Irritable Bowel Syndrome (IBS) is fairly common medical diagnosis that a registered dietitian will encounter. Twenty percent of the North American population suffers from IBS and as many as two-thirds of patients report specific food triggers which subsequently leads to food restriction. Though diet does not cause IBS, it can be optimized to improve symptoms and patient quality of life.
One of the strategies to combat IBS symptoms is a diet low in particular classes of carbohydrates: fermentable oligosaccharides, disaccharides, monosaccharides and polyols (sugar alcohols) (FODMAPs). In patients with IBS, these carbohydrates are poorly absorbed and are rapidly fermented by GI bacteria. The fermentation process leads to increased water and gas in the small intestine—which results in the uncomfortable symptoms of IBS. A low FODMAP diet is characterized by a reduction in wheat, elimination of lactose and low in disproportionate fructose. The diet appears to effectively control symptoms in ~50-70% of patients with IBS.
FODMAP containing foods are everywhere in an American diet. Wheat, artichokes, chicory root (the fiber added to many foods with “added fiber”) and garlic contain FODMAPs. Even healthy foods can be less-than-ideal for IBS patients; honey, apples, pears, watermelon, mushrooms, onions and cauliflower can be extremely irritating to the stomachs of IBS patients. Though the mechanisms of altered absorption are different per subtype of carbohydrate, the effects from each type are cumulative in the gut. For example, a high fiber cereal for breakfast, a salad with onions for lunch and pasta for dinner all contribute FODMAPs; the cumulative effect over a patient-specific threshold can result in symptoms.
What is even more interesting with FODMAPs is their symptoms are subclass-specific. A patient experiences gas or diarrhea, it is likely from fructan consumption, which affects the sigmoid colon. Conversely, fructose is an irritant to the small intestine which can lead to constipation or pain. An RD can piece together a patients diet with their GI symptoms and tailor a diet very specific to their needs. Thus, the RD plays an essential role in the management of IBS symptoms. With each patient, practitioners need to conduct detailed dietary recalls and identify the foods that contain FODMAPs and work with the patient to optimize their nutrition plan.
Nee J, Scarlata K. Using Science to Further Define FODMAPs and Simplify Patient Education. Food and Nutrition Conference and Expo 2016. Date: October 17, 2016