Fructose intolerance, also known as fructose malabsorption, is caused by an inability to completely absorb dietary fructose due to a decreased amount of the enzyme sucrase-isomaltase (SI) in the small intestine.
When this enzyme is not present in sufficient quantities, undigested fructose reaches the colon, where it is metabolized by the colonic flora and can cause symptoms such as abdominal distention, excessive gas production, and diarrhea.
The most common food sources of fructose are table sugar (sucrose) and high-fructose corn syrup (HFCS); fruits and vegetables also contain fructose but in much smaller amounts. Patients with fructose intolerance need to avoid fructose and sucrose altogether, while small quantities of HFCS are often well absorbed.
Symptoms of fructose intolerance
Various symptoms may indicate fructose intolerance; these symptoms occur due to increased intestinal permeability and osmotic load. Symptoms include:
- Flatulence (passing gas)
- Abdominal bloating, pain, or discomfort (especially after consuming sucrose or fructose)
- Loose stools or diarrhea
It is important to note that someone with fructose intolerance might not have all the symptoms, and the severity of symptoms may vary for each individual.
Diagnosing fructose intolerance
The most common method for assessing intestinal fructose absorption is administering an oral glucose tolerance test (OGTT). During an OGTT, a patient drinks a 75g solution of glucose or sucrose in water or juice, then measured for blood sugar at the patient’s fasting state.
The patient then drinks a second solution of water or juice containing 75g of fructose; this is measured 10 and 120 minutes later to see if symptoms appear. If symptoms do not occur after the first drink (glucose), they are likely to not happen after the second drink (fructose), meaning that fructose is not absorbed in the small intestine.
If symptoms do occur, they are likely to be milder when compared with glucose because at least some of the ingested glucose reached the colon.
Causes of fructose intolerance
An enzyme deficiency in the small intestine is believed to cause fructose intolerance. In healthy individuals, absorption of fructose occurs via a specific carrier-mediated transport system where a substance called fructose-specific IIBC (fructose transporter) transports fructose across the intestinal epithelium and into the enterocytes.
In people with fructose intolerance, this carrier-mediated transport system is not present in sufficient quantities, which results in undigested fructose reaching the colon.
Treatment for fructose intolerance
Fructose malabsorption can be treated by altogether avoiding foods containing fructose and sucrose.
Smaller quantities of HFCS are often well absorbed, but it still may be best to avoid this as well; it’s best to check with your physician or dietician regarding the fructose content of any foods consumed.
Patients with fructose intolerance should look at food labels for ingredients that contain fructose, sucrose, and HFCS; these include:
- Honey, molasses, brown sugar
- High-fructose corn syrup
- Agave syrup
- Sorghum and molasses
- Fruit juice concentrates
- “Healthy” yogurts containing these ingredients as well as others
Also, artificial sweeteners such as aspartame may contain fructose. It is best to avoid these products if you have fructose intolerance. An easy way to do this is to eat more whole foods and avoid processed ones.
Fructose intolerance can be managed by avoiding the problematic ingredients listed above, but it cannot be cured alone with medication or diet therapy.
Leave a Reply