Fructose malabsorption
Fructose malabsorption or Dietary Fructose Intolerance is a dietary disability of the small intestine in which the fructose carrier in enterocytes is deficient.

# 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 ].

# Pathophysiology
Fructose Malabsorption is not to be confused with  Hereditary Fructose Intolerance (HFI), a hereditary 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. 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. 

# 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.

# Symptoms
This condition is common in patients with symptoms of Irritable Bowel Syndrome. A small proportion of patients with both fructose malabsorption and lactose intolerance also suffer from celiac disease.
Typical symptoms of fructose malabsorption include:
- Bloating
- 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

# Foods of concern

## Foods with high fructose content
According to the USDA database  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,. 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
- Green beans
- 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  and supplements with inulin and fructooligosaccharide (FOS), fructans, intake should be avoided.

## 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  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.