Fructose malabsorption

Fructose malabsorption, formerly named dietary fructose intolerance (DFI), is a digestive disorder in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose. Intolerance to fructose was first identified and reported in 1956. Similarity in symptoms means that patients with fructose malabsorption often fit the profile of those with irritable bowel syndrome. Fructose malabsorption is not to be confused with hereditary fructose intolerance, a potentially fatal condition in which the liver enzymes that break up fructose are deficient. Hereditary fructose intolerance is quite rare, affecting up to 1 in 20,000 to 30,000 people. Fructose malabsorption may cause gastrointestinal symptoms such as abdominal pain, bloating, flatulence or diarrhea. Fructose is absorbed in the small intestine without help of digestive enzymes. Even in healthy persons, however, only about 25–50 g of fructose per sitting can be properly absorbed. People with fructose malabsorption absorb less than 25 g per sitting. Simultaneous ingestion of fructose and sorbitol seems to increase malabsorption of fructose. Fructose that has not been adequately absorbed is fermented by intestinal bacteria producing hydrogen, carbon dioxide, methane and short-chain fatty acids. This abnormal increase in hydrogen may be detectable with the hydrogen breath test. The physiological consequences of fructose malabsorption include increased osmotic load, rapid bacterial fermentation, altered gastrointestinal motility, the formation of mucosal biofilm and altered profile of bacteria. These effects are additive with other short-chain poorly absorbed carbohydrates such as sorbitol. The clinical significance of these events depends upon the response of the bowel to such changes. Some effects of fructose malabsorption are decreased tryptophan, folic acid and zinc in the blood. Restricting dietary intake of free fructose and/or fructans may provide symptom relief in a high proportion of patients with functional gut disorders.