Low-FODMAP Diet for Treatment of Irritable Bowel Syndrome Suma Magge, MD, and Anthony Lembo, MD Dr. Magge is a Fellow and Dr. Lembo Abstract: Functional bowel disorders, including irritable bowel is an Associate Professor of Medicine syndrome (IBS), are common disorders that have a significant in the Division of Gastroenterology at impact on patients’ quality of life. These disorders present major Beth Israel Deaconess Medical Center in challenges to healthcare providers, as few effective medical thera- Boston, Massachusetts. pies are currently available. Recently, there has been increasing Address correspondence to: interest in dietary therapies for IBS, particularly a diet low in Dr. Anthony Lembo fermentable oligosaccharides, disaccharides, monosaccharides, Division of Gastroenterology and polyols (FODMAPs). Since ingestion of FODMAPs increases Beth Israel Deaconess Medical Center the delivery of readily fermentable substrates and water to the Rabb Rose 1 distal small intestine and colon—which results in luminal disten- 330 Brookline Avenue Boston, MA 02215; tion and gas—the reduction of FODMAPs in a patient’s diet may Tel: 617-667-2138; improve functional gastrointestinal symptoms. This paper will Fax: 617-667-1171; review the pathophysiology of IBS and the role of FODMAPs for E-mail: [email protected] the treatment of this condition. rritable bowel syndrome (IBS) is a chronic, often disabling, func- tional disorder characterized by abdominal pain and changes in bowel habits.1 The prevalence of IBS in the US general population Ivaries 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 fermen- tation, and sugar malabsorption, all of which lead to increased gas production and luminal distention.7 The use of elimination diets for Keywords the treatment of IBS has yielded conflicting results, although this Irritable bowel syndrome, FODMAPs, small treatment option has been slightly more successful in IBS patients 8 intestinal bacterial overgrowth, food allergy, food who have diarrhea. However, elimination diets can result in dietary intolerance, hydrogen breath testing restrictions that can be burdensome to patients and can potentially Gastroenterology & Hepatology Volume 8, Issue 11 November 2012 739 M a gg e a N d L e M b o compromise their nutritional health. In addition, there is bloating, flatus, and diarrhea. Patients with more a lack of randomized controlled data that show a symp- severe disease can experience malabsorption due to the tomatic benefit with elimination diets.9 inflammatory effects of bacteria on small bowel mucosa. Recently, interest has focused on diets that reduce For example, macrocytic anemia can result from intake of poorly absorbed, small molecule–sized carbohy- vitamin B12 deficiency, while hypocalcemia can result drates. These types of carbohydrates are fermented by intes- from vitamin D deficiency.13 Children with SIBO are tinal bacteria, which produces gas and osmotically active susceptible to more severe disease; they may develop byproducts, causing an increase in fluid in the intestines. malnutrition and/or steatorrhea and may have difficulty The acronym FODMAPs (which stands for fermentable maintaining their weight and growth.14 oligosaccharides, disaccharides, monosaccharides, and SIBO can be diagnosed via several methods.15 The polyols) was developed to describe these poorly absorbed, gold standard for diagnosis is a jejunal aspirate with at least short-chain carbohydrates.10 Observational studies have 105 CFU/mL of bacteria. Several endoscopic techniques shown that the restriction of FODMAPs in the diet alle- can be used to sample the contents of the small bowel. viates gastrointestinal symptoms in patients with IBS. Classically, the jejunum is intubated under fluoroscopic Therefore, a low-FODMAP diet represents an opportunity guidance, but this method has fallen out of practice due for treatment in these patients. The aim of this paper is to to its invasive nature and the possibility for contamination review the pathophysiology of IBS, the current evidence- of the aspirate by Gram-positive organisms in the oropha- based literature in this area, and the application of a low- ryngeal flora. The reproducibility of the culture technique FODMAP diet for treatment of IBS patients. The role of has also been shown to be suboptimal (<38% vs 92% for diet in functional bowel disorders such as IBS has become breath testing). In addition, the criteria commonly used a popular area of interest, given the frequent association of to diagnose SIBO (>105 CFU/mL of bacteria)—which symptoms and foods, as well as the limited availability of were proposed by Reid and colleagues—have not been effective and safe pharmacologic therapies. validated.16 A systematic review by Khoshini and associates found that there was no adequately validated diagnostic test Pathophysiology for SIBO.12 The researchers also suggested that there was a lack of evidence to justify the use of culture as the gold Small Intestinal Bacterial Overgrowth in Irritable Bowel standard test for SIBO.12 Syndrome Patients Given these limitations, noninvasive and less expen- Small intestinal bacterial overgrowth (SIBO) is the sive tests such as breath testing are more commonly used abnormal growth in the small intestine of bacteria that for diagnosing SIBO. Breath testing is based on the are normally found only in the colon. The stomach and premise that bacteria are the sole producers of intestinal proximal small bowel (the duodenum and jejunum) nor- hydrogen, some of which is exhaled. Therefore, testing mally contain few bacteria (usually <104 colony-forming can measure the amount of hydrogen gas that is pro- units per milliliter [CFU/mL]). In contrast, the terminal duced when a fixed dose of a substrate (ie, a carbohy- ileum has significantly more anaerobic bacteria (as high as drate) is encountered by bacteria in the bowel. The most 109 CFU/mL), and the colon has even more bacteria commonly used substrates are glucose and lactulose. (as high as 1012 CFU/mL).11 In SIBO patients, the Glucose is absorbed in the first 3 ft of the small intestine; concentration of bacterial flora increases proximally therefore, it is only capable of detecting SIBO in the (>105 CFU/mL).12 proximal small bowel. An increase of at least 12 parts Gastric acid and small bowel peristalsis are important per million at 120 minutes after ingestion is generally mechanisms for the prevention of SIBO. Low gastric pH considered to be a positive test result for SIBO.11 In con- is an effective antimicrobial agent, as it kills bacteria and trast, lactulose is a nonabsorbable carbohydrate that is suppresses their growth. Likewise, intestinal motility (via eventually fermented by colonic bacteria. The diagnosis the migrating motor complex) has a cleansing effect and of SIBO via the lactulose breath hydrogen test (LBHT) prevents excess bacteria from colonizing the small bowel. is based on the following criteria: The first peak is caused Conditions that affect these mechanisms—such as sclero- by the production of gas due to bacterial overgrowth in derma, hypothyroidism, diabetes, and potentially IBS—can the small bowel, and the second peak results from the result in SIBO.11 SIBO secondary to impaired motility has action of colonic bacteria on lactulose.17 The LBHT has different effects than IBS, in which the gut has no structural a higher specificity compared to the glucose hydrogen or functional disruptions. breath test (~86% vs ~80%, respectively), but the for- SIBO can cause a wide range of symptoms, includ- mer has lower sensitivity and accuracy.18 ing those consistent with IBS. Commonly, patients Many, but not all, studies have shown that patients with SIBO experience nausea, abdominal cramping, with IBS have abnormal LBHT results, which suggests that 740 Gastroenterology & Hepatology Volume 8, Issue 11 November 2012 L o w - F o d M a P d I e t F o r t r e a t M e N t o F I b S SIBO may be involved in the pathogenesis of IBS. This ity of this test in IBS patients is dubious.21 In a study of association was first reported by Pimentel and coworkers 88 patients with gastrointestinal symptoms that were in 2003.19 In this study of 111 IBS patients, approximately thought to be caused by a food allergy, only 15 patients 84% had an abnormal LBHT result compared to only had reproducible symptoms in a double-blind, placebo- 20% of healthy subjects (n=15). Patients who received controlled (DBPC) trial, and none of the patients had a neomycin had a 35% improvement in symptoms com- positive skin-prick test result or a positive radioallergo- pared to a 11.4% improvement in patients who received sorbent test score for the food that reproduced the symp- placebo. Importantly, normalization of LBHT results toms.22 In a study of 81 patients with IBS symptoms that was associated with the use