Irritable Bowel Disease (IBD) is an umbrella term used to characterise disorders that cause chronic inflammation at various sites along the gastrointestinal tract, it includes both Crohn’s disease and ulcerative colitis.
Both conditions share similar symptoms, including urgent diarrhoea, rectal bleeding, abdominal pain and excessive gas. The severity of these symptoms can fluctuate significantly, with patients experiencing unpredictable flares and remissions. During flares physical symptoms can be severe and debilitating, with additional psychological disorders, such as anxiety and depression, frequently reported.
Despite their similarities, there are distinct differences which allow the two conditions to be differentiated.
Ulcerative colitis: involves continuous inflammation and ulcers along the lining of the large intestine (colon) and rectum.
Crohn’s disease: involves non-continuous sections of inflammation anywhere in the digestive tract, from the mouth to the anus. It can often penetrate through the intestinal lining and involve the deeper layers of the digestive tract.
Given the profound effect IBD can have on quality of life there is great interest by patients and healthcare professionals alike to identify potentially useful interventions for the management of the condition.
Pathophysiology
While the aetiology of IBD remains largely unknown, research has suggested that it likely involves a complex interaction between external environmental triggers, microbial environmental and genetic predispositions.. This interaction contributes to an inappropriate immune reaction and an exaggerated inflammatory response in the gastrointestinal tract.
It is not yet understood which factor plays the greatest role in the development and progression of IBD, but there is growing interest in the influence of the microbial environment.
Patients with IBD have been found to have an imbalanced composition of microbiota, known as dysbiosis. When compared with healthy individuals, patients with IBD have a lower microbial diversity, with a greater abundance of opportunistic bacteria (such as Bacteroidetes and Proteobacteria) and a smaller presence of beneficial bacteria (such as Firmicutes).
This imbalance translates to an increase in inflammatory cytokines such as tumour necrosis factor (TNF) and interleukins-6 and a decrease in beneficial metabolites such as butyrate. These changes allow for disturbances to the mucosal barrier, which contributes to intestinal inflammation and IBD development.5
Given the extensive research indicating that both microbial diversity and inflammation can be modulated through diet, the potential of a therapeutic diet for IBD is plausible. Yet without expert guidance patients can put themselves at high risk of unnecessary dietary restriction. As such, healthcare professionals should be familiar with the evidence behind popular therapeutic diets in order to provide sound education and eliminate misconceptions.
Gluten-Free Diet
Gluten is the general name for the complex proteins glutenin and gliadin present in most carbohydrate foods, such as wheat, rye and barley.
For individuals with Coeliac disease, the consumption of gluten is associated with symptoms of bloating, diarrhoea, abdominal pain and fatigue. In these patients, gluten peptides trigger an abnormal immune response that causes intestinal inflammation and damage.
Given the similarities between IBD and coeliac disease, there was early interest in whether gluten was contributing to the gastrointestinal inflammation identified in IBD and whether a gluten-free diet (GFD) could be an appropriate therapeutic diet.
Despite patients with IBD self-reporting improvements in clinical symptoms following dietary gluten elimination, to date there has been no association between the intake of gluten and IBD progression. By contrast, research has shown that the unnecessary removal of gluten may have a negative impact on microbial diversity which may have a negative impact on gastrointestinal health. Palma et al found that when healthy subjects trialled a GFD, the microbial implications imitated those evident in the active phase of IBD; a reduction in beneficial bacterial and an increase in opportunistic bacteria populations. In addition, research into the nutritional quality of gluten-free products consistently shows lower protein content with high fat and salt content compared to their equivalent gluten-containing products.
It is likely that self-reported improvements are a result of changes in diet quality. For example, the benefits arise from eliminating refined carbohydrate grains rather than the removal of gluten itself. This hypothesis is supported by the well-established association between a diet high in refined carbohydrates and both an increased presence of inflammatory markers and lower microbial diversity.
Therefore, there is insufficient evidence to recommend a GFD to individuals with IBD unless coeliac disease or a gluten intolerance has been diagnosed.
Mediterranean Diet & IBD
The gold standard for an anti-inflammatory diet is the Mediterranean diet (MD); heavy on vegetables, whole grains, olive oil; moderate on fish and red wine and light on red meat and processed foods.
MD has been shown to prevent the onset of dysbiosis by promoting microbial diversity and enriching beneficial bacteria, which support the mucosal barrier function and reduce intestinal inflammation. In patients with IBD, MD adherence has been associated with decreased inflammatory markers such as tumour necrosis factor (TNF) and interleukins-6.
Despite there being limited research, the MD has been shown to reduce symptoms and improve quality of life in patients with IBD. When compared with other therapeutic diets, MD stands out as the preferred dietary intervention, based on clinical outcomes, ease of following and the other health benefits associated with MD.
While more research is required, the MD can be recommended as a supportive dietary intervention to reduce disease markers and potentially relieve symptoms for patients with IBD. This advice is appropriate for IBD patients during remission and low symptom states, however during flares these patients may need to alter their diet texture and composition.
RECOMMENDATIONS
Although there is limited data from well-designed clinical trials to inform the routine use of any particular diet for treatment of IBD, it has been well-documented that patients with IBD are at higher risk of nutrient deficiencies and are more likely to avoid specific foods because of misconceived beliefs that specific foods will cause gastrointestinal symptoms.
As such patients should be gently discouraged from trialling any restrictive diets and dietary education should emphasise the importance of following a nutritionally adequate dietary pattern, such as MD, to promote and support long-term health.
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