Evidence-based Dietary Management of Functional Gastrointestinal Symptoms: The FODMAP Approach

Peter R Gibson; Susan J Shepherd

Disclosures

J Gastroenterol Hepatol. 2010;25(2):252-258. 

In This Article

More Than Just Fructose and Fructans

Lactose is a disaccharide naturally-occurring in mammalian milk, including that from cows, sheep and goats. Human digestion of lactose requires the enzymic action of lactase to hydrolyse the disaccharide to its constituent monosaccharides, glucose and galactose, which are then readily absorbed. As recently reviewed,[29] the activity of lactase is deficient in a proportion of adults and children, varying with ethnicity. Malabsorption of lactose (which can be detected by breath hydrogen testing, a lactose tolerance test, or lactase activity associated with small bowel biopsy) indicates that lactose should be considered a FODMAP in that individual.

Legumes, including lentils, chickpeas, and red kidney beans, are significant dietary sources of galactans. Vegetarians often consume large amounts of galactans due to increased consumption of legumes—these are commonly utilized as an important source of protein in the vegetarian diet, particularly those following vegan vegetarian diets. Also, people consuming cuisines that are based on these foods, such as dahl, many curries and soups from the Indian sub-continent, and chilli con carne and refried beans from Mexico, are also likely to have a greater intake of galactans.

Polyols are relatively underexplored as FODMAPs but are found widely in foods. Polyols do not have associated active transport systems in the small intestine and are probably absorbed by passive diffusion. The rate of absorption is related to three factors. First, the diffusion occurs through 'pores' in the epithelium and therefore depends upon molecular size.[30] For example, erythritol, a 4-carbon polyol, is well-absorbed in the jejunum but mannitol, a 6-carbon polyol, is not.[31] Secondly, there is variation of pore size along the small intestine with larger pores proximally. Thus, erythritol is less well-absorbed in the ileum.[32] The rapidity of transit through the jejunum will therefore influence the degree of absorption. Finally, pore size is affected by mucosal disease; pore size reduces in celiac disease where erythritol is poorly absorbed.[32] It is not surprising then that limited studies performed on the absorption of sorbitol and mannitol have yielded considerable individual variation and that the amount available for fermentation varies with dose taken.[33,34] Polyols are present in food (for example, sorbitol is often found in food rich in free fructose, mannitol is found in mushrooms) and are used as artificial sweeteners, being identified by the following additive numbers on food packages: sorbitol (420), xylitol (967), mannitol (421), maltitol (965), and isomalt (953). Sorbitol has also been marketed as a laxative and warnings have been placed on candies, especially sugarless chewing gum, that polyols used as an artificial sweetener can have a laxative effect.

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