Low FODMAP Diet in Irritable Bowel Syndrome: Controversies and Practicality

Irritable bowel syndrome (IBS) is one of the most common diagnoses made and encountered by gastroenterologists. Up to 50% of all referrals to gastroenterologists can be for IBS¹. Within the world, IBS is relatively prevalent, with rates as high as 45%, depending on the country.² IBS is defined according to the Rome IV criteria, which state that a patient must have recurrent abdominal pain on average at least 1 day per week in the last 3 months, associated with 2 or more of the following: pain associated with a change in stool frequency, stool form, or appearance, and pain related to defecation.³ IBS is typically a diagnosis of exclusion, and other gastrointestinal conditions should be ruled out before making the IBS diagnosis, such as inflammatory bowel disease, celiac disease, small intestinal bacterial overgrowth, and potentially even malignancy.

The exact pathophysiology leading to IBS is yet to be fully elucidated. However, it is believed that a patient’s dietary intake and exposure can play a significant role. Certain foods may be responsible for altering a patient’s microbiome, predisposing them to intestinal inflammation as well as contributing to visceral hypersensitivity, all of which can lead to developing IBS symptoms. One such food group that has significant research to support its importance within IBS are the fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs).

Foods high in FODMAPs are poorly absorbed, leading to increased fermentation when in contact with gut bacteria, which can lead to bloating. In clinical trials, a low FODMAP diet has shown significant benefit, with efficacy rates between 50% and 87%.⁴ With the growing data on the low FODMAP diet, there have been several challenges and controversies that have come to light that significantly affect patient care and outcomes. It is important to note that trials evaluating these types of diets, especially low FODMAP diets, can be challenging to design and run based on the challenges associated with a “placebo” diet group. Recently, Halmos et al published an informative review of some of the controversies encountered with the low FODMAP diet.⁴

On a practical note, the low FODMAP diet is relatively selective and challenging to follow for a prolonged amount of time. The exact time frame that patients with IBS should follow and maintain this diet is unclear, with a prolonged course potentially leading to some nutritional deficiencies. To avoid overrestricting a patient’s diet, some physicians will advocate for a more restrictive FODMAP diet initially, followed by occasional re-introduction of certain foods (such as lactose or fructose) to see whether those specific items will affect the patient’s IBS symptoms. This could potentially lead to a less restrictive, individualized diet, but it could be practically challenging for a patient to follow and could take a significant amount of time to complete. Also, some patients are reluctant to re-introduce certain foods that may cause re-emergence of symptoms, especially if they have had a significant response to the low FODMAP diet.

Physicians frequently recommend a low FODMAP diet, but may not have all the in-depth knowledge that a dietician can have with regard to all the available food products. Most physicians can provide educational handouts, but only 20% of physicians actually refer patients to a dietitian.⁵ Even when a referral is made, not all patients may have access to a dietician or have medical coverage that covers dieticians, with out-of-pocket costs potentially prohibitive. The ideal low FODMAP protocol has yet to be developed, with some dieticians recommending more restrictive diets up front compared with those who may recommend more liberal low FODMAP diets. These types of protocols can be difficult to enact when certain patients may already have restrictive diets, such as those with diabetes, cardiovascular disease, or certain food allergies/intolerances. A “FODMAP gentle” diet may be a more reasonable, less restrictive approach that some patients could respond to.⁶ This type of diet would aim to limit certain high FODMAP foods such as wheats/rye, milk and yogurt, legumes, and certain fruits (apple, pears) and vegetables (onion, mushrooms).^4,6

Patients may not respond to a low FODMAP diet for a multitude of reasons, including dietary indiscretions, low adherence, and having an underlying diagnosis other than IBS. Even with patients with true IBS, a low FODMAP diet may not work if their underlying pathophysiology causing the IBS is not mediated by foods high in FODMAPs. Further studies are needed in the future to help better predict which patients with IBS may be responders to a low FODMAP diet. These types of studies will need to look at different subtypes of IBS (IBS-diarrhea, IBS-constipation, IBS-mixed) and improved breath testing, as well as evaluating underlying gut microbiome profiles and how they may affect a response to a low FODMAP diet.

References

1. Everhart JE, Renault PF. Irritable bowel syndrome in office-based practice in the United States. Gastroenterology. 1991;100(4):998-1005.

2. Lovell RM, Ford AC. Global prevalence of and risk factors for irritable bowel syndrome; a meta-analysis. Clin Gastroenterol Hepatol. 2012 Jul;10(7):712-721.

3. Mearin F, Lacy BE, Chang L, et al. Bowel disorders [published online February 18, 2016]. Gastroenterology. doi:10.1053/j.gastro.2016.02.031

4. Halmos EP, Gibson PR. Controversies and reality of the FODMAP diet for patients with irritable bowel syndrome.  J Gastroenterol Hepatol. 2019 Jul;34(7):1134-1142.

5. Lenhart A, Ferch C, Shaw M, Chey WD. Use of dietary management in irritable bowel syndrome: results of a survey of over 1500 Unites States gastroenterologists. J. Neurogastroenterol. Motil. 2018;24:437-51.

6. Halmos EP. When the low FODMAP diet does not work.  J Gastroenterol. Hepatol. 2017;32:69-72.