Background/Objectives: Our objective was to review published studies of the intestinal barrier and permeability, the deleterious effects of dietary components (particularly fat), the impact of altered intestinal permeability in disease models and human diseases, the role of the microbiome and epigenomics in control of barrier function, and the opportunities to restore normal barrier function with dietary interventions and products of the microbiota. Methods: We conducted a literature review including the following keywords alone or in combination: intestinal barrier, permeability, microbiome, epigenomics, diet, irritable bowel syndrome, inflammatory bowel disease, probiotics. Results: Intestinal permeability is modified by a diet including fat, which increases permeability, and nutrients such as fiber, glutamine, zinc, vitamin D, polyphenols, emulsifiers, and anthocyanins, which decrease permeability. There is significant interaction of the microbiome and barrier function, including the inflammatory of luminal/bacterial antigens, and anti-inflammatory effects of commensals or probiotics and their products, including short-chain fatty acids. Epigenomic modification of barrier functions are best illustrated by effects on junction proteins or inflammation. Detailed documentation of the protective effects of diet, probiotics, prebiotics, and microbiota is provided. Conclusion: intestinal permeability is a critical factor in protection against gastrointestinal diseases and is impacted by nutrients that preserve or heal and repair the barrier and nurture anti-inflammatory effects.

Acute severe ulcerative colitis (ASUC) remains a clinical challenge associated with considerable morbidity, including colectomy. Upadacitinib (UPA), a selective Janus kinase (JAK)-1 inhibitor, is approved for moderate-to-severe ulcerative colitis in patients intolerant or not responding to tumor necrosis factor-alpha inhibitors. It has also increasingly been used off-label for ASUC. We performed a systematic review of all available literature on UPA in ASUC. We identified 11 studies, with a pooled total of 55 patients. Most patients experienced rapid and sustained improvement. Colectomy rate at 90 days was 16.3%. Among those who did not get colectomy, 80% were in steroid-free remission at follow-up. The reported adverse events were low, including 2 venous thromboembolic events. Overall, UPA appears to represent a safe and effective therapy for ASUC.