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What Does the Newest AGA Guidance Provide on Diet and Irritable Bowel Syndrome?

  • Authors: News Author: Laird Harrison; CME Author: Charles P. Vega, MD
  • CME / ABIM MOC / CE Released: 6/3/2022
  • Valid for credit through: 6/3/2023, 11:59 PM EST
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Target Audience and Goal Statement

This activity is intended for primary care providers, gastroenterologists, nurses, physician assistants, pharmacists, and other members of the healthcare team who care for patients with irritable bowel syndrome (IBS).

The goal of this activity is that learners will be able to evaluate clinical guidelines for the management of IBS through diet.

Upon completion of this activity, participants will:

  • Assess how diet and medical therapy can affect IBS
  • Evaluate clinical guidelines for the management of IBS through diet
  • Outline implications for the healthcare team


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News Author

  • Laird Harrison

    Freelance writer, Medscape


    Disclosure: Laird Harrison has disclosed no relevant financial relationships.

CME Author

  • Charles P. Vega, MD

    Health Sciences Clinical Professor of Family Medicine
    University of California, Irvine School of Medicine


    Disclosure: Charles P. Vega, MD, has disclosed the following relevant financial relationships:
    Served as an advisor or consultant for: GlaxoSmithKline; Johnson & Johnson Pharmaceutical Research & Development, L.L.C.

Editor/Compliance Reviewer

  • Amanda Jett, PharmD, BCACP

    Associate Director, Accreditation and Compliance
    Medscape, LLC


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Nurse Planner

  • Stephanie Corder, ND, RN, CHCP

    Associate Director, Accreditation and Compliance
    Medscape, LLC


    Disclosure: Stephanie Corder, ND, RN, CHCP, has disclosed no relevant financial relationships.

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This activity has been peer reviewed and the reviewer has disclosed no relevant financial relationships.

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What Does the Newest AGA Guidance Provide on Diet and Irritable Bowel Syndrome?

Authors: News Author: Laird Harrison; CME Author: Charles P. Vega, MDFaculty and Disclosures

CME / ABIM MOC / CE Released: 6/3/2022

Valid for credit through: 6/3/2023, 11:59 PM EST


Clinical Context

Irritable bowel syndrome (IBS) is a common and challenging diagnosis for both patients and healthcare providers (HCPs); IBS is associated with worse quality of life and disability, yet there a few highly effective treatments for IBS. In fact, the authors of the current recommendations noted that fewer than half of patients with IBS respond to medical therapy, and the therapeutic gain of active treatment over placebo is limited to 7% to 15%.

Diet is an important part of IBS. More than 80% of patients with IBS state that their symptoms are related to meals. Carbohydrates are the macronutrient most often implicated in promoting IBS symptoms, and the group of carbohydrates known as low-fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) are particularly implicated in making IBS more severe.

Therefore, diet is an important part of the therapeutic plan for IBS. The current guideline by Chey and colleagues addresses best practices in the treatment of IBS with diet.

Study Synopsis and Perspective

Primary care providers and gastroenterologists who are treating patients with IBS should screen them for eating disorders before prescribing new diets, according to an expert panel of the American Gastroenterological Association (AGA).

"We're starting to identify disordered eating behaviors in patients with IBS, and it could affect their nutritional status," Lin Chang, vice-chief of digestive health at the University of California, Los Angeles, told Medscape Medical News.

Rather than new dietary restrictions, these patients should be referred to a registered dietitian nutritionist (RDN) and a mental health provider, said Chang, co-author of a new clinical practice update on the role of diet in IBS published this month in Gastroenterology.

"If you feel that somebody does have disordered eating, then you wouldn't put them on a restrictive diet or an elimination diet because they probably already have restricted a lot of foods," she said.

In addition to anorexia nervosa and bulimia nervosa, a particular consideration in patients with IBS is avoidant/restrictive food intake disorder (ARFID), in which patients avoid selected foods to the point of malnutrition or unhealthy weight loss.

The update provides a set of 8 questions that clinicians can use to screen their patients for disordered eating, including whether the patients have already changed their own diet, what emotions they feel at mealtime, and how much time they spend thinking about food and planning meals.

Restrictive diets also may not help someone who is at risk for malnutrition, is food insecure, is cognitively impaired, or is already not consuming much of the foods likely to cause symptoms, according to the update. It includes a Malnutrition Screening Tool.

First AGA Guidance on IBS and Diet

The clinical practice update is the first guidance that the AGA has provided on the subject of diet and IBS. It falls short of an official guideline because there was not enough research for a systematic review that grades the quality of the evidence, Chang said. The document uses the term "advice" instead of "recommendation."

Still, IBS is a common diagnosis, important studies have been published recently, and patients have shown increased interest in diet, making expert guidance timely, she said.

"This is a timely, informative piece that will be of great value to any healthcare provider who sees patients with IBS," said Brian Lacy, MD, PhD, a professor of medicine at the Mayo Clinic in Jacksonville, Florida, who was not involved in drafting the guidance.

Diet is a first-line treatment, although it should be combined with medication at least in patients with severe IBS, said Chang.

"There's been a significantly increased interest of dietary therapies that have been studied in more controlled trials for IBS, and also a lot of interest by patients," she said.

In addition, more dietitians are specializing in gastrointestinal disorders.

"They can spend a lot more time with patients and really go over their diet," she said. "The physician doesn't necessarily have time to go into that detail, nor the knowledge."

The clinical update calls for referral to an RDN when the patients have disordered eating and also when they are not able to make healthy changes in their diets on their own.

The update provides tips on the billing codes that physicians can use to increase the likelihood that an appointment with an RDN will be reimbursed by a health plan.

Also, the update says, restrictive diets should not go on indefinitely because they can cause malnutrition. If a diet does not seem to be working, the patient should switch to another diet or a different therapy altogether.

For example, more evidence supports the low-fermentable oligosaccharides, disaccharides, and monosaccharides and polyols (FODMAP) diet than any other diet for IBS, but these studies have shown that 4 to 6 weeks of the diet are enough to see whether the patient will respond. If a low-FODMAP diet seems to be working, the patient should gradually resume eating the FODMAP foods after the restriction phase, personalizing the diet to avoid only the foods that trigger symptoms in that patient.

The update notes evidence supporting 3 other diets: the traditional dietary advice of the National Institute of Health and Care Excellence (NICE) of the United Kingdom, a gluten-free diet, and the Mediterranean diet. Although all show some efficacy, the low-FODMAP diet worked at least slightly better in most head-to-head comparisons.

Patients with IBS with constipation may benefit from eating more soluble fiber, according to the update.

Preliminary evidence suggests that biomarkers may one day provide useful in determining which diet will most benefit which individual, the update says.

"Don't be surprised that in the next 1-3 years we review new testing (blood based) that may help identify food in individual patients that should be eliminated to improve IBS symptoms," said Lacy.

Chang reported financial relationships with Cosmo, Mauna Kea Technologies, and ModifyHealth. Lacy reported being on scientific advisory boards for Allakos, Ironwood, and Salix.

Gastroenterol. Published online March 22, 2022.[1]

Study Highlights

  • Candidates for dietary advice regarding IBS ideally have insight into how food affects their symptoms and are motivated to make changes.
  • In contrast, patients who are poor candidates for dietary therapy for IBS include persons who consume few culprit foods; persons at risk for malnutrition; persons at risk for food insecurity; and persons who have an eating disorder or uncontrolled psychiatric disorder.
  • RDNs who are affiliated with gastroenterology practices are the ideal persons to counsel patients with IBS about their diet and recommend treatment.
  • At the same time, the healthcare team should screen patients for disordered eating behaviors. Some research suggests that 20% of patients in gastroenterology practices have avoidant/restrictive food intake disorder, which places patients at risk for malnutrition.
  • Patients should prepare for a visit with an RDN by compiling a food and symptom diary for ≥ 3 days before the visit. They should also have an understanding of their previous diagnostic workup and interventions tried.
  • Soluble fiber is effective in the management of IBS. Soluble fiber is found in psyllium, ispaghula husk, corn fiber, calcium polycarbophil, methylcellulose, oat bran, and the flesh of fruits and vegetables.
  • Conversely, insoluble fiber may increase bloating and does not help other symptoms of IBS. Insoluble fiber is found in wheat bran, whole grains, and the skins of fruits and vegetables.
  • The low FODMAP diet is the most evidence-based dietary intervention for IBS. It improves symptoms and disease-related quality of life, particularly among patients with diarrhea-predominant IBS.
  • Short-term FODMAP diet taught by an RDN has minimal impact on micronutrient intake and may actually improve diet quality.
  • Dietary interventions should be effective within 6 weeks. If they are not effective in that time frame, the dietary intervention should be discontinued and other treatment instituted.
  • If the low FODMAP diet is successful in improving symptoms, then FODMAP foods should be gradually reintroduced over 6 to 10 weeks. This process will allow patients to identify particularly offensive foods and results in a less restrictive diet. Approximately three-quarters of patients can liberalize their diet using this approach.
  • Observational studies have found that most patients with IBS improve with a gluten-free diet, but clinical trials have suggested no effect. The routine application of a gluten-free diet to patients with IBS is not recommended.
  • Research is ongoing regarding the use of biomarkers, such as celiac-related genetic factors, to help predict patients’ response to dietary therapy for IBS, but the evidence for using such biomarkers is not strong enough to recommend their application in routine practice.

Clinical Implications

  • Fewer than half of patients with IBS respond to medical therapy, and the therapeutic gain of active treatment over placebo is limited to 7% to 15%. More than 80% of patients with IBS state that their symptoms are related to meals. Carbohydrates are the macronutrient most often implicated in promoting IBS symptoms, and the group of carbohydrates known as "FODMAPS" are particularly implicated in making IBS more severe.
  • The FODMAP diet has the most evidence of effectiveness of all dietary interventions for IBS. Dietary counseling for IBS is best given by an RDN, and diets that do not improve symptoms within 6 weeks should be discontinued. A successful trial of a FODMAP diet should be followed by the gradual reintroduction of foods to find particular triggers.
  • Implications for the healthcare team: Collaboration with a registered dietitian nutritionist (RDN) is key member of the healthcare team for optimal dietary management of IBS.


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