Fructose intolerance

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at January 2, 2017
StartDiseasesFructose intolerance

Fructose intolerance can describe several distinct conditions where the digestive system is unable to process and absorb fructose properly. It can be a genetic disorder or it can be idiopathic, that is, not have a definite cause.


Definition & Facts

Fructose is found in food and drink, especially fruits, juices that come from fruit, certain vegetables, and honey. Fructose can also be found in table sugar as well as high-fructose corn syrup, which is used in processed, sweetened products.

Hereditary fructose intolerance is a very serious and life-threatening condition that results from genetic mutations affecting the production of a liver enzyme responsible for metabolizing fructose. 1 in 20,000 to 30,000 are affected by hereditary fructose intolerance.

Fructose malabsorption is a different and far less severe condition where the small intestine cannot absorb fructose. This undigested fructose is taken into the colon where intestinal flora break it down. Unpleasant and painful side effects ensue. Up to 40 percent of the global population has fructose malabsorption.

While some people only experience symptoms when large quantities of fructose are ingested, others experience symptoms when even the slightest amount of fructose is ingested. It is estimated that a third of patients with irritable bowel syndrome have fructose intolerance or malabsorption. Irritable bowel syndrome affects up to 30 percent of the population worldwide.

Symptoms & Complaints

The symptoms of fructose intolerance vary, depending on the severity of the condition. They can include generalized stomach pain, cramps, bloating, nausea, abdominal distension, constipation, and diarrhea.

In some cases, heartburn, headaches, dizziness, and depression may be present as well. Intestinal inflammation can also occur.

Symptoms of hereditary fructose intolerance include intellectual disability, convulsions, and jaundice (the yellowing of the skin and whites of the eyes or sclera).


Hereditary fructose intolerance results from a mutation of the ALDOB gene which produces aldolase B, an enzyme that breaks down fructose. Fructose builds up in the liver which causes liver cells to die. It is inherited in an autosomal recessive pattern.

Fructose malabsorption is largely idiopathic, that is, its causes are unclear. Many patients report experiencing severe stress around the time the first symptoms appeared. There may also be an association with abnormal gut bacteria and excessive consumption of foods containing fructose.

Diagnosis & Tests

The diagnostic process involves physical examinations as well as an intake of the patient's medical history and family history. An enlarged spleen (splenomegaly) or liver (hepatomegaly) may indicate hereditary fructose intolerance. Blood tests, liver function tests, and clinical urine tests may also be performed, and blood sugar tests will reveal hypoglycemia or low blood sugar.

Fructose malabsorption can be diagnosed through breath tests. These tests are completed by recommending the patient fast for between eight and 12 hours. Fructose that is not broken down completely, or that is not completely absorbed, releases hydrogen and methane into the mouth and respiratory system. The level of hydrogen and methane in the breath are monitored at recommended intervals every few hours.

Treatment & Therapy

Treatment for fructose malabsorption and hereditary fructose intolerance focuses on reducing or eliminating the ingestion of fructose. Treatment involves developing an understanding of the various foods that contain fructose which can trigger symptoms. Since glucose assists in the digestion of fructose, consuming foods that contain equal amounts of both, like strawberries, allows the fructose to bind to glucose molecules, creating an easier way for it to enter the intestines. Seeking professional medical advice allows patients to develop a better understanding of the foods that can be eaten safely.

Prevention & Prophylaxis

The advice of a genetic counselor may be sought by prospective parents to assess the risk that their offspring may be born with the genetic mutation that causes hereditary fructose intolerance. People who have a family history of the disorder should be tested to see if they have the disorder or if they are a genetic carrier of the disorder.

Managing stress, treating chronic inflammation, taking measures to ensure a healthy amount of bacteria in the gut, and monitoring the amount of fructose in one’s diet can reduce the risk of developing fructose malabsorption in adulthood.