The human gut comprises an essential barrier between the external environment and the body. When compared to other organs, it is unique in its multiple roles and the environmental challenges to which it is exposed. The human microbiome, in contact with the gut mucosa, provides a complex antigenic challenge to the mucosal immune system. However, immune tolerance enables a symbiotic relationship to exist, whereby the gut microbiota provides nutrition to the intestinal mucosa through short chain fatty acids, and the human gut provides a habitat for the microbiota.
However, when immune tolerance is lost, inflammation ensues. Inflammatory bowel disease (IBD) comprises Crohn’s disease (CD) and ulcerative colitis (UC). These chronic diseases have no known cure and manifest as a constellation of symptoms including abdominal pain, diarrhea, rectal bleeding and weight loss. The peak age of onset is 15-40 years with considerable morbidity in young people, affecting education, employment, relationships and quality of life. Treatment comprises immune suppressing medications and surgery, although modification of gut microflora through diet, pro and antibiotics may be helpful.
Recent advances have demonstrated the importance of nutrition in the aetiology of IBD, particularly with interactions between diet and genetic polymorphisms. Complications of IBD also include simple micronutrient deficiencies, which are often under-recognised by clinicians. Less common but devastating is intestinal failure, which may result from recurrent inflammation or complications of repeated gut surgery. These patients require long term total parenteral nutrition (TPN), a costly treatment with significant associated morbidity and mortality or, rarely, intestinal failure.
Dietary manipulation may improve the symptoms of IBD through reducing inflammation in the form of exclusive enteral nutrition (EEN) or through reducing associated functional symptoms with low FODMAP diet. However, patients are confronted with a plethora of advice concerning appropriate diets with few data to support most recommendations. Future research must focus not only on the efficacy of specific diets for IBD, but also the mechanisms behind potential benefits.
Finally, an in depth understanding of perturbations of the gut microbiota in IBD may give insights into the pathogenesis of other illnesses such as irritable bowel syndrome (IBS). While inflammation may only play a small part in the pathogenesis of IBS, it may also enable us to define a healthy gut and develop foods and diets that improve or prevent gut disease.
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