Diet in the pathogenesis and treatment of inflammatory bowel diseases

Abstract

Some of the most common symptoms of the inflammatory bowel diseases (IBD, which include ulcerative colitis and Crohn's disease) are abdominal pain, diarrhea, and weight loss. It is therefore not surprising that clinicians and patients have wondered whether dietary patterns influence the onset or course of IBD. The question of what to eat is among the most commonly asked by patients, and among the most difficult to answer for clinicians. There are substantial variations in dietary behaviors of patients and recommendations for them, although clinicians do not routinely endorse specific diets for patients with IBD. Dietary clinical trials have been limited by their inability to include a placebo control, contamination of study groups, and inclusion of patients receiving medical therapies. Additional challenges include accuracy of information on dietary intake, complex interactions between foods consumed, and differences in food metabolism among individuals. We review the roles of diet in the etiology and management of IBD based on plausible mechanisms and clinical evidence. Researchers have learned much about the effects of diet on the mucosal immune system, epithelial function, and the intestinal microbiome; these findings could have significant practical implications. Controlled studies of patients receiving enteral nutrition and observations made from patients on exclusion diets have shown that components of whole foods can have deleterious effects for patients with IBD. Additionally, studies in animal models suggested that certain nutrients can reduce intestinal inflammation. In the future, engineered diets that restrict deleterious components but supplement beneficial nutrients could be used to modify the luminal intestinal environment of patients with IBD; these might be used alone or in combination with immunosuppressive agents, or as salvage therapy for patients who do not respond or lose responsiveness to medical therapies. Stricter diets might be required to induce remission, and more sustainable exclusion diets could be used to maintain long-term remission.

Keywords: Diet; IBD; Pathogenesis; Therapy.

Figure 1. Effects of Diet on the Intestinal Microbiota and Immune System During Development of IBD

There is evidence from epidemiologic, animal, and clinical studies that certain components of diet can promote or prevent against intestinal inflammation. Diet not only affects the composition of the gut microbiota but also serves as substrate for microbial synthesis of metabolites, which affect the mucosal immune system. Microbes also act the immune system of the intestinal mucosa, through the engagement of innate immune receptors with specific microbial products (mucosally-associated molecular patterns, MAMPS). In turn, the host mucosal immune system fortifies mucosal barrier function and interacts with the gut microbiota through the production of mucin, anti-microbial peptides (AMPs), and IgA.

Figure 2. Altering the Luminal Environment of the Intestine as an Adjunct Therapy for IBD

The luminal environment of the gut might be modified by alteration of the microbiome and/or diet to induce and/or maintain remission in patients with IBD. Such an approach might have value as an adjunct to currently used immunosuppressive agents, to increase response and/or reduce drug dose, or as salvage therapy for patients who do not respond or lose responsiveness to immunosuppressive agents.