Irritable Bowel Syndrome: What Kind of Fiber, What Kind of Oils?

Desiree Lie, MD, MSEd


February 12, 2009


IBS is a functional gastrointestinal disorder characterized by recurrent abdominal pain and a change in bowel habit.[1] It has a community prevalence estimated at 5% to 20%, according to surveys.[2,3,4,5] IBS is considered a relapsing, remitting condition that presents mainly to primary care physicians. The diagnosis is made on the basis of clinical criteria (eg, the Rome criteria) and by the exclusion of other bowel pathology.[1,5,6,7]

The physiologic mechanism that causes IBS symptoms is believed to be altered gut motility associated with smooth muscle spasm, visceral hypersensitivity, and abnormalities of pain processing.[1] Impaired (accelerated) gut transit time has also been examined as a possible mechanism.[6]

The signs and symptoms of IBS can vary from person to person. Among the most common symptoms are abdominal pain, cramping, bloating, flatulence, diarrhea or constipation, and mucus in the stool. A diagnosis of IBS should be considered if a patient has abdominal pain that is relieved by defecation as well as by at least 2 of the other symptoms of IBS. Because IBS is a diagnosis of exclusion, laboratory tests (ie, full blood cell count, erythrocyte sedimentation rate, antibody testing for celiac disease) are used to rule out other diagnoses.

When assessing the severity of IBS symptoms, the Bristol Stool Form Scale[8] is a good tool by which to visually gauge stool quality and quantity. In addition, the patient should be asked about incidences of incomplete evacuation, rectal hypersensitivity, and stooling urgency or incontinence to assess the effect of IBS on quality of life and to facilitate best management.

The goals of treatment are symptom control and the regular production of soft, well-formed stools (type 4 on the Bristol Stool Form Scale). Guidelines for the management of IBS are available from the American Gastroenterological Association,[7] the British Society for Gastroenterology,[9] and the United Kingdom digestive diseases group, CORE.[10] The primary strategies are dietary modification, lifestyle change (ie, increased physical activity), pharmacotherapy (ie, antispasmodics, antidiarrheals, and antidepressants), and behavioral and psychological interventions. The National Institute for Health and Clinical Excellence also recommends alternative and complementary therapies including cognitive behavioral therapy, hypnotherapy, and biofeedback.[8]

Because lifestyle changes, such as physical activity and diet modification, can significantly affect symptomatic IBS, the primary care physician should inform patients about the value of self-help in effectively managing their symptoms. IBS is a difficult disease to treat, but lifestyle changes coupled with symptom-targeted medication can result in good symptom control.

The pharmacologic options in the management of IBS include bulking agents, antispasmodics, peppermint oil, and antidepressant agents. A number of systematic reviews and meta-analyses have examined the relative efficacy of different treatments for IBS.[11,12,13,14,15] However, most clinical studies that assess treatment efficacy are of short duration and focus on subjective symptoms.

The use of bulking agents, such as fiber, may increase bowel transit time and improve symptoms. Among the different bulking agents studied, nonsoluble fibers, such as bran, have not been found to be beneficial; in fact, a large intake of high-fiber foods, such as cereals high in brain and whole grains, should be avoided.[8,16] However, the use of soluble fibers, such as ispaghula powder or oats, should be encouraged.[16,17] The most recent systematic review that examines the role of different fibers on IBS symptoms found that ispaghula husk had the greatest benefit among fiber supplements, having a number needed to treat (NNT) of 6, as compared with bran or other fibers (not psyllium), with NNTs higher than 10.[18] The dosages of ispaghula husk used in the studies reviewed in the meta-analysis ranged from 2 to 3 sachets daily.

Antispasmodic agents relieve IBS symptoms by acting on smooth muscle to improve gut motility. Among antispasmodic agents, hyoscine had the greatest benefit among those examined, which included otilonium, trimebutine, cimetropium, dicycloverine, mebeverine, and pirenzipine.[19] Hyoscine, an antimuscurinic agent extracted from the cork wood tree, is available over the counter. Antispasmodics are effective in the treatment of IBS symptoms, having an overall NNT of 5 in studies involving primarily constipation-predominant IBS.[18]

Peppermint oil, a hybrid product of spearmint and water mint that is available in a variety of forms, is a safe and efficacious treatment for IBS. It is believed to reduce gastrointestinal smooth muscle motility by acting as a calcium channel antagonist. Doses used in trials of IBS include 1 to 2 enteric-coated capsules (0.2 to 0.4 mL of peppermint oil or 187-374 g of peppermint oil in a thixotropic gel) 3 times daily at 15 to 30 minutes before meals; 180 to 200 mg enteric-coated peppermint oil; and 225 mg peppermint oil taken twice daily. In a meta-analysis that compared the benefits of fiber, antispasmodics, and peppermint oil, peppermint oil turned out to be the most efficacious treatment,[18] having an NNT of 2.5 in 4 studies that ranged in duration from 4 weeks to 3 months and that included patients with diarrhea-predominant IBS as well as patients with constipation-predominant IBS.[20,21,22] The dosages of peppermint oil used in the studies ranged from 187 to 225 mg 2 to 3 times daily. Adverse effects are rare -- the most common complaint with oral peppermint oil use is heartburn followed by perianal burning and nausea and vomiting.[23]

Antidepressants in low analgesic doses have also been recommended for IBS. Generally, tricyclic anitdepressants are the first choice. However, if they prove to be ineffective, SSRIs may prove beneficial.[8]

Alternative medicine options including acupuncture, Chinese herbals, and reflexology have been used as adjunctive therapy in the management of IBS, but there is no evidence to support their efficacy. Limited evidence indicates that probiotics, relaxation, and biofeedback may be useful in the management of IBS, but more research is needed to define the benefits of these modalities.[8]

Response to Case 1

Mr. X has adopted a dietary strategy for IBS that is not of proven efficacy and that may, in fact, worsen some of his symptoms. Insoluble fiber (such as bran) and lactulose are not recommended for constipation management in IBS. Instead, a soluble fiber such as ispaghula husk, 2 to 3 sachets taken daily, may be of benefit. Peppermint oil is worth adding for at least 1 to 2 months to control bloating and abdominal pain. Referral to a dietician to identify specific triggers for his IBS episodes may be helpful. Behavioral cognitive therapy to better deal with work stress may be indicated, if he is open to the intervention. With a history of depression, he is at risk for a recurrence and a low-dose antidepressant for analgesia may be indicated at this stage. Ideally, Mr. Y should return for a follow-up visit within 1 month to allow his physician to monitor his general symptoms, evaluate the effect of lifestyle modifications, and assess for depression and alarm symptoms.

Response to Case 2

Mrs. Y appears to have intractable symptoms that interfere with her lifestyle and work. Loperamide is a first-choice antidiarrheal for diarrhea-predominant IBS. If she wishes to use fiber, a soluble fiber should be recommended. Anxiolytics have no proven efficacy for IBS symptoms. She should be advised to take peppermint oil 3 times daily, and if this does not control the bloating and abdominal pain, an antispasmodic such as hyoscine, which is available over the counter, could be considered. Increasing physical activity through simple exercises or walking is likely to improve her symptoms. In addition, she might consider using either relaxation or biofeedback as a way to prevent exacerbation or recurrence of symptoms. Mrs. Y is also a candidate for an antidepressant, which should be used in an analgesic dose for pain control. A follow-up visit is recommended to allow the physician to monitor her progress and assess for "red flag" symptoms.

Clinical Pearls

  • The diagnosis of IBS is made on the basis of clinical criteria and the exclusion of other diagnoses;

  • IBS may present as abdominal pain associated with either frequent diarrhea or frequent constipation;

  • Multiple practice guidelines are available for management of IBS, and the recommended treatment strategies include self-care (diet and exercise), behavioral, and pharmacologic interventions;

  • Soluble fiber and dietary prudence are recommended for stool management; and

  • Peppermint oil has greater efficacy than antispasmodics for bloating and abdominal pain.


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