Fructose malabsorption

Fructose malabsorption or Dietary Fructose Intolerance is a digestive disorder^[1] of the small intestine in which the fructose carrier in enterocytes is deficient. As a result of this problem, the concentration of fructose in the entire intestine is increased. Fructose malabsorption is found in approximately 30-40% of the population of Central Europe, with about half of the affected individuals exibiting symptoms.^[2]

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Diagnosis

Medical tests are similar as in lactose intolerance, requiring a hydrogen breath test for a clinical diagnosis.

It can be associated with reduced plasma tryptophan^[3] and clinical depression.

Pathophysiology

Fructose Malabsorption is not to be confused with Hereditary Fructose Intolerance (HFI), a condition in which the liver enzymes that break up fructose are deficient. In patients with fructose malabsorption, the small intestine fails to absorb fructose properly. In the large intestine the unabsorbed fructose 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. The abnormal increase in hydrogen is detected 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 patients with functional gut disorders than asymptomatic subjects. Some effects of fructose malabsorption are decreased tryptophan, folic acid^[4] and zinc in the blood.^[5] Restricting dietary intake of free fructose and/or fructans may have durable symptomatic benefits in a high proportion of patients with functional gut disorders, but high quality evidence is lacking.^[6]

Treatment

There is no known cure, but an appropriate diet will help. However, it is very difficult for undiagnosed sufferers to see any relationship between the foods they eat and the symptoms they suffer, even if they keep a daily diet diary. This is because most foods contain a mixture of fructose and glucose. Foods with more fructose than glucose are a problem. However, depending upon the sufferer's sensitivity to fructose, small amounts of problem foods could be eaten (especially when they are not the main ingredient of a meal).

Foods with a high glucose content actually help sufferers absorb fructose.^[7]

Symptoms

This condition is common in patients with symptoms of Irritable Bowel Syndrome and most patients with fructose malabsorption fit the profile of those with Irritable Bowel Syndrome.^[8] A small proportion of patients with both fructose malabsorption and lactose intolerance also suffer from celiac disease. Dr. De Meirlier has found that 45% of his patients with Chronic Fatigue Syndrome suffer from fructose malabsorption and 10% suffer from lactose intolerance.

Typical symptoms of fructose malabsorption include:

• Bloating (because of fermentation in the small and large intestine)
• Diarrhea and / or constipation
• Flatulence
• Stomach pain (due to muscle spasms, which can vary from mild and chronic to acute but erratic)

Other possible symptoms of fructose malabsorption include:

• Aching eyes
• Fuzzy head
• Fatigue
• Depression^[9] as a result of absorption disorders in the small and large intestines, other substances such as amino acids are not absorbed. Because of missing substances (among others tryptophan), hormones and neurotransmitters cannot be synthesized.

Foods of concern

Foods with high fructose content

According to the USDA database,^[10] foods with more fructose than glucose include:

There is a lot of misinformation and misconception about fruit sugar content. A common belief is that fruits contain mainly, or only, fructose sugar. The USDA food database reveals that many common fruits contain nearly equal amounts of the fructose and glucose.^[11] There is a tendency within plants to keep these sugars 50/50. The only aberrantly high fructose fruits are apple and pear, which have twice as much fructose as glucose. Fructose levels in grapes varies with ripeness and variety, with unripe grapes containing 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 malabsorber should be kept to less than 0.5 grams/serving^[12] and supplements with inulin and fructooligosaccharide (FOS), fructans, intake should be avoided.^[12]

Other problem foods

In addition, the following foods can cause symptoms of fructose malabsorption:

• Sodas and other beverages containing high fructose corn syrup
• Dried fruit (including "health" bars containing dried fruit)
• Tinned fruit in "natural" juice (which is often pear juice)
• Sorbitol (present in some diet drinks and foods, and occurring naturally in some stone fruits)
• Sweet wines
• Too much fruit of any kind in a short timeframe

Dietary Guidelines for the Management of Fructose Malabsorption

Dietary guidelines^[12] 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, apricot, currant, date, fig, pear, prune, raisin, sultana
• Fruit juices
• Fruit pastes - chutney, relish, plum sauce, sweet & sour sauce, BBQ sauce.
• Coconut
• Dried fruit bars
• Honey
• Fortified wines
• HFCS
• Corn syrup solids
• Fruit juice concentrates

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

• Stone fruit: apricot, nectarine, peach, plum (caution - these fruit contain sorbitol)
• Berry fruit: blueberry, blackberry, boysenberry, cranberry, raspberry, strawberry
• 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 do those with celiac disease.

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 malabsorber do not have difficulty with fructans from wheat products while they may have problems with foods that contain excess free fructose.^[6]

See also

• Gastroenterology
• Invisible disability
• Glucose-galactose malabsorption
• German Wikipedia article on fructose malabsorption -- Google Translate

References

• 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.

• www.fructose.at

• ME/CFS and Chronic Infection of the Gut – Notes on Dr. Kenny De Meirleir’s Presentation in Perth