Short-chain carbohydrates found in our diet which are not digested in the small intestine and are rapidly fermented by colonic bacteria are commonly referred to as FODMAPs (fermentable oligo-,di-, monosaccharides and polyols). Although numerous benefits have been associated with FODMAP consumption, the ingestion of these carbohydrates by individuals suffering from functional gastrointestinal disorders such as Irritable Bowel Syndrome (IBS) is often associated with gastrointestinal discomfort and symptoms, including altered bowel habits, bloating and excessive abdominal pain and cramping. The effect of FODMAPs on IBS symptoms appears to be in part driven by luminal distention due to fermentation products such as hydrogen and methane generated by the action of gut microbiota on the ingested FODMAPs and the inherently osmotically active nature of the FODMAPs.
The dietary restriction of these short fermentable carbohydrates (low FODMAP diet) is thus considered an important intervention in the dietary management of IBS. The low FODMAP diet involves the restriction of multiple fermentable oligosaccharides (fructans, galacto-oligosaccharides/GOS), disaccharides (lactose), monosaccharides (fructose when in excess of glucose) and polyols (eg, sorbitol, mannitol). This list of FODMAPs is often quoted and extensively investigated. They are also the FODMAPs that are exclusively tested when certifying food ingredients, products, and recipes as low FODMAP. However, as some recent studies show, a different group of soluble, non-digestible fermentable carbohydrates also demands attention in this regard.
Whole grains and pulses are rich in a number of phytonutrients and bioactives and have several reported health-promoting effects. Not surprisingly, nearly every cuisine has its own variation of whole grains and pulses as they naturally complement each other to provide a wholesome culinary and nutritional experience. However, two main classes of FODMAPs are found in these popular dietary components - fructans in gluten-containing whole grain cereals such as wheat, spelt, barley, and rye and α-galacto-oligosaccharides (GOS) in pulses such as peas, lentils, and chickpeas. Hence these ingredients are often avoided by individuals on a low FODMAP diet. Gluten-free dietary ingredients (e.g., rice, millet, buckwheat) do not accumulate large amounts of any of the FODMAPs commonly investigated making them a popular choice as alternative whole grains for people following the low FODMAP diet. However, some recent studies by researchers at University College Cork, Ireland, have once again highlighted earlier findings that buckwheat can accumulate significant amounts of a particular class of soluble indigestible carbohydrates that may act as FODMAPs - fagopyritols.
Fagopyritols are galactosyl derivatives of D-chiro-inositol that accumulate in seeds of common buckwheat. Based on the number of galactose residues attached to chiro-inositol, they are primarily classified into mono-,di- and tri- galatosyl derivatives of D-chiro-inositol. Accumulation of these carbohydrates appears to confer desiccation tolerance to buckwheat seeds similar to the function of GOS in GOS-accumulating cereals and pulses. Fagopyritols form 40% of total soluble carbohydrates in hulled kernels of at least two cultivars of common buckwheat. Bran milling fractions of common buckwheat contain 6.4 g of total soluble carbohydrates per 100 g of dry weight, of which 40% are fagopyritols. Fagopyritols as a carbohydrate class are not restricted to buckwheat and have also been shown to accumulate in seeds of soybean, lentil and chickpeas.
Fagopyritols appear to have a mix of structural properties of the two key molecular components they are comprised of - galactose residues and D-chiro-inositol. Similar to GOS they require the enzyme α-galactosidase for their hydrolysis and absorption into the intestinal mucosa. It is well known that the human gut lacks this enzyme. Fagopyritols are, thus, non-digestible carbohydrates and could lend themselves to fermentation by the colonic microbiota. Although there are studies indicating a beneficial, blood glucose lowering effect from fagopyritols for diabetes patients, given their structural and functional similarity to GOS, these carbohydrates are suspected to have a similar impact on the sensitive gut, such as that of IBS patients, possibly inducing symptoms such as flatulence. In addition to fagopyritols, buckwheat contains so called cyclitols and their α-galactosides. These are precursor and intermediate compounds in the biosynthesis of fagopyritols. Although in vitro and in vivo studies are required to support this hypothesis, together these small carbohydrates may alter bowel habits similar to polyols, as they contain the cyclic polyol scaffold as well. Thus classification of buckwheat flour-based products as low FODMAP foods is potentially debatable. Studies show that malting and germination can degrade the major fagopyritol, fagopyritol B1, in buckwheat and these treatments could represent effective ways to generate truly low-FODMAP products containing this cereal.
Thus although buckwheat is currently listed as a low FODMAP grain, a major portion of its soluble carbohydrate content is contributed by fagopyritols which are non-digestible, fermentable carbohydrates similar to GOS and could potentially act as a trigger for IBS symptoms. Moreover, large amounts of fagopyritols in buckwheat could increase the chance of small servings leading to symptoms. More studies are required to explore the fermentation and osmotic profile of fagopyritols and their potential effects on the sensitive gut to determine if they warrant classification as a new class of molecules in the FODMAP group.
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