Irritable bowel syndrome is a complex digestive condition that interferes with the daily lives of millions of people worldwide. Typically occurring in episodes, the condition is characterized by symptoms such as moderate to intense abdominal pain, bloating and gas. This set of digestive symptoms is not unique to IBS; therefore, to accurately diagnose the condition, health care professionals must rule out other issues such as celiac disease, small intestinal bacterial overgrowth and food allergies.
While diet does not cause IBS, individualized nutrition therapy can significantly lessen symptoms through identification and restriction of trigger foods. Fermentable oligosaccharides, disaccharides, monosaccharides and polyols, or FODMAPs, have been identified as a group of short-chain carbohydrates that are rapidly digested and poorly absorbed in the gut, thus provoking excess fluid and gas in the bowels of many people with IBS. FODMAPs are naturally occurring carbohydrates found in foods such as apples, watermelon, asparagus, broccoli, milk and beans and are sometimes added to food as sweeteners.
Although some carbohydrates under the FODMAP umbrella, such as lactose and fructose, have been targeted in IBS therapy in the past, research on diet therapy addressing all FODMAPs as a group only began within the last decade. Research started in Australia in 2006, and subsequent studies have occurred elsewhere, including the United Kingdom, New Zealand, Scandinavia and the U.S. The results have been clear: When people with IBS consumed high amounts of FODMAPs, their symptoms got worse; when they restricted FODMAPS, their symptoms improved.
Now with enough evidence to support its use, a low-FODMAP diet is recommended as a nutrition prescription for patients with IBS in the Academy of Nutrition and Dietitics’ Nutrition Care Manual. Client education materials for a low-FODMAP diet will be available in the NCM later this year.
Nonetheless, doctors caution that low-FODMAP diet therapy is not a cure for patients with IBS. Individual response to the diet varies, and some people with IBS experience little relief from following a low-FODMAP diet. And while a low-FODMAP diet produces significant results in most IBS patients, it doesn’t always eliminate all symptoms. For instance, some patients may experience relief from gas and bloating, but their irregular bowel patterns remain.
FODMAP expert Patsy Catsos, MS, RDN, LD, began using low-FODMAP diet therapy in her private practice almost a decade ago. To date, she has helped thousands of patients through the diet and says that “the FODMAP elimination diet is more than just a list of foods — it’s a process. To get the best outcomes, patients need a strategic plan, and that’s where the dietitian comes in.”
One concern about following a low-FODMAP diet is the effect it may have on a patient’s gut microbiota. Evidence shows IBS patients have different gut microbiomes compared to the healthy population. Preliminary research suggests taking a probiotic supplement during low-FODMAP diet therapy can prevent the washout of beneficial gut bacteria, leading some FODMAP experts to recommend this type of supplement to people with IBS on the diet.
In addition to IBS, limited evidence shows promise of a low-FODMAP diet for people with inflammatory bowel disease, which is a separate medical condition (an autoimmune disease characterized by chronic inflammation; includes Crohn’s disease and ulcerative colitis). Some researchers suspect a low-FODMAP diet may help alleviate digestive symptoms in people with non-celiac wheat sensitivity, but the diet has not been validated in this population.
Not all FODMAP-containing foods worsen IBS symptoms for all patients, which is why the diet therapy is conducted in two phases. To identify specific foods that trigger symptoms in a patient, phase 1 restricts all high-FODMAP foods and phase 2 gradually reintroduces them.
Phase 1 typically lasts up to eight weeks and is when patients feel most challenged by the restrictiveness of the diet. Elimination and reintroduction of FODMAP-containing foods is the only effective strategy to identify trigger foods in patients with IBS. Reliable assessment methods such as hydrogen breath tests are available to detect some, but not all, FODMAP malabsorption, but these tests are capable of false positives and are not perfect. Because long-term evidence is not available and there is a risk of nutritional inadequacy if the diet is poorly planned, restricting high-FODMAP foods should be temporary and reintroduction should be as quick as possible in accordance with the patient’s symptoms.
Patients and physicians should work with an RDN who is trained in administering a low-FODMAP diet to ensure the success of the nutritional therapy. According to low-FODMAP diet educator Kate Scarlata, RDN, LDN, “The low-FODMAP diet has many nuances, and online resources are often outdated, making the IBS patient confused and frustrated. The role of the dietitian is to be well-prepared with the latest and most accurate low-FODMAP diet research to successfully guide the patient with this effective nutrition intervention.” While research shows good patient compliance of about 75 percent following the diet, it is restrictive by nature.
Barriers include expense of low-FODMAP specialty foods, dislike for the taste, unwillingness to follow the diet and the challenge of identifying and selecting low-FODMAP foods when eating away from home. Additional challenges are the lack of defined cutoff values for high- and low-FODMAP foods and shortage of FODMAP content on food packaging.
Two voluntary certifications for low-FODMAP food products are available, one from Monash University and the other from FODMAP Friendly, both of which have access to FODMAP laboratories to conduct food testing. These seals are on few products in grocery stores today, but likely will increase as the diet gains popularity. Dietitians interested in learning more about FODMAP diet therapy are encouraged to read books by reputable FODMAP experts, seek continuing education opportunities such as workshops and trainings led by FODMAP experts and use the Monash University low-FODMAP diet app.