Looking Beyond Gluten
Over the past decade, gluten avoidance has become the most popular dietary trend in the United States, with over 100 million Americans consuming gluten-free products, most of whom do not have celiac disease.
In fact, the term non-celiac gluten sensitivity (NCGS) was minted to describe individuals who manifest a clinical disorder related to ingestion of gluten. NCGS is characterized by a series of self-reported gastrointestinal (GI) symptoms similar to those with irritable bowel syndrome (IBS): abdominal pain, gas and bloating, nausea, diarrhea, or constipation.[2,3,4,5,6] While data seemed to convincingly support a role for gluten in causing many of these GI symptoms, recent studies have suggested that there is more to the story.[7,8] It may be incorrect to attribute any clinical response to the presence or absence of gluten, as differences in the content of other dietary components (eg, wheat proteins, poorly absorbed carbohydrates) may also be responsible. This was clearly shown by Biesiekierski and colleagues in a double-blind crossover study of persons with self-reported NCGS who were feeling well on a gluten-free diet. These patients improved further on a diet in which FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) were eliminated. GI symptoms consistently and significantly improved for all participants during the phase of reduced intake of FODMAPs. When these patients were re-challenged by reintroduction of gluten into the otherwise low-FODMAP diet, they did not experience a specific or dose-dependent relapse.
Possible Explanations for FODMAP Sensitivity
It has long been recognized that patients with IBS may experience sudden or worsening abdominal pain and bloating after ingesting certain foods, including historically recognized "culprits" like milk and other dairy products, legumes, and select fruits. The hypothesized mechanisms have included immune and mast cell activation, mechanoreceptor stimulation, and chemosensory activation.[10,11] The most recently cited triggers are short-chain carbohydrates collectively known as FODMAPs. A low-FODMAP diet has been reported to induce a clinical response in 50%-80% of patients with IBS, with specific improvement in bloating, flatulence, diarrhea, and global symptoms.[12,13,14]
Components of FODMAPs are nearly ubiquitous and include fructose (found in stone fruits and sweeteners), lactose (dairy products), fructans (wheat-based products), galacto-oligosaccharides (legumes), and polyols such as xylitol and mannitol (fruits and artificial sweeteners). These highly fermentable carbohydrates are poorly absorbed from the small intestine and thus enter the colon, where they osmotically increase luminal water volume, induce gas and short-chain fatty acid production through fermentation by colonic bacteria, and increase intestinal motility. This leads to luminal distension, bloating, and diarrhea. FODMAPs may also affect the gut microbiota, gut immune function, and the gut mucosal barrier—factors that might also be involved in generating GI symptoms in patients with visceral hypersensitivity.[12,13]
Gibson and coworkers thus proposed that reduction in the dietary intake of these indigestible or slowly absorbed, short-chain carbohydrates would minimize bloating and stretching of the intestinal wall, thereby decreasing bowel contractions and pain. This broad reduction approach differed from previous dietary strategies in which one or two specific species of carbohydrates (eg, lactose, fructose, or sorbitol) were restricted.
The early success has allowed the FODMAP diet to become a popular option, and resources that describe the FODMAPs composition of various foods are readily available.[10,17] These known "gas-producing foods" are being avoided by patients plagued by excessive flatulence and bloating. This may indeed be a viable management option, but restriction may have important unintended consequences, as FODMAPs variably exert important physiologic effects: increasing stool bulk, enhancing calcium absorption, modulating immune function, decreasing serum cholesterol levels, and stimulating the growth of certain microbial groups such as Bifidobacteria (a prebiotic effect). In addition, bacterial fermentation of FODMAPs results in the production of short-chain fatty acids that exert a trophic effect on colonocyte metabolism.
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Cite this: Gluten Sensitivity Aftershock! Is a Low-FODMAP Diet the Next Big Thing? - Medscape - Sep 20, 2017.