Fructose Malabsorption ............................................................................................................................. 3 Introduction .............................................................................................................................................. 3 Metabolism .............................................................................................................................................. 4 Fructose Malabsorption ......................................................................................................................... 5 Diagnosis ................................................................................................................................................. 6 Diet ........................................................................................................................................................... 7 Fructose Malabsorption: A Possible Factor in Functional Bowel Disorders ........................... 7 Functional Bowel Disorders .............................................................................................................. 8 Fructose Malabsorption ..................................................................................................................... 8 ................................................................................................................................................................ 10 Pathophysiology of Fructose Malabsorption ............................................................................. 10 Assessment of Dietary Fructose Intake ....................................................................................... 10 Fructose Malabsorption in IBS ....................................................................................................... 11 Fructose-Restricted Diet .................................................................................................................. 11 Role of the Pharmacist ..................................................................................................................... 11 REFERENCES ..................................................................................................................................... 12 Fructose malabsorption .......................................................................................................................... 14 Pathophysiology ................................................................................................................................... 14 Symptoms .............................................................................................................................................. 15 Diagnosis ............................................................................................................................................... 15 Treatment .............................................................................................................................................. 15 Xylose isomerase ............................................................................................................................. 15 Diet ..................................................................................................................................................... 15 Dietary guidelines for the management of fructose malabsorption[edit].................................. 17 Food-labeling ........................................................................................................................................ 17 New research ......................................................................................................................................... 18 See also .................................................................................................................................................. 18 References ............................................................................................................................................. 18 Use and abuse of hydrogen breath tests .............................................................................................. 19 Abstract .................................................................................................................................................. 19 Hydrogen breath tests ......................................................................................................................... 20 Carbohydrate malabsorption .............................................................................................................. 21 Carbohydrate digestion and absorption ........................................................................................ 21 Lactose malabsorption .................................................................................................................... 21 Fructose malabsorption ................................................................................................................... 23 Small intestinal bacterial overgrowth ................................................................................................. 24 Normal bowel flora ........................................................................................................................... 25 Definition of SIBO ............................................................................................................................. 25 Tests for SIBO .................................................................................................................................. 26 Is there a link between SIBO and IBS? ........................................................................................ 28 Conclusion ............................................................................................................................................. 29 Abbreviations ........................................................................................................................................ 29 Footnotes ............................................................................................................................................... 29 References ............................................................................................................................................ 29 FOFMAPs to the rescue…………………..38 Fructose Malabsorption Fructose malabsorption is a digestive disorder in which the absorption capacity of the sugar fructose in the small intestine is reduced. This leads to an increase of fructose in the large intestine where the sugar is degraded by intestinal bacteria to several chemical compounds which will then cause symptoms like bloating, wind, abdominal pain, diarrhea and/or constipation. Introduction The natural occurrence of fructose as a monosaccharide (molecular fructose) is mainly in fruits and vegetables. It is also a component of the disaccharide sucrose, the table sugar, which is composed of one molecule glucose and one molecule fructose. Molecular fructose is sweeter than glucose and is therefore often used as sweetener in pastries, sweets and sodas. The average daily intake of fructose has increased dramatically over the last 40 years mainly due to the increased usage of this High Fructose Corn Syrup (HFCS) as a sweetener. Fig. 1:Sucrose (Disaccharid) Fig. 2:Molecular Fructose (Monosaccharid) Fructose is absorbed in the small intestine via the GLUT-5 transporter. This transport from the intestinal lumen into the enterocytes, the intestinal absorptive cells, is passive and driven by the concentration difference of fructose between the intestinal lumen and the plasma of the cells. The capacity of this transport system is limited and varies greatly between individuals. About 40% of the population show signs of malabsorption after a single dose of 25g of fructose, a dosis far below the average daily intake which is estimated to be around 70g per day. Sorbitol, a sugar alcohol which is widely used as sugar substitute in industrial foods, further reduces the fructose absorption capacity by binding to the GLUT-5 transporter. Concomitant consumption of glucose with a fructose-rich meal can increase the absorption capacity of fructose which is why most of patients suffering from fructose malabsorption tolerate table sugar quite well. It is believed that this effect may be due to an increased integration of the GLUT-2 transporter into the membrane of the enterocytes. GLUT-2 acts as a passive transporter for glucose, galactose and fructose with low affinity (that means it only transports these sugars if their concentration is high). This transporter is only integrated into the membrane after a meal when the sugar concentration in the intestine is high. This detection of sugar in the intestinal lumen only works with glucose and therefore a fructose-rich meal will not trigger this integration of GLUT-2. Metabolism Unlike glucose fructose can only be utilized by a few cells of the body directly. Most of the absorbed fructose is transported to the liver where it is phosphorylated and converted into fat, glucose or energy (figure 3). Currently there is an ongoing discussion whether fructose may induce obesity and non-alcoholic fatty liver disease. Until now there is no hard evidence to support this thesis as most studies investigating this effect yielded conflicting results. But considering the differences between fructose and glucose metabolism it is a reasonable conclusion: