Correction
02/11/10 05:06 AM
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Syl
Reged: 03/13/05
Posts: 5499
Loc: SK, CANADA
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Excess fructose is a relative notion. For a person with fructose malabsorption an excess amount can mean that a food containing as little a couple of grams of excess fructose (i.e. a couple of grams more fructose than glucose) can cause problems. Normally a person with or with or IBS can handle more than 25 grams of excess fructose. Usually a 25 gram load of fructose is used to diagnose fructose malabsorption which is about the amount of excess fructose found in a soft drink sweetened with HFCS. At 50 grams almost everyone exhibits fructose malabsorption. As pointed out previously up to 50% of IBS-C and IBS-D can exhibit fructose malabsorption.
Quote:
In patients with fructose malabsorption, the small intestine fails to absorb fructose properly. This results in excess hydrogen caused by an overgrowth of otherwise normal intestinal bacteria.
This is incorrect. It is true that fructose cannot be absorbed properly in the small intestine but there is little evidence that it is caused by an overgrowth of bacteria except in the case of SIBO or that the problem is particularly hydrogen gas. However, there is some evidence that individuals that truly have SIBO may have more problems with excess fructose that clears up when the SIBO is treated. Most bacteria in the colon can digest sugars especially those in the beginning part of the large intestine producing hydrogen, carbon dioxide or methane. The later gas possibly being responsible for C.
This is the way it is described by experts on fructose malabsorption (references below)
Quote:
Fructose and fructans are fermented by bacteria, yielding short-chain fatty acids (SCFA) and the gases, hydrogen, carbon dioxide and, in some, methane. Observations in vitro using faecal slurries and in vivo using breath hydrogen testing indicate that fructose and fructans are rapidly fermented by bacteria. It is probable, therefore, that such substrates are totally fermented in the very proximal large bowel and possibly distal small intestine, and that subsequent rapid gas formation might distend the lumen locally before the gas is absorbed or further metabolized.
Quote:
Failure to completely absorb fructose in the small intestine (that is, fructose malabsorption) leads to its delivery to the colonic lumen, together with water due to its osmotic effect. Luminal bacteria rapidly ferment fructose to hydrogen, carbon dioxide, and short-chain fatty acids. Thus, if sufficient fructose reaches the colon, luminal distention may occur due to the osmotic load and rapid gas production, which potentially leads to bloating, abdominal discomfort, and motility changes.
One thing I learned in graduate school and I always tell my students is to check the original sources because many times secondary contain errors. 
While not all IBSers have fructose malabsorption in those that do which could be up to 50% of the IBS population excess fructose is serious IBS trigger and should be treated like other IBS triggers -- with caution! When you live with this problem like I do you get to intimately know the details of having IBS and fructose malabsorption
References
Gibson, P. R., Newham, E., Barrett, J. S., Shepard, S. J., & Muir, J. G. (2007). Review article: fructose malabsorption and the bigger picture . Alimentary Pharmacology & Therapeutics, 25(4), 349-363
Shepherd, S. J., & Gibson, P. R. (2006). Fructose Malabsorption and Symptoms of Irritable Bowel Syndrome: Guidelines for Effective Dietary Management . Journal of the American Dietetic Association, 106(10), 1631-1639
Parrish, C. R. (2007). Malabsorption of Fructose and Other Short-chain Carbohydrates . Practical Gastroenterology
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