Food intolerance and Crohn's disease

Does evidence exist to include dietary therapy in the treatment of Crohn's disease?

Prescription drugs and surgery are two common medical therapies for Crohn's disease (CD), an inflammatory bowel disease that affects the GI tract. Unfortunately, certain drugs can cause serious side effects, and surgeries must often be repeated. No diet has been established to alleviate the pain and suffering of CD patients. This is curious given the fact that a higher prevalence of food sensitivities exist in this population of patients, and enteral nutrition is not only the first-line of therapy in Japan, but a known research method used to place the majority of CD patients into remission. Although not all patients respond equally to diet, many simply remove symptom-provoking foods, such as dairy, wheat, corn and certain fruits and vegetables. We suggest assisting these patients in their self-assessment of irritating and symptom-provoking foods by educating them in the use of a food-symptom diary followed by a customized elimination diet trialed for 2-4 weeks to determine if there is any benefit to the individual patient.

Genes, diet and inflammatory bowel disease

Inflammatory bowel disease (IBD) arises in part from a genetic predisposition, through the inheritance of a number of contributory genetic polymorphisms. These variant forms of genes may be associated with an abnormal response to normal luminal bacteria. A consistent observation across most populations is that any of three polymorphisms of the Caspase-activated recruitment domain (CARD15) gene are more prevalent in IBD patients as compared with unaffected controls. Similar aberrant responses to bacteria are associated with variants in Autophagy-related 16-like 1 (ATG16L1) and human defensin (HBD-2, -3 and -4) genes. The defective bacterial signal in turn leads to an excessive immune response, presenting as chronic gut inflammation in susceptible individuals. Inconsistent population reports implicate the major histocompatability complex (MHC), that encodes a number of human leukocyte antigens (HLA), MHC class I chain-related gene A (MICA) or cytokines, such as tumour necrosis factor-alpha (TNF-alpha). Toll-like receptors encoded by the TLR4 or TLR9 genes may also play a role. Recent whole genome scans suggest that a rare variant in the interleukin-23 receptor (IL23R) gene may actually protect against IBD. Other implicated genes may affect mucosal cell polarity (Drosophila discs large homologue 5, DLG5) or mucosal transporter function (sodium dependent organic cation transporters, SLC22A4 and SLC22A5). A variant in ABCB1 (ATP-binding cassette subfamily B member 1) may be especially associated with increased risk of UC. While pharmacogenetics is increasingly being used to predict and optimise clinical response to therapy, nutrigenetics may have even greater potential. In many cases, IBD can be controlled through prescribing an elemental diet, which appears to act through modulating cytokine response and changing the gut microbiota. More generally, no single group of dietary items is beneficial or detrimental to all patients, and elimination diets have been used to individualise dietary requirements. However, recognising the nature of the genes involved may suggest a more strategic approach. Pro- or prebiotics will directly influence the microbial flora, while immunonutrition, including omega-3 fatty acids and certain polyphenols, may reduce the symptoms of gut inflammation. The expression of gut transporters may be modulated through various herbal remedies including green tea polyphenols. Such approaches would require that the gene of interest is functioning normally, other than its expression being up or down-regulated. However, new approaches are being developed to overcome the effects of polymorphisms that affect the function of a gene. A combination of human correlation studies with experimental models could provide a rational strategy for optimising nutrigenetic approaches to IBD.

Review article: the dietary management of Crohn's disease

Enteral feeding has been shown to be as effective as primary therapy for Crohn's disease, but it requires high patient motivation, may be unpalatable and is expensive. However, in adolescents with growth failure and when corticosteroid therapy is contra-indicated or has failed, it may become the treatment of choice. Furthermore, dietary therapy allows circumvention of the adverse side-effects of repeated courses of steroids. A number of different hypotheses have been proposed to explain the effect of enteral feeds but none has reached universal acceptance. Prospective trials suggest that the exclusion of whole protein is not necessary. Comparison of feeds with differing composition suggests that a low fat content increases efficacy and various explanations have been offered. The reduction of colonic bacterial load may also be important. Because symptoms of Crohn's disease may be provoked by eating, there is a risk of falsely attributing symptoms to specific foodstuffs. However, in many individuals foods can be identified which affect disease activity, and their exclusion leads to prolongation of disease remission. Dietetic supervision during food testing is important to avoid detrimental effects on nutrient and micronutrient intake.

Cellular mechanisms underlying the increased duodenal iron absorption in rats in response to phenylhydrazine-induced haemolytic anaemia

Haemolytic anaemia induced by phenylhydrazine (PZ) promotes iron absorption across rat small intestine. This present study investigates the role of the brush border potential difference (Vm) and mucosal reducing activity in the response. In addition, quantitative autoradiography was used to assess PZ-induced changes in the villus localization of brush border iron uptake. Iron transfer from duodenum to blood was increased significantly 5 days after treatment with PZ. Autoradiography showed that most brush border iron uptake occurred at the upper villus region and the maximal rate was increased fourfold by PZ. Duodenal villus length was increased in PZ-treated rats. PZ treatment did not influence mucosal reducing activity but Vm, measured using duodenal sheets, increased from -50 to -57 mV (P < 0.001) and this was due to a reduced brush border sodium permeability. Thus, an expanded absorptive surface and an enhanced electrical driving force for iron uptake across the duodenal brush border are important adaptations for increased iron absorption in PZ-induced haemolytic anaemia.