Maitreyi Raman, MD, MSc, on the Low FODMAP Diet in Patients With IBS

While it has been established that certain foods can worsen the symptoms of irritable bowel syndrome (IBS), the effects of specific dietary therapies are less well understood.

At present, a diet low in fermentable, oligosaccharides, disaccharides, monosaccharides, and polyol (FODMAP) is supported by the literature as a potentially effective treatment for the symptoms of IBS. 

To learn more about the effects of a low FODMAP diet on IBS symptoms, Gastroenterology Consultant spoke with with Maitreyi Raman, MD, MSc, a clinical associate professor of medicine in the Calgary Division of Gastroenterology and Hepatology at Foothills Medical Centre in Alberta, Canada.

GASTRO CON: What is currently known about the effects of a low FODMAP diet on IBS symptoms?

MR: The universal theory regarding why restricting these fermentable carbohydrates seems to have effect in the gut is that these carbohydrates are not absorbed well, or at all, in the small intestine. Because of this, they have an osmotic load, and within the small intestine, they draw a large amount of fluid into the gut. Having that extra fluid can cause symptoms of cramping and bloating, even prior to any liberation of gas or any other metabolic effects. Once the stool or the undigested food and fluids pass through the intestine and into the colon, a lot of natural bacteria in the colon can ferment the undigested foods and liberate multiple types of gases.

The combination of the fermentation process that results in gas production, together with a high fluid load in the intestine, leads to the symptoms observed in IBS. Restricting those malabsorbed carbohydrates reduces the fluid and fermentation leading to reduced gas production, resulting in less abdominal pain, bloating and diarrhea. This has now been validated in 4 randomized control studies,1 and fairly accepted in the medical community and by patients as perhaps the first-line of therapy in the management of IBS.

GASTRO CON: What concerns, if any, are there with following a low FODMAP diet?

MR: The first big concern is whether it really has a true effect on symptoms. The studies that have been published do not have the most ideal control group. For example, the studies were randomized, and all patients who received treatment with the low FODMAP diet did receive it as instructed. The patients who did not receive treatment with the low FODMAP diet had various other control diets. In 2 studies, patients did not have any specific diet. In the 2 other diets that did have proper control groups, those two studies did not show the same level of benefit as the low FODMAP diet did against no structured dietary therapy. Because of the study designs that still are not ideal, there is a little bit of reluctance overall for the medical community to say, “Yes, this is it. This is the magic therapy for IBS.”—Just because the data here still require more development and more nuance.

The second possible limitation of the low FODMAP diet, which is probably the bigger concern, is that by restricting these fermentable carbohydrates, many of these carbohydrates are healthy foods. They are usually certain types of fruits and vegetables that we would typically consider to have anti‑inflammatory or beneficial properties. By restricting these types of food, the concern is that our patients are putting themselves at risk for further nutrient deficiencies. How do these restrictions over time change that gut microbiome? This is another area of interest in the medical community and with patients in general.

The gut microbiome has been referred to as the forgotten organ or the lost organ. The impact of the gut microbiota and health has really had a resurgence and interest, concomitantly, in the last decade or so. Continued use of the low FODMAP diet can lead to changes in the microbiome as well as possible nutrient deficiencies. This diet is a factor. We typically recommend that patients should not implement this on their own. It needs to be done under the supervision of a dietitian. If there is a dietitian involved, and patients receive follow‑up, then usually these nutrient-deficiency concerns can really be minimized.

GASTRO CON: What factors need to be considered before prescribing the low FODMAP diet to a patient with IBS?

MR:  Firstly, clinicians need to establish that the patient does have IBS because there are many other things that can mimic IBS. Once all other conditions are ruled out, ask your patient about whether he or she has identified any relationships between food/diet and onset or worsening of their symptoms. If it is a resounding “yes,” then I would recommend the low FODMAP diet as first-line therapy. In that setting, the diet should be implemented and discussed via a consultation with a dietitian. The initial rigorous phase of the diet should only be implemented for 4 and 6 weeks. It was never intended to be a long‑term diet because of the potential of risks for nutrient deficiencies. Once the patient starts to have improvement in his or her symptoms, then he or she can start reintroducing foods into the diet, under the guidance of the dietitian.

Sometimes food does not affect patients’ IBS symptoms; sometimes stress or mood is a bigger trigger. For these patients, the role of the low FODMAP diet is less clear. If the patient seems to identify more psychological types of triggers, I may start therapy with a fiber supplement and probiotics, because they have few adverse effects and are reasonably effective. Patients with psychological comorbidities may have less of a response to this approach, though. In that case, I would typically recommend those patients to cognitive behavioral therapy or tricyclic antidepressants.



  1. Schumann D, Klose P, Lauche R, Dobos G, Langhorst J, Cramer H. Low fermentable, oligo-, di-, mono-saccharides and polyol diet in the treatment of irritable bowel syndrome: a systematic review and meta-analysis. Nutrition. 2018;45:24-31.