority of dietary nutrient absorption occurs in the small intestine, with the intestinal epithelium acting as a barrier to the contents of the intestinal lumen. This barrier is maintained by intestinal epithelial cells, which support nutrient uptake but prevent translocation of bacteria, allergens and toxins. There is complex signalling and interaction between intestinal epithelia, macrophages, luminal contents and the microbiota which can modulate epithelial paracellular porosity. Intake of alcohol, fatty acids, pharmaceuticals and pathogenic bacteria has been reported to increase paracellular permeability, increase production of pro-inflammatory cytokines and temporarily reorganise tight junctional proteins. Conversely, numerous probiotics, nutraceuticals and food-derived bioactive components are promising due to reported restoration of intestinal barrier integrity by increasing production of anti-inflammatory cytokines and increased expression of tight junctional proteins. In vitro co-culture models exist and recent advances in microfluidic in vitro models are promising tools for investigating the complex effect of dietary components on the intestinal barrier. Temporarily perturbing the intestinal barrier may increase the oral bioavailability of therapeutic molecules. However, people with impaired intestinal integrity (e.g. those with Crohn's, coeliac or ulcerative colitis disease) should avoid foods which further perturb barrier integrity, while increasing intake of specific foods and possibly probiotics to promote intestinal barrier restoration.