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Managing IBS with a Low FODMAP Diet

Mechanisms and efficacy explored

by Ashley Jordan Ferira, PhD, RDN

Most people have heard of, or know somebody who suffers from irritable bowel syndrome (IBS). IBS is not a single condition but rather a group of symptoms associated with the gastrointestinal (GI) tract that includes abdominal pain and changes in bowel movements such as constipation or diarrhea.1 IBS affects 10-15% of US adults, with women being twice as likely as men to develop IBS.1 Costs associated with treating IBS symptoms are estimated to  be $1.7 billion and $10 billion in the US alone.2 Currently, pharmaceuticals are the main treatment option for IBS sufferers, but many medications only target single symptoms.3 While no single cause nor cure exists for IBS, researchers and clinicians continue working to identify treatments that may mitigate multiple symptoms.

A key research focus area is the interaction between IBS and diet. Patients often report that functional GI symptoms experienced with IBS worsen when certain ‘trigger foods’ are consumed. One particular intervention for IBS involving the dietary restriction of short-chain fermentable carbohydrates and sugar alcohols is known as the low FODMAP (fermentable oligosaccharide, disaccharide, monosaccharide and polyol) diet. FODMAPs are common in many foods at varying levels, but not all carbohydrates contain FODMAPs. Although the food list to avoid is lengthy, some foods that are particularly high in FODMAPs include wheat, garlic, onion, beans, lentils, legumes, diary, sweeteners, and many fruits and vegetables.4 A low FODMAP diet usually involves two phases: the elimination of FODMAP-containing foods over the course of 4 – 6 weeks, followed by a gradual reintroduction.4

In the publication Gut, researchers Staudacher and Whelan reviewed the current body of research on low FODMAP diets.5 Their review discussed gut-related mechanisms mediating the effects of a low FODMAP diet on IBS symptomology. They indicated that studies using magnetic resonance imaging (MRI) technology have clearly shown that digestion of short-chain fermentable carbohydrates increases water volume in the small intestine (referred to as an osmotic effect) and gas production in the colon, which can result in GI pain and diarrhea in IBS patients.5

As the authors note, there are over 10 studies on the efficacy of the low FODMAP diet’s ability to minimize IBS symptoms. Limitations of earlier studies (e.g. retrospective-design and lacking comparator groups) have been addressed by randomized controlled clinical trials, which have demonstrated improvements in IBS symptoms such as bloating, flatulence and diarrhea in 50 to 80 percent of patients studied.5

The authors concluded that strong, consistent evidence supports low FODMAP diets for IBS symptom relief and management.5 Like any restrictive eating pattern, the low FODMAP approach has its limitations, including creating nutrient gaps (particularly fiber, calcium, iron, zinc, vitamin D, B vitamins, and natural antioxidants)4 due to the avoidance of nutrient-dense fruits and vegetables and is not recommended as a long-term dietary strategy. Additionally, research data indicates that decreasing FODMAPs results in microbiota changes, particularly reducing Bifidobacterium species,7 which has been associated with a worse IBS symptom profile.5,7

Additional interventions to address nutrient gaps and microbiota alterations, such as nutrient supplementation and evidence-based probiotic strain(s),7-8 may be necessary. Finally, the authors point out that highly restrictive diets are difficult to maintain and may not be suited for all patients. Future FODMAP research study designs should address existing research gaps by including dietary adherence information, larger numbers of patients, and long-term diet adherence duration.9

Why is this Clinically Relevant?

  • IBS symptomology is multifactorial, and effective treatments that address multiple symptoms are needed
  • Clinical trial evidence indicates that the low FODMAP diet can help improve IBS symptoms in a large proportion of patients3
  • Low FODMAP diets often restrict fiber and key micronutrients; nutritional gaps should be remedied through other means, such as supplementation
  • Multi-strain probiotic supplementation may be used to address the microbiota dysbiosis induced by the low FODMAP dietary pattern5
  • Low FODMAP diets are restrictive and may not be an ideal fit for all IBS patients

Link to abstract


  1. Grundmann O, Yoon SL. Irritable bowel syndrome: epidemiology, diagnosis and treatment: an update for health-care practitioners. J Gastroenterol Hepatol. 2010;25(4):691-699.
  2. Hulisz D. The burden of illness of irritable bowel syndrome: current challenges and hope for the future. J Manag Care Pharm. 2004;10(4):299-309.
  3. National Institute of Diabetes and Digestive and Kidney Diseases. Treatment for Irritable Bowel Syndrome. October 19, 2017.
  4. Stanford Health Care. Low FODMAP Diet. Accessed October 18, 2017.
  5. Staudacher HM, Whelan K. The low FODMAP diet: recent advances in understanding its mechanisms and efficacy in IBS. Gut. 2017;66(8):1517-1527.
  6. Catassi G, Lionetti E. The low FODMAP diet: many question marks for a catchy acronym. Nutrients. 2017;16(9): pii: E292.
  7. Staudacher HM, Whelan K. Altered gastrointestinal microbiota in irritable bowel syndrome and its modification by diet: probiotics, prebiotics and the low FODMAP diet. Proc Nutr Soc. 2016;75(3):306-318.
  8. Staudacher HM, Lomer MCE, Farquharson FM, et al. A diet low in FODMAPs reduces symptoms in patients with irritable bowel syndrome and a probiotic restores Bifidobacterium species: a randomized controlled trial. Gastroenterology.2017;153(4):936-947.
  9. Marsh A, Eslick EM. Does a diet low in FODMAPs reduce symptoms associated with functional gastrointestinal disorders? A comprehensive systematic review and meta-analysis. Eur J Nutr. 2016;55(3):897-906.

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