Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is a disorder that involves abdominal pain and cramping, as well as changes in bowel movements. IBS is a functional bowel disorder with a prevalence of 10%–15% in Europe and North America, 15.9% in China, and 33% in Nigeria . There is a greater prevalence in women. A diagnosis of IBS is based on Rome III criteria that includes abdominal pain or discomfort as well as altered bowel patterns . There are three IBS subtypes that include IBS-C (constipation), IBS-D (diarrhea), and IBS-M (mixed constipation and diarrhea) [2,3]. Typically, the diagnosis is made after other diagnoses such as celiac disease and inflammatory bowel disease that have been ruled out but pain and symptoms continue [4,5].
IBS presentation of symptoms and their severity greatly varies from patient to patient. The symptoms include constipation, diarrhea, abdominal pain, bloating, gas, urgency, heartburn, and acid reflux, often without a known abnormal pathology [6,7]. Patients also report that overtime, symptoms can change and cross subgroups such as initially being IBS-C and constipation predominant to IBS-M that would also include diarrhea . Bloating, defined as the sensation of abdominal fullness and distention, resulting in an increase in abdominal girth, has been reported by more than 80% of patients with IBS; however, it is not reported by all . Symptoms also differ by gender with females reporting abdominal pain and constipation more often than males who report diarrhea . In the United States, 5.9 million prescriptions annually are written for the treatment of IBS symptoms, with direct and indirect costs exceeding 20 billion dollars, including missed work and increased physician visits. [5,7]. Therefore, treatment requires an individualized approach.
PATHOPHYSIOLOGY OF IRRITABLE BOWEL SYNDROME
It is thought that several separate gastrointestinal disorders may be universally called IBS, which accounts for the differences observed in symptoms, etiology, and pathophysiology [5,10].In the past, physicians treating IBS focused on abnormalities in GI motility, visceral sensation, brain–gut interactions, and psychosocial factors; however, none of these modalities accounted for symptoms in all IBS patients . Additional research has shown that an altered gut immune activation, increased levels of intestinal permeability, and the intestinal and colonic microenvironment differ in patients with IBS compared to controls that may be a consideration in the treatment provided [5,10,12,13].
MANAGEMENT OF IRRITABLE BOWEL SYNDROME
Management of IBS initially may be to utilize over-the-counter medications to resolve diarrhea or constipation, although this is most often when full testing has not been done and is early in the diagnostic process . This includes the use of antidiarrheals, probiotics, and antispasmodics for diarrhea, and the use of fiber supplements and laxatives for constipation . If symptoms readily resolve and do not return, then, no further action is required. However, in many IBS patients, symptoms have been present from months to years and diagnosis has been hard to determine. In patients such as these, management of symptoms with a specialized nutrition program, is now being used as the first line of treatment .
The majority of patients with IBS report that food triggers symptoms; up to 90% restrict one or more type of food to help alleviate symptoms and symptom severity . Food intolerances and food sensitivity are frequently reported in patients with IBS . Through assessment of the commonly reported food intolerances, it was originally hypothesized that certain categories of foods cause an increase in susceptibility to Crohn’s disease .This supposition further extended into the role of these food components in functional bowel disorders such as IBS. Food that are high in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (or FODMAPs) are carbohydrates that are poorly absorbed by the small intestine, are molecularly small and osmotically active, and are rapidly fermented by bacteria [10,17]. These GI effects from consumption of high FODMAP foods result in an excessive intestinal fluid, increased gas production, bowel distention, and bloating resulting in abdominal pain and diarrhea [10,17]. The fermentation rate of these molecules is determined by the length of the carbohydrate chain, with high FODMAP foods being fermented at a faster rate . Foods can be classified as those with excess fructose (like some fruits), lactose-containing oligosaccharides, and polyol-containing foods. Consuming a diet high in FODMAPs favors the production of hydrogen over other gases such as methane, which has been shown to cause gastrointestinal distress .
THE FODMAP ELIMINATION DIET
The FODMAP diet is an elimination of all high FODMAP foods for a specific period of time and then a gradual reintroduction of eliminated, higher FODMAP foods to determine tolerance based on symptoms [10,14,18]. Foods high in FODMAPs that are more likely to cause GI distress are listed in Table 5.1. The elimination of all high FODMAP foods followed by reintroduction of these foods allows an individual to determine what specific foods cause the most distress, allowing for an individualized approach. It is important to note that the foods noted as high FODMAP seem to “change” based on the resources used. This is because research into the FODMAP content of foods in ongoing and therefore data will change [7,10]. The Monash FODMAP app is an excellent tool for determining high FODMAP foods (http://www.med.monash.edu.au/cecs/gastro/fodmap/iphone-app.html).
OLIGOSACCHARIDES (FRUCTANS OR GALACTANS)
Fructans are linear-branched fructose polymers and naturally occurring carbohydrates that are found in onions, garlic, artichokes, some fruits, and cereals . Wheat is one of the main sources of fructans in the American diet. Inulin and fructo-oligosaccharides (FOS) are commercially used as fiber additives . Fructans, especially in patients with IBS, are not absorbed in the intestine and as a result, reach the colon undigested and are fermented into gas and short-chain fatty acids (SCFA) [15,19]. Galactans are naturally found in legumes, lentils, chickpeas, red kidney beans, and function similar to fructans . Humans lack the enzyme needed to digest and absorb galactans so that they are rapidly fermented in the small intestine and produce gas . In the absence of IBS or GI compromise, fructans provide a readily available source of fiber to many people and therefore, when these are eliminated, other sources of fiber should be encouraged. Soluble fibers and those derived from psyllium husk are well tolerated in IBS. In addition, the modification of the fructan intake specifically affects prebiotic foods (including FOS) and therefore changes the microbiota .It is not clear if that is a negative effect.