Abstract
Diet provides a safe and attractive alternative to available treatment options in a variety of diseases; however, research has only just begun to elucidate the role of diet in chronic diseases, such as the inflammatory bowel diseases (IBD). The chronic and highly debilitating IBDs, Crohn disease and ulcerative colitis, are hallmarked by intestinal inflammation, immune dysregulation, and dysbiosis; and evidence supports a role for genetics, microbiota, and the environment, including diet, in disease pathogenesis. This is true especially in children with IBD, where diet-based treatments have shown excellent results. One interesting group of dietary factors that readily links microbiota to gut health is dietary fibers. Fibers are not digested by human cells, but rather fermented by the gut microbes within the bowel. Evidence has been mounting over the last decade in support of the importance of dietary fibers in the maintenance of gut health and in IBD; however, more recent studies highlight the complexity of this interaction and importance of understanding the role of each individual dietary fiber subtype, especially during disease. There are roughly ten subtypes of dietary fibers described to date, categorized as soluble or insoluble, with varying chemical structures, and large differences in their fermentation profiles. Many studies to date have described the benefits of the byproducts of fermentation in healthy individuals and the potential health benefits in select disease models. However, there remains a void in our understanding of how each of these individual fibers affect human health in dysbiotic settings where appropriate fermentation may not be achieved. This review highlights the possibilities for better defining the role of individual dietary fibers for use in regulating inflammation in IBD.
Highlights
The etiology of the chronic and severely debilitating Inflammatory Bowel Diseases (IBD), Crohn disease (CD), and ulcerative colitis (UC), remains poorly understood and incidence rates are increasing, especially in children [1,2,3]
With an increasing focus on nutritional interventions, especially in children with Crohn disease, and the interest on specific use of probiotics and prebiotics in IBD, it is important that we broaden our understanding of how foods affect the bowel, especially in regards to the fiber fermentation processes that occur in the bowel
How do these in vitro and in vivo studies translate to the complex system of the human bowel? As this review highlighted, differences in microbial composition and dietary factors present can result in substantial differences in host inflammatory response [21]
Summary
The etiology of the chronic and severely debilitating Inflammatory Bowel Diseases (IBD), Crohn disease (CD), and ulcerative colitis (UC), remains poorly understood and incidence rates are increasing, especially in children [1,2,3]. The term has grown to include non-starch polysaccharides (e.g., cellulose, pectin), non-carbohydratebased polymers (e.g., lignan), resistant oligosaccharides (e.g., fructooligosaccharides, galatooligosaccharides), and carbohydrates considered to be of animal origin (e.g., chitin) [25] These dietary fibers can be found in a variety of food sources (Figure 2) and structurally differ in their chain length, linkage type, sugar components, and ability to associate with other chemical compounds (Figure 1) [25]. Non-digestible dietary carbohydrates (fiber and resistant starch) can withstand the acidity of the stomach and do not undergo degradation in the human small intestine [26]; instead they are fermented by the gut microbiota consortium within the large bowel (Figure 2) where one microbe starts the fermentation and others continue the fermentation process, thereby working together systematically This microbial consortium role highlights the potential implications of dysbiosis, which could alter or even prevent fiber fermentation. Animal studies have demonstrated that dietary fibers can inhibit IBD-associated inflammation [96,97,98], and clinical trials have shown that SCFA can prevent intestinal atrophy in IBD patients, allowing for tissue recovery [99]
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