Fructose Malabsorption (or non-hereditary Fructose Intolerance)
Fructose malabsorption is fairly common, affecting up to 1 in 3 people. It is just as common in people with a diagnosis of irritable bowel syndrome as in the rest of the population, and symptoms are quite similar but generally triggered by intake of fructose – containing foods. In some cases, fructose malabsorption may be caused by diseases which cause intestinal damage, such as celiac disease.
Fructose malabsorption is not to be confused with “hereditary fructose intolerance (HFI)” a rare, potentially fatal condition in which the liver enzymes that break up fructose are deficient.
Fructose malabsorption may cause gastrointestinal symptoms such as abdominal pain, bloating, flatulence and diarrhea.
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. Simultaneous ingestion of fructose and sorbitol seems to increase the malabsorption of fructose. Fructose that has not been adequately absorbed is fermented by intestinal bacteria producing hydrogen, methane and carbon dioxide, as well as short-chain-fatty-acids. This abnormal increase in hydrogen may be detectable with the hydrogen and methane breath tests with fructose as a substrate.
As a result of fructose malabsorption, rapid bacterial fermentation in the small intestine occurs, leading to altered gastrointestinal motility (e.g. diarrhea), the formation of mucosal biofilms, and a change in the intestinal flora. These effects are additive if other poorly absorbed carbohydrates are present, such as sorbitol. The clinical significance of these events depends upon the individual susceptibility to such changes. There is also evidence that fructose malabsorption can cause decreased Tryptophan, Folic Acid and Zinc levels in the blood.
Restricting dietary intake of free fructose and/or fructans (longer sugars containing fructose) may provide symptom relief in a high proportion of patients with such functional gut disorders.
One has to be careful with the results of the Fructose Breath Test, because a negative result does not completely rule out that a trial of fructose restriction may help the patient (in other words, the sensitivity of the test is relatively low), while a positive result is very specific that such a trial is useful.
Sorbitol is a sugar alcohol that is found in many types of fruit and vegetables, where it serves as a precursor for sugar synthesis. We consume it in small quantities with our food all the time. This substance belongs to the group of FODMAPs, i. e. carbohydrates that are poorly absorbed by the body.
Because it usually only occurs in small amounts in natural food, our intestinal system is naturally not prepared to digest high quantities of sorbitol. Most sugar alcohols like sorbitol have a highly laxative effect even for healthy people – with doses of 20-50 grams the majority of people will develop diarrhea.
However, if you experience digestive problems after consuming only a few grams, you might suffer from sorbitol sensitivity or intolerance.
The problem is much larger than meets the surface, given that sorbitol and other sugar alcohols are commonly used in the food industry, since they absorb water and thus prevent the dehydration of packaged food. This is how products like packaged cakes stay fluffy and moist. The same ingredients also work as sugar replacements in diabetic and some sugar-free or sugar-reduced foods, because they don’t cause the blood sugar level to rise. Hence, these products are popular with diabetics and “weight watchers”.
Common natural foods containing sorbitol:
Apples, pears, apricots, plums, peaches cherries, dried fruit
Common processed foods containing significant amounts of sorbitol:
Chocolate, Cream Fillings, Cough drops, Chewing gum, Ginger bread, packaged cakes (including cupcakes, muffins etc), Icecream, chewy fruit candies, jams and marmalade, and many sugar-free products. Also medications can contain some sorbitol.
Depending on the consumed dose symptoms of intolerance can range from minor flatulence, belly ache and loose stools to severe diarrhea.
The reason for this lies in the hygroscopic (water-attracting) effect of sugar alcohols: If large amounts of undigested sugar alcohols reach the colon, they cause an unpleasant sequence of events. Sorbitol draws water from its environment, increasing the stool volume. The intestinal bacteria ferment the unabsorbed sorbitol, often producing harmful metabolic products and digestive gases, which further irritates the GI tract. The symptoms are quite similar to other carbohydrate malabsorptions, like lactose intolerance.
There are multiple studies that have shown sorbitol-induced nonspecific abdominal symptoms and diarrhea in a significant number of adults, with diabetics slightly more commonly afflicted than non-diabetics. In some studies up to 20-35% of adults will develop symptoms after ingestion of only 10g of Sorbitol. These symptoms, when not properly diagnosed as sorbitol-intake-related, could lead to an extensive diagnostic work-up and a lifelong (erroneous) diagnosis of irritable bowel syndrome.
A Sorbitol Breath Test can diagnose this condition. — The sorbitol breath test is easy to do and non-invasive, and there is generally a good correlation between the severity of symptoms and the amount of hydrogen/methane exhaled.
One problem exists with proper interpretation, however: In some healthy people an intake of only 5 grams per day (that is the equivalent of 5 sugar-free candies or 4-5 sticks of sugar-free gum) can already lead to abnormalities (with a positive test and/or symptoms). Intake of 10 grams per day has been shown to produce positive test results in a significant number of people, with symptoms in 20-35%. 20 grams cause abnormalities in over 80%. Nobody generally tolerates large amounts of sorbitol. THEREFORE: a positive test result on the breath test is only relevant if consumption of sorbitol-containing foods also lead to similar symptoms. The individual interpretation has to be done in the context of the patient’s symptoms and associated diet.
Regardless of the test result the patient should keep a detailed record of their diet and check if symptoms disappear by avoiding sorbitol. If that is not the case, the health care provider should reexamine the diagnosis and look for additional or other explanations. One possibility is that there is also fructose malabsorption. Since sorbitol in the intestine inhibits fructose uptake, the symptoms of sorbitol consumption can worsen if there is fructose malabsorption. In addition, the body converts sorbitol to fructose. Therefore, Fructose Breath Testing in addition to Sorbitol Breath Testing may be useful in some cases.