12 January - 20 June 2016

Can a low FODMAP diet reduce symptoms of IBS?

Clinical and Experimental Gastroenterology has published a review which summaries studies which investigate the management of irritable bowel syndrome (IBS) using restriction of Fermentable Oligosaccharide, Disaccharide, Monosaccharide, and Polyols in the diet (low FODMAP).

Clinical and Experimental Gastroenterology has published a review which summaries studies which investigate the management of irritable bowel syndrome (IBS) using restriction of Fermentable Oligosaccharide, Disaccharide, Monosaccharide, and Polyols in the diet (low FODMAP).

IBS is a chronic gastrointestinal disorder with symptoms including abdominal pain, diarrhoea, bloating and constipation.  Pharmacological treatments may provide some relief, however diet manipulation, amongst other techniques, could provide further benefits. 

Two thirds of IBS patients perceive their symptoms to be food-related.  Foods that are thought to trigger symptoms include incompletely absorbed carbohydrates, fatty foods, coffee, alcohol and spicy foods.  Early studies focused on elimination diets followed by re introducing food with symptoms improving for 15-50% of study participants.  Other studies investigated using a low lactose diet, probiotics, fibre supplementation and gluten free diets.  All have shown mixed results.  It has been suggested that fructans and galacto-oligosaccharides, the carbohydrate component of wheat rather than gluten may be responsible for the IBS symptoms experienced by patients with noceliac gluten sensitivity (NCGS) and IBS.

FODMAPs are short-chain poorly absorbed carbohydrates.  They include fructose, lactose, fructans, galacto-oligosaccharides, and polyols or sugar alcohols.  However not all FODMAPs are reported to make abdominal symptoms worse in IBS patients.  It has been found that poor absorbency of FODMAPs can lead to net secretion of fluid into the small intestine leading to abdominal symptoms.  One study found that high consumption of FODMAPs led to increased intestinal output of 22%.  Another study found that abnormal accumulation of fluid in the small intestine led to diarrhoea. The review notes that colonic microbiota can rapidly ferment FODMAPs leading to colonic distention from gas production.  A low FODMAP diet has been found to reduce fermentation and these related symptoms. 

Results from studies on a low FODMAP diet and IBS have been consistent in showing improved overall symptoms in adult patients.  Although Gearry et al. report many of the studies are retrospective, or prospective or uncontrolled and are subjected to being biased and confounding factors.  The team found two controlled trials and six randomised controlled trials which evaluated low FODMAP diet and IBS.  The majority involved only a small number of participants with outcome being measured by GI symptoms.  The list of food allowed was not provided in all studies and a couple included foods which are not part of the low FODMAP diet.  The reviews mentions a recent study which investigates a low FODMAP diet with an Australian diet and took into account confounding factors.  The authors of this study found that after 7 days on the low FODMAP diet, 70% of participants reporting feeling better.  Another study cited in this current review supported FODMAP, as food triggers were also investigated. 

Gearry et al. note limitations of the low FODMAP diet including “lack of clear cutoff levels for FODMAP content in foods and nonavailablity of information on FODMAP content on food packaging.”  The low FODMAP diet does not help all GI symptoms for all IBS patients and the health implications of long-term low FODMAP are unknown.  The FODMAPs Inulin fructans and galacto-oligosaccharides are prebiotics, which are associated with the growth of “beneficial bacteria.” Studies have found that avoidance of FODMAP foods may reduce total bacterial abundance which could result in potential adverse health effects. 

Gearry et al conclude their review by stating that “evidence to date indicates that restriction of FODMAPs is an effective dietary intervention for reducing IBS symptoms.” However they note that long term assessment of low FODMAP diets are required to “ascertain any adverse outcomes from effects on the gut microbiota.” 

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