Low-FODMAP Diet for Treatment of Irritable Bowel Syndrome

摘要

Functional bowel disorders, including irritable bowel syndrome (IBS), are common disorders that have a significant impact on patients’ quality of life. These disorders present major challenges to healthcare providers, as few effective medical therapies are currently available. Recently, there has been increasing interest in dietary therapies for IBS, particularly a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs). Since ingestion of FODMAPs increases the delivery of readily fermentable substrates and water to the distal small intestine and colon—which results in luminal distention and gas—the reduction of FODMAPs in a patient’s diet may improve functional gastrointestinal symptoms. This paper will review the pathophysiology of IBS and the role of FODMAPs for the treatment of this condition. Irritable bowel syndrome (IBS) is a chronic, often disabling, functional disorder characterized by abdominal pain and changes in bowel habits.1 The prevalence of IBS in the US general population varies between 8% and 20% depending on diagnostic criteria and the population that is evaluated.2 Most studies report a higher prevalence of IBS in women than men.3 The average medical expenditure for IBS in the United States is estimated to be $1.35 billion in direct costs and $205 million in indirect costs.4 IBS also accounts for almost half of all visits to gastroenterologists. The pathophysiology of IBS is incompletely understood, and treatment options are limited, partly due to the heterogeneity of the IBS population.5 Nearly two thirds of IBS patients report that their symptoms are related to food.6 The pathogenic mechanism by which food induces IBS symptoms remains unclear, but it includes visceral hypersensitivity, altered motility, abnormal colonic fermentation, and sugar malabsorption, all of which lead to increased gas production and luminal distention.7 The use of elimination diets for the treatment of IBS has yielded conflicting results, although this treatment option has been slightly more successful in IBS patients who have diarrhea.8 However, elimination diets can result in dietary restrictions that can be burdensome to patients and can potentially compromise their nutritional health. In addition, there is a lack of randomized controlled data that show a symptomatic benefit with elimination diets.9 Recently, interest has focused on diets that reduce intake of poorly absorbed, small molecule–sized carbohydrates. These types of carbohydrates are fermented by intestinal bacteria, which produces gas and osmotically active byproducts, causing an increase in fluid in the intestines. The acronym FODMAPs (which stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) was developed to describe these poorly absorbed, short-chain carbohydrates.10 Observational studies have shown that the restriction of FODMAPs in the diet alleviates gastrointestinal symptoms in patients with IBS. Therefore, a low-FODMAP diet represents an opportunity for treatment in these patients. The aim of this paper is to review the pathophysiology of IBS, the current evidence-based literature in this area, and the application of a low-FODMAP diet for treatment of IBS patients. The role of diet in functional bowel disorders such as IBS has become a popular area of interest, given the frequent association of symptoms and foods, as well as the limited availability of effective and safe pharmacologic therapies. Pathophysiology Small Intestinal Bacterial Overgrowth in Irritable Bowel Syndrome Patients Small intestinal bacterial overgrowth (SIBO) is the abnormal growth in the small intestine of bacteria that are normally found only in the colon. The stomach and proximal small bowel (the duodenum and jejunum) normally contain few bacteria (usually <104 colony-forming units per milliliter [CFU/mL]). In contrast, the terminal ileum has significantly more anaerobic bacteria (as high as 109 CFU/mL), and the