Environmental and lifestyle influences on disorders of the large and small intestine: implications for treatment.

There is growing evidence that many aspects of our lifestyle and the environment we now live in contribute to the development of disease. The luminal digestive tract is a clear target of the influence of dietary components, alcohol, microbial organisms, and other ingested materials. External factors including obesity, lack of physical exercise, and tobacco consumption also impact diseases of the luminal gastrointestinal (GI) tract. A growing understanding of the microbiome which forms an integral part of the human organism indicates that this is another important external force that impacts human health and disease. The luminal GI tract conditions that arise, at least in part, from these external factors range from malignancies (squamous cell esophageal cancer, Barrett's esophagus and associated esophageal adenocarcinoma, gastric cancer, and colorectal cancer), idiopathic inflammatory disorders such as inflammatory bowel diseases, and post-infectious syndromes including post-infectious irritable bowel syndrome, post-infectious dyspepsia and other functional GI disorders. Of particular interest, given their increase in prevalence in much of the world, are immune-mediated conditions in which food antigens are the driving force behind disease development. These entities include celiac disease, eosinophilic esophagitis, and food allergies. Celiac disease is a prime example of a condition mediated by dietary factors whose pathogenesis has only recently been determined, providing opportunities for developing treatment options beyond the gluten-free diet. While a genetic basis for this disease clearly exists, it is believed that environmental factors such as an increase in gluten in the human diet account for its rising prevalence, now roughly 1% of genetically susceptible populations in all continents. Proposed therapeutic strategies span from preventing disease by modulating the time of gluten introduction in infants, to reducing exposure to gluten by developing strains of wheat with lower levels of gluten, degrading ingested gluten peptides within the intestinal lumen via endopeptidases or modulating uptake of these peptides across intestinal tight junctions. Other novel treatments in development focus on interfering with the immune events that lead to disease once gluten accesses the lamina propria including altering the immune milieu from a Th1-predominant response via hookworm infection, inhibiting tissue transglutaminase, and blocking antigen presentation and/or T-cell responses to gluten peptides. While new treatment options for celiac disease reflect the complex interaction of diet, genetic factors and the host immune response, the implications for treatment of many conditions of the large and small intestine that arise from environmental and lifestyle are as basic as ensuring adequate nutrition, regular exercise and cessation of tobacco use. Much more needs to be learned about the microbiome, dietary and other factors and their interaction with the human host in order to develop potential new treatment strategies for diseases that result from the environment and lifestyle.