The Health Implications of FODMAP

According to the most recent data from the National Institute of Diabetes and Digestive and Kidney Diseases, more than 70 million people are affected by all digestive disorders. The dominant disorders include chronic constipation, gallstones, and a myriad of gastrointestinal (GI) infections, including those derived from foodborne illness. Functional gastro-intestinal disorders include three major categories, namely esophageal, gastroduodenal, and bowel disorders (Manning and Biesiekierski 2018).

One dietary approach in managing these disorders is called FODMAP (Marcason 2012). FODMAP is an acronym for Fermentable Oligo-, Di and Mono-saccharides, and Polyols. This dietary approach was initially reported approximately 15 years ago, when a group out of Australia noted that elimination of specific foods could reduce complaints from patients presenting gastrointestinal symptoms, particularly those associated with Crohn’s disease (Gibson and Shepherd 2005), then later applied to those diagnosed with irritable bowel syndrome (IBS) and fructose malabsorption (Shepherd and Gibson 2006).

Many of the foods that are traditionally associated with health promotion are reduced or eliminated in FODMAP regimens. For example, the typical FODMAP food pattern reduces or eliminates fructo-oligosaccharides (wheat, rye, onions, garlic, artichokes), galacto-oligosaccharides (legumes), lactose (dairy products), fructose (most fruits and honey), sorbitol (many fruits and some sugar-free products), and mannitol (mushrooms, cauliflower, and some sugar-free products).

Some suggest that these foods induce or contribute to GI symptoms by increasing microbial fermentation and osmotic activity (Muir et al. 2007). Others suggest dietary oligosaccharides may reduce total microbial abundance in the GI tract, thus altering the microenvironment profile, modifying GI wall expansion status, luminal water content, and gut motility, as well as the fluctuating microbial fermentation profile of short-chain fatty acids (Eswaran, Farida, Green, Miller, and Chey 2017). At this point, the current clinical experiences with FODMAP interventions indicate variable outcomes among patients.

Studies on low-FODMAP dietary patterns may impact regulation of the immune system and an array of cytokines. A small and short-term study among subjects presenting diarrhea-predominant or mixed IBS demonstrated reduced symptoms. These observations were supported by reduced levels of two pro-inflammatory cytokines, butyric acid, and total short-chain fatty acids (Hustoft, et al. 2017). A similar study among 40 patients indicated a low-FODMAP dietary pattern over a 3-week period could reduce histamine and alter the gut microbiota as evidenced by lower gas production (McIntosh, et al. 2017). These results are consistent with an earlier study among 30 IBS patients in Australia. Following a study with crossover design, the low-FODMAP intervention reduced functional gastrointestinal symptoms (Halmos, Power, Shepherd, Gibson, and Muir 2014). An additional study among 30 hospitalized patients fed enterally yielded similar results following a 14-day low-FODMAP intervention (Yoon, et al. 2015). The nutritional status of these individuals was also improved as suggested by increased serum transferrin levels in the moderate-FODMAP group.

 A FODMAP dietary pattern now represents a standard intervention among patients presenting functional gastrointestinal disorders, particularly IBS. The long-term effects of a FODMAP dietary pattern or routine administration may improve some aspects of immune signaling and alterations in microbiota yet may also pose a number of limitations. Those limitations include variations in patient responses; differences in oligosaccharide chain length, which influences fermentability; disparities in lactose tolerances; differences in absorptive capacity when challenged with monosaccharides, such as free fructose that is innate to fruit; and distinctions of polyols that are found in fruits (apples, pears, stone fruits, cauliflower, mushrooms, snow peas) and some non-nutritive sweeteners.

These and other variations in patient responses, such as a need to consider individual tolerances based on yet undefined criteria other than patient subjective reports, broadly include nutrient balances (as specific wholesome foods are eliminated), individual dietary restrictions due to other maladies, and differences in food preparation skills (Barrett 2017). On the other hand, one needs to consider potential stages during which some foods are reintroduced or when diet is expanded and, of course, there is always patient compliance, the success or failure of which depends on potential absence or return of symptoms of functional bowel disorders (Tuck and Barrett 2017).

The low-FODMAP diet and the associated regimens for reintroduction of the putatively offending foods has certainly shown symptomatic benefits in some patients with IBS. Reduction of osmotic load and gas production in the distal small bowel and proximal colon does appear to provide significant short-term benefit. Genuinely effective dietary interventions for vexing disorders are always exciting, but it remains to be seen whether long-term risks to nutritional status, gut microbiome, and enterocyte metabolism may dampen the mounting enthusiasm for this intriguing approach in clinical practice.

Roger Clemens, DrPH, CFS, Contributing Editor
Adjunct Professor, Univ. of Southern California’s School of Pharmacy, Los Angeles, Calif.
[email protected]