Dietary fructose intolerance, also known as fructose malabsorption, is the inability to absorb fructose in the small intestine. If you have this condition, consuming too much fructose can cause uncomfortable side effects like bloating, gas, constipation and/or diarrhea. Fructose is a simple sugar found in fruits, honey, corn syrup and as a component of table sugar. However, fructose also exists in a lesser-known form called fructans, found in wheat and some vegetables.
Malabsorption
The small intestine has a limited ability to absorb fructose as compared with its readily absorbed counterpart, glucose. The ability of humans to absorb free fructose varies greatly across populations. According to a 2007 article in "Practical Gastroenterology," up to 80 percent of people will not be able to completely absorb 50 g of fructose when ingested without the presence of other food. However, the ingestion of glucose along with fructose enhances its absorption. Therefore, complete elimination of fructose from the diet is not necessary if you have fructose malabsorption.
Sources
A 2006 review in the "Journal of the American Dietetic Association" describes the three forms fructose presents itself in the diet. First, free fructose exists in fruits and honey. A second source of fructose is as a component of sucrose or table sugar, a disaccharide made up of fructose and glucose. A third and frequently ignored source of fructose is fructans. Fructans are longer-chained oligosaccharides and polysaccharides of fructose that exist in some vegetables, such as onions and wheat.
Free Fructose
Not every food that contains fructose is a problem if you have fructose malabsorption. However, it is important to understand how fructose exists in different foods. For example, foods high in free fructose are problematic and need to be avoided. These include honey and fruits such as apples, pears, watermelon and papaya. Foods and drinks containing high fructose corn syrup, such as most sodas, corn syrup and/or fruit juice concentrate are also problematic. Glucose enhances fructose absorption in the gut, therefore, foods that contain sucrose or glucose in equal amounts to fructose are not considered problems. Most berries, citrus fruit and stone fruit, like apricots, nectarines and plums, contain glucose in balanced amounts, so they should be tolerable. Glucose-sweetened foods and drinks in moderation are also acceptable.
Fructans
Foods containing fructans may also be problematic and need to be limited. These include wheat-based foods such as flour, bread, pasta, cereals, baked goods and crackers. Onions, leeks, asparagus and Jerusalem artichoke also contain higher levels of fructans. Acceptable alternatives to wheat in moderate amounts are barley, rye flour, bread or crackers, gluten-free pastas and baked goods and rice. Garlic and lettuce are also fine. Unlike individuals who have celiac disease and require a completely gluten-free diet, those with fructose malabsorption can eat small amounts of wheat. Minor sources of fructans such as the wheat-based thickeners in commercially prepared foods do not typically pose a problem, says the American Dietetic Association review.
Hereditary Fructose Intolerance
An important distinction needs to be made between fructose malabsorption and hereditary fructose intolerance. According to the National Institutes of Health's MedlinePlus website, hereditary fructose intolerance is a disorder in which the body lacks an enzyme, aldolase B, necessary to break down fructose. Passed down through families, hereditary fructose intolerance manifests itself soon after a baby begins to consume formula or food. The symptoms are more severe and life-threatening. Complete removal of fructose and sucrose from the diet is essential.
References
- Nutrition Issues in Gastroenterology: Clinical Ramifications Of Malabsorption Of Fructose And Other Short-chain Carbohydrates
- Journal of the American Dietetic Association; Fructose Malaborption And Symptoms of Irritable Bowel Syndrome: Guidelines For Effective Dietary Management; Shepherd and Gibson; October 2006
- Medline Plus: Hereditary Fructose Intolerance
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