Introduction
Fructose malabsorption, also known as 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 in the entire intestine.
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. 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.
Signs and symptoms of fructose malabsorption
- Bloating
- Diarrhea and/or constipation
- Heartburn
- Stomach pain
- Vomiting
- Early signs of mental depression
- Nausea
Diagnosis
The diagnostic test for fructose malabsorption is called a hydrogen breath test
Treatment
There is no known cure, but an appropriate diet and the enzyme xylose isomerase can help. 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
- Foods and beverages containing greater than 0.5 g fructose in excess of glucose per 100 g and greater than 0.2 g of fructans per serving should be avoided. Foods with >3 g of fructose per serving are termed a ‘high fructose load’ and possibly present a risk of inducing symptoms. However, the concept of a ‘high fructose load’ has not been evaluated in terms of its importance in the success of the diet.
- Foods with high fructose-to-glucose ratio. Glucose enhances absorption of fructose, so fructose from foods with fructose-to-glucose ratio <1, like white potatoes, are readily absorbed, whereas foods with fructose-to-glucose ratio >1, like apples and pears, are often problematic regardless of the total amount of fructose in the food. Foods rich in fructans and other fermentable oligo-, di- and mono-saccharides and polyols (FODMAPs), including artichokes, asparagus, leeks, onions, and wheat-containing products, including breads, cakes, biscuits, breakfast cereals, pies, pastas, pizzas, and wheat noodles.
- Foods containing sorbitol, present in some diet drinks and foods, and occurring naturally in some stone fruits, or 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.
- Foods containing High fructose corn syrup.
Dietary guidelines for the management of fructose malabsorption
Unfavourable foods
- Fruit – apple, pear, guava, honeydew melon, nashi pear, pawpaw, papaya, quince, star fruit, watermelon;
- Dried fruit – apple, currant, date, fig, pear, raisin, sultana;
- Fortified wines
- Foods containing added sugars, such as agave nectar, some corn syrups, and fruit juice concentrates.
Favourable foods
- Stone fruit: apricot, nectarine, peach, plum (caution — these fruits contain sorbitol);
- Berry fruit, blackberry, boysenberry, cranberry, raspberry, strawberry, loganberry;
- Citrus fruit: kumquat, grapefruit, lemon, lime, mandarin, orange, tangelo;
- Other fruits: ripe banana, jackfruit, passion fruit, pineapple,
References
Gibson, P.R. (2007). Review article: fructose malabsorption and the bigger picture. Aliment. Pharmacol. Ther. 25 (4): 349–63
Ledochowski, M. & Fuchs, D. (2001). Fructose malabsorption is associated with decreased plasma tryptophan. Scand. J. Gastroenterol. 36 (4): 367–71.
Skoog, S.M. & Bharucha, A.E. (2004). Dietary fructose and gastrointestinal symptoms: a review. Am. J. Gastroenterol. 99 (10): 2046–50.
Tabarrok, A. (2010 Jan. 8th). The Meat Market. Wall Street Journal.
