What is Fructose Intolerance?

Fructose intolerance, also known as hereditary fructose intolerance (HFI), is a genetic disorder characterized by the inability to metabolize fructose properly. It is caused by a deficiency of the enzyme aldolase B, which is responsible for breaking down fructose in the liver. Without adequate aldolase B activity, fructose cannot be properly metabolized, leading to a buildup of toxic substances in the body.

Here is a detailed discussion of fructose intolerance:

1. Genetic Basis: Fructose intolerance is an autosomal recessive disorder, meaning that an individual must inherit two copies of the defective gene (one from each parent) to develop the condition. The gene responsible for HFI is the ALDOB gene, which provides instructions for producing the enzyme aldolase B. Mutations in this gene result in reduced or absent aldolase B activity.
2. Metabolic Process: In individuals with fructose intolerance, the metabolism of fructose is impaired. Normally, fructose is converted into fructose-1-phosphate by the action of aldolase B. Fructose-1-phosphate is then further broken down into intermediates that can enter the glycolytic pathway or be used for energy production. However, in HFI, the deficiency of aldolase B results in the accumulation of fructose-1-phosphate, leading to metabolic disturbances.
3. Clinical Presentation: The symptoms of fructose intolerance typically manifest when fructose or sucrose (which is composed of fructose and glucose) is consumed. Infants may show symptoms when introduced to fruits, fruit juices, or foods containing fructose or sucrose. Common symptoms include:
   • Severe abdominal pain and bloating
   • Nausea and vomiting
   • Hypoglycemia (low blood sugar)
   • Jaundice (yellowing of the skin and eyes)
   • Generalized weakness and fatigue
   • Failure to thrive (poor growth and development)
   • Irritability

   If left untreated, fructose intolerance can lead to serious complications such as liver and kidney damage.

4. Diagnosis: Fructose intolerance can be diagnosed through various tests, including genetic testing to identify mutations in the ALDOB gene. Additionally, a fructose tolerance test may be conducted, where the individual is given a specific amount of fructose, and blood samples are taken to measure fructose-1-phosphate levels.
5. Management and Treatment: The primary treatment for fructose intolerance is the strict avoidance of fructose and sucrose in the diet. This involves eliminating foods and beverages that contain fructose, such as fruits, honey, table sugar, and high-fructose corn syrup. Individuals with fructose intolerance may need to work closely with a registered dietitian to develop a suitable dietary plan that ensures adequate nutrition while avoiding fructose-containing foods.

   In cases of acute symptoms or severe reactions, medical intervention may be required to manage hypoglycemia and provide supportive care.

It’s important to note that fructose intolerance is different from fructose malabsorption, which is a more common condition where the intestines have difficulty absorbing fructose. Fructose malabsorption typically leads to gastrointestinal symptoms but does not involve the same metabolic disturbances as fructose intolerance.

If you suspect fructose intolerance, it is recommended to consult with a healthcare professional for proper diagnosis and guidance on dietary management.