Fructose malabsorption is presumably due to a defective transport mechanism in the small intestine. The specific transport protein responsible for the absorption of fructose is inoperative owing to hereditary or external factors so that fructose is not absorbed and reaches the colon. This results mainly in two complaints: a. water accumulates through osmosis in the small intestine causing diarrhoea because this surplus liquid cannot be absorbed in the colon, and b. fructose is decomposed in the colon by bacteria forming short-chain fatty acids and gases, and this causes complaints such as flatulence, bloating, abdominal pain and headache. Fructose malabsorption is often wrongly diagnosed, as irritable bowel syndrome (IBS), just like other kinds of carbohydrate malabsorptions.
Fructose malabsorption can be diagnosed simply and painlessly by the Hydrogen Breath Test (HBT). Great care should be taken, however, if somebody is suspected of suffering from HFI because the Hydrogen Breath Test can be extremely risky in this case, see below.
At the moment there is no cure for fructose malabsorption. People suffering from it should maintain a low-fructose or, in severe cases, fructose-free diet.
More information about the various kinds of sugar/sugars please see sugars.