Food and Functional Bowel DiseaseFood Components and Irritable Bowel Syndrome
Section snippets
Food Intake and Functional Bowel Symptoms
A large proportion of patients with IBS associate food intake with the development of abdominal symptoms.7 The relationship between food and symptoms is difficult to determine due to the complexity of food composition, the multiple putative mechanisms by which foods or food components affect the gut8 and induce symptoms, and difficulties in identifying these mechanisms in each individual.
There are many mechanisms by which food might act on the gut to cause symptoms of IBS. The first is the
Patient-Initiated Dietary Changes
Patients with IBS often express an intense interest in food choice and attempt to identify foods that induce symptoms. For example, food items were limited or excluded from diets of 62% of patients in a study of IBS in Norway; 1 in 8 had changed their diets considerably, which presumably reduced their symptoms.3 Unfortunately, the accuracy of this method of identifying food culprits is limited,15 and there are substantial nutritional risks associated with patient-initiated strategies.
Conceptual Diets
Multiple
Elimination and Rechallenge Diets
Elimination and rechallenge diets require patients to follow a highly restrictive elimination diet for 1−4 weeks. Patients who experience a concomitant reduction in symptoms reintroduce foods, one at a time, in a blinded or open manner to determine which foods induce symptoms. Foods are selected for elimination based on experience. Enthusiasm for this technique is tempered by the poor quality of studies conducted in this area. The studies have been criticized because of their poorly defined
Carbohydrates
Carbohydrates of relevance to IBS comprise those that are slowly absorbed or cannot be digested in the small intestine. These are generally referred to, slightly erroneously, as indigestible carbohydrates. This term applies to oligosaccharides and nonstarch polysaccharides (the small intestine does not produce hydrolases that release monosaccharides), as well as fructose and polyols, which are slowly absorbed from the small intestine rather than digested. Carbohydrates can be grouped according
Proteins
Most interest in dietary proteins relate to their potential to induce symptoms by a variety of mechanisms, with immune-mediated or injurious processes usually implicated. However, identification of the specific culprit proteins has been challenging. The dietary protein that has attracted the most attention is gluten, which provides an excellent model for addressing issues and challenges in studies of protein sensitivity.
Gluten is headline news for several reasons. It is a dietary protein that
Wheat Protein vs Fermentable Oligo-, Di-, and Mono-Saccharides and Polyols
The separate effects of wheat proteins and FODMAP content were evaluated in a series of randomized controlled trials of highly selected patients who fulfilled the criteria for NCGS and had normal duodenal histopathology (on gluten-containing diets) and/or HLA haplotypes that excluded celiac disease. Patients were placed on diets with FODMAP-depleted wheat protein. Although a pilot parallel-group study found that wheat protein induced more symptoms than placebo supplements,53 a subsequent study
Lipids
Administration of lipids into the duodenum of healthy volunteers can increase perception of intestinal stimuli, slow small intestinal transit, enhance colonic motility, and increase visceral sensitivity in the rectum, as reviewed in Feinle-Bisset and Azpiroz.59 These responses can be largely mediated by cholecystokinin, but other gut hormones are also likely to be involved. In patients with IBS, some gut responses to fat are exaggerated and might be associated with symptom genesis, such as a
Bioactive Food Chemicals
The human GI tract is exposed to a soup of bioactive chemicals. They can be naturally occurring in plants (such as salicylates, amines, and glutamates) or added to processed foods as preservatives, humectants, and coloring or flavoring agents (such as monosodium glutamate, tartrazine, and sodium benzoate). These chemicals have the potential to act via specific receptors10 or directly on cells such as mast cells11 (see Figure 3).
Bioactive food chemicals might be used therapeutically. For example
Risks of Dietary Manipulation
Health professionals advising dietary change or managing patients undertaking dietary change should be aware of risks associated with these strategies. Nutritional inadequacy is a particular problem associated with patient-initiated strategies, as patients can blame innocent-bystander foods, resulting in over-restriction. In a Norwegian study, 12% of patients with IBS were considered to have a nutritionally inadequate diet, due to exclusions.7 Furthermore, many patients who believe they have
Conclusions
We are beginning to understand how foods contribute to the pathogenesis of GI symptoms. Findings have led to a surge of interest in the use of diet to control symptoms. The focus has shifted from whole-food therapeutic approaches to the manipulation of food components, which provides a more scientifically rational basis for dietary manipulation and increases our ability to keep up with constant changes in our food supply. Health care providers need to consider dietary aspects of therapy for
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Conflicts of interest These authors disclose the following: Peter R. Gibson receives royalties from sales of an information/cookbook that he coauthored on the low FODMAP diet. Peter R Gibson, Jane Varney, and Jane G Muir are actively involved with, but receive no personal income from, the Monash University Low FODMAP Diet App. Net funds generated from sales of the App are invested into further dietary research at Monash University and the Department of Gastroenterology. The remaining author discloses no conflicts.
Funding The work presented was supported in part by research grants from the National Health and Medical Research Council and Australian Research Council, and from Postgraduate Research Scholarships from Monash University.