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|Classification and external resources|
|Classification and external resources|
Fructose malabsorption, formerly named "dietary fructose intolerance," 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 in the entire intestine.
Occurrence in patients identified to be suffering symptoms of irritable bowel syndrome is not higher than occurrence in the normal population. However, due to the similarity in symptoms, patients with fructose malabsorption often fit the profile of those with irritable bowel syndrome. A small proportion of patients with both fructose malabsorption and lactose intolerance also suffer from celiac disease.
Fructose is absorbed in the small intestine without help of digestive enzymes. Even in healthy persons, however, only about 25–50g of fructose per sitting can be properly absorbed. People with fructose malabsorption absorb less than 25g per sitting. In the large intestine, fructose that has not been adequately absorbed reduces the absorption of water osmotically and is metabolized by colonic bacteria into short chain fatty acids, producing the byproduct gases hydrogen, carbon dioxide and methane. This abnormal increase in hydrogen is 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; they have a higher chance of inducing symptoms in people with functional gut disorders than asymptomatic subjects. Some effects of fructose malabsorption are decreased tryptophan, folic acid and zinc in the blood.
Xylose isomerase acts to convert fructose sugars into glucose. Dietary supplements are limited in the amount of fructose they can convert, thus the amount of fructose in a meal must be estimated and an appropriate dosage taken to work.
Foods that should be avoided by people with fructose malabsorption include:
Foods with a high glucose content ingested with foods containing excess fructose may help sufferers absorb the excess fructose.
The role that fructans play in fructose malabsorption is still under investigation. However, it is recommended that fructan intake for fructose malabsorbers should be kept to less than 0.5 grams/serving, and supplements with inulin and fructooligosaccharide (FOS), both fructans, should be avoided.
According to the USDA database, foods with more fructose than glucose include:
|Food||Fructose (grams / 100 grams)||Glucose (grams / 100 grams)|
The USDA food database reveals that many common fruits contain nearly equal amounts of the fructose and glucose, and they do not present problems for those individuals with fructose malabsorption. Some fruits with a greater ratio of fructose than glucose are apples, pears and watermelon, which contain more than twice as much fructose as glucose. Fructose levels in grapes varies depending on ripeness and variety, where unripe grapes contain more glucose.
The following list of favorable foods was cited in the paper: "Fructose malabsorption and symptoms of Irritable Bowel Syndrome Guidelines for effective dietary management". The fructose and glucose contents of foods listed on the Australian food standards would appear to indicate that most of the listed foods have higher fructose levels.
Producers of processed food in most or all countries, including the USA, are not currently required by law to mark foods containing "fructose in excess of glucose." This can cause some surprises and pitfalls for fructose malabsorbers.
Foods (such as bread) marked "gluten-free" are usually suitable for fructose malabsorbers, though sufferers need to be careful of gluten-free foods that contain dried fruit or high fructose corn syrup or fructose itself in sugar form. However, fructose malabsorbers do not need to avoid gluten, as those with celiac disease must.
Many fructose malabsorbers can eat breads made from rye and corn flour. However, these may contain wheat unless marked "wheat-free" (or "gluten-free") (Note: Rye bread is not gluten-free.) Although often assumed to be an acceptable alternative to wheat, spelt flour is not suitable for sufferers of fructose malabsorption, just as it is not appropriate for those with wheat allergies or celiac disease. However, some fructose malabsorbers do not have difficulty with fructans from wheat products while they may have problems with foods that contain excess free fructose.
There are many breads on the market that boast having no high fructose corn syrup. In lieu of high fructose corn syrup, however, one may find the production of special breads with a high inulin content, where inulin is a replacement in the baking process for the following: high fructose corn syrup, flour and fat. Because of the caloric reduction, lower fat content, dramatic fiber increase and prebiotic tendencies of the replacement inulin, these breads are considered a healthier alternative to traditionally prepared leavening breads. Though the touted health benefits may exist, sufferers of fructose malabsorption will likely find no difference between these new breads and traditionally prepared breads in alleviating their symptoms because inulin is a fructan, and, again, consumption of fructans should be reduced dramatically in those with fructose malabsorption in an effort to appease symptoms.
Fructose and fructans which are polymers of fructose are FODMAPs (Fermentable Oligo-, Di- and Mono-saccharides and Polyols) known to cause gastrointestinal discomfort in susceptible individuals. A low FODMAP diet has widespread application for managing functional gastrointestinal disorders such as IBS.