Fructose malabsorption

Fructose Malabsorption
Classification and external resources
File:Beta-D-Fructofuranose.svg Fructose
ICD-10	E74.3
ICD-9	271
OMIM	138230

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.

Fructose malabsorption is found in approximately 30-40% of the population of Central Europe, with about half of the affected individuals exhibiting symptoms resembling irritable bowel syndrome.

This condition is common in patients identified to be suffering symptoms of irritable bowel syndrome, although occurrence in these patients is not higher than occurrence in the normal population. Conversely, 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 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.

Pathophysiology

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. Persons with fructose malabsorption may absorb less than 25g per sitting (NB: Amount is arbitrarily determined according to investigation of fructose absorption in many individuals). In the large intestine, fructose that hasn't been adequately absorbed osmotically reduces the absorption of water and is metabolized by normal colonic bacteria to short chain fatty acids and the 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 increasing osmotic load, providing substrate for rapid bacterial fermentation, changing gastrointestinal motility, promoting mucosal biofilm and altering the 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.

Restricting dietary intake of free fructose and/or fructans may provide symptom relief in a high proportion of patients with functional gut disorders, but quality evidence may be lacking.

Symptoms

• Bloating (from fermentation in the small and large intestine)
• Diarrhea and/or constipation
• Flatulence
• Stomach pain (as a result of muscle spasms, the intensity of which can vary from mild and chronic to acute but erratic)
• Vomiting (if great quantities are consumed)
• Early signs of mental depression

Diagnosis

The diagnostic test, when used, is similar to that used to diagnose lactose intolerance. It is called a hydrogen breath test and is the method currently used for a clinical diagnosis. When a breath test cannot be performed, a stool test may be used.

Treatment

There is no known cure, but an appropriate diet will help.

Diet

Foods that should be avoided by people with fructose malabsorption include:

• Foods and beverages containing greater than 0.5g fructose in excess of glucose per 100g, greater than 3g fructose in an average serving quantity regardless of glucose intake and greater than 0.2g of fructans per serving.
• Fructose consumed in large quantities
• Foods with high fructose-to-glucose ratio (NB: Glucose enhances absorption of fructose, so fructose from foods with fructose-to-glucose ratio <1, like bananas, are readily absorbed, while foods with fructose-to-glucose ratio >1, like apples and pears, are often problematic regardless of total amount of fructose in the food
• Foods rich in fructans and other Fermentable Oligo-, Di- and Mono-saccharides and Polyols (FODMAPs)
• Foods rich in sorbitol
• Foods such as high fructose corn syrup (HFCS) or honey

Foods with a high glucose content ingested with foods containing excess fructose may help sufferers absorb the excess fructose.

Foods with high fructose content

According to the USDA database, foods with more fructose than glucose include:

Food	Fructose (grams / 100 grams)	Glucose (grams / 100 grams)
Sucrose (for reference)	50	50
Apples	5.9	2.4
Pears	6.2	2.8
Fruit juice e.g. Apples, Pears	5 to 7	2 to 3
Watermelon	3.4	1.6
Raisins	29.8	27.8
Honey	40.9	35.7
High fructose corn syrup	55 to 90	45 to 10

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.

Foods with high fructan content

Chains of fructose molecules known as fructans occur naturally in many foods. The following foods have a high fructan content:

• Artichokes
• Asparagus
• Leeks
• Onions including spring onion
• Wheat including most beers, breads, cakes, biscuits, breakfast cereals, pies, pastas, pizzas, and some noodles

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.

Other problem foods

In addition, the following foods should also be avoided:

• Sorbitol (present in some diet drinks and foods, and occurring naturally in some stone fruits)
• Xylitol present in some berries, and other polyols (sugar alcohols), such as erythritol, mannitol, and other ingredients that end with -tol, commonly added as artificial sweeteners in commercial foods.
• Any processed foods or foods prepared by others containing the foods listed above
  • For example:
    • Sodas and other beverages containing high fructose corn syrup (HFCS)
    • Dried fruit (including "health" bars containing dried fruit)
    • Tinned fruit in "natural" juice (often, this is pear juice)
    • Sweet wines

Dietary guidelines for the management of fructose malabsorption

Dietary guidelines have been developed for managing fructose malabsorption particularly for individuals with IBS.

Unfavorable foods (i.e. more fructose than glucose)

• Fruit — apple, pear, guava, honeydew melon, nashi fruit, pawpaw, papaya, quince, star fruit, watermelon
• Dried fruit - apple, currant, date, fig, pear, raisin, sultana
• Honey
• Fortified wines
• High Fructose Corn Syrup - many processed products contain this
• Corn syrup solids
• Fruit juice concentrates
• Agave nectar
• Red Ripe Tomato

Favorable foods (i.e. fructose equal to or less than glucose)

• Stone fruit: apricot, nectarine, peach, plum (caution - these fruits contain sorbitol)
• Berry fruit: blueberry, blackberry, boysenberry, cranberry, raspberry, strawberry, loganberry
• Citrus fruit: kumquat, grapefruit, lemon, lime, mandarin, orange, tangelo
• Other fruits: ripe banana, jackfruit, kiwi fruit, passion fruit, pineapple, rhubarb, tamarillo

Food-labelling laws

Producers of processed food 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.

Note that 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.

Note that 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.

New research

A low FODMAP diet is now sufficiently evidenced for efficacy, and its widespread application in conditions such as IBS and IBD is recommended. Restriction of Fermentable Oligo-, Di- and Mono-saccharides and Polyols globally, rather than individually, controls the symptoms of functional gut disorders (e.g. IBS), and the majority of IBD patients respond just as well. For those who suffer from fructose malabsorption, a low FODMAP diet may be more successful than restricting only fructose and fructans, as is currently recommended. Compliance to the diet is high.

See also

• Gastroenterology
• Hydrogen breath test
• Invisible disability
• Food intolerance
• Irritable bowel syndrome
• Malabsorption

External links

• Fructose Malabsorption -- Practical Gastroenterology
• Low FODMAP Diet
• Ledochowski M, Widner B, Bair H, Probst T, Fuchs D (2000). "Fructose- and sorbitol-reduced diet improves mood and gastrointestinal disturbances in fructose malabsorbers". Scand. J. Gastroenterol. 35 (10): 1048–52. doi:10.1080/003655200451162. PMID 11099057. CS1 maint: Multiple names: authors list (link)
• Ledochowski M, Uberall F, Propst T, Fuchs D (1999). "Fructose malabsorption is associated with lower plasma folic acid concentrations in middle-aged subjects". Clin. Chem. 45 (11): 2013–4. PMID 10545075. CS1 maint: Multiple names: authors list (link)

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