Hereditary fructose intolerance is a disease defined by an inability to properly metabolize fructose the an autosomal recessive disease caused by a lack of aldolase B. The disease may also be presented with the terms ALDOB deficiency, aldolase B deficiency, fructose aldolase B deficiency, fructose intolerance, fructose-1,6-biphosphate aldolase deficiency, fructose-1-phosphate aldolase deficiency and fructosemia.
The incidence of hereditary fructose intolerance is estimated to be 1 in 20,000 to 30,000 individuals each year worldwide. People with a more severe form of fructose intolerance called hereditary fructose intolerance will develop symptoms in infancy. Without treatment, they may develop life threatening complications, such as liver and kidney failure.
Fructose is a sugar that occurs naturally in fruits, vegetables, and honey. When people are unable to digest or absorb fructose, they may have fructose intolerance and this situation lead to experience bloating, abdominal pain, and diarrhea.
Patients are only symptomatic after eating fructose, so babies often present after eating fruit, juice, or honey. Symptoms also include vomiting, hypoglycemia, jaundice, and even eventual liver cirrhosis.
Working with a good dietitian who can support you in this process and develop a nutrition plan with you can be a good way to deal with hereditary fructose intolerance.
Fructose is a simple sugar, known as a monosaccharide, that makes up 50% of table sugar (sucrose) and it comes mostly from fruit and some vegetables. Table sugar also consists of glucose, which is the main energy source for your body’s cells. However, fructose needs to be converted into glucose by the liver before it can be used by the body.
It’s found in various sugary sweeteners; honey, agave nectar, and many processed foods that contain added sugars. If you see added sugar listed as one of its main ingredients in a product, you can be sure it contains high fructose.
After ingestion, fructose is converted to fructose-1-phosphate in the liver by fructokinase. Deficiencies of fructokinase cause essential fructosuria, a clinically benign condition characterized by the excretion of unmetabolized fructose in the urine. Fructose-1-phosphate is metabolized by aldolase B into dihydroxyacetone phosphate and glyceraldehyde. HFI is caused by a deficiency of aldolase B.
Aldolase B leads to the accumulation of fructose-1-phosphate, fructose-1-phosphate binds to free phosphate, thereby acting as a phosphate sink and depleting intracellular stores. After ingestion, fructose is converted to fructose-1-phosphate in the liver by fructokinase. Deficiencies of fructokinase cause essential fructosuria, a clinically benign condition characterized by the excretion of unmetabolized fructose in the urine. Fructose-1-phosphate is metabolized by aldolase B into dihydroxyacetone phosphate and glyceraldehyde. HFI is caused by a deficiency of aldolase B.
The build-up of unmetabolized fructose leads to its presence in the urine, which presents as a reducing sugar in the urine. Despite this, urine dipstick tests are negative, as they only test for the presence of glucose.
Fructose malabsorption is fairly common, affecting up to 1 in 3 people. Fructose carriers found in the enterocytes (cells in your intestines) are responsible for ensuring fructose is being directed to where it needs to go. If you have a deficiency of carriers, fructose can build up in your large intestine and cause gut issues.
Fructose malabsorption can be due to many causes that include:
Symptoms for fructose intolerance include:
- Abdominal pain
- Chronic fatigue
- Malabsorption of certain nutrients, such as iron
- A strong dislike of sweets
- Growth delays
- Impaired physical development
- Liver or kidney failure
In addition to gastrointestinal symptoms, there is evidence linking fructose malabsorption with mood disorders and depression. There are also scientific studies showing that fructose malabsorption is associated with low tryptophan levels, which plays a major role in the development of depressive disorders.
If symptoms are experienced while eating foods containing fructose, malabsorption may be suspected. Some doctors may perform a breath test, which can detect hydrogen levels in a patient’s breath. A high hydrogen level may indicate that the patient has difficulty digesting fructose.
Another method for diagnosing malabsorption is to follow an elimination diet. With an elimination diet, the person avoids all foods containing fructose and other potential allergens, and then the results are examined.
Two different diagnostic tests can be performed by physicians to determine if a baby has an inherited fructose intolerance. The first test is a liver biopsy, which can confirm aldolase deficiency, indicating a fructose intolerance. The second is a nutritional test in which the doctor administers fructose through an intravenous needle and then evaluates the body’s response to this sugar.
These methods can be dangerous, so DNA testing is a safer option. DNA testing may suggest that a person may have a fructose intolerance and is safer than conventional testing.
Treatment for HFI depends on the stage of the disease and the severity of symptoms. Stable patients without acute poisoning events are treated with careful dietary planning that excludes fructose and metabolic precursors. It is important to replace fructose with glucose, maltose or other sugars in the diet. Dietitians with extensive knowledge of what foods are acceptable play a major role in the management of HFI.
People with hereditary fructose intolerance should avoid certain foods to eliminate fructose from their diet. These foods include:
- Baked goods sorbitol, found in many candies and chewing gums fruit
- Fruit snacks
- Certain cereal bars
- Certain fruits, such as prunes, pears, cherries, peaches, apples, plums, and watermelon
- Apple juice and apple cider
- Pear juice
- Sugar snap peas
- Desserts such as ice cream, candy, and cookies containing fructose sweeteners
When reading labels, there are many ingredients to look out for when trying to manage fructose malabsorption. Be mindful of the following:
- High fructose corn syrup
- Agave nectar
- Crystalline fructose
- Fructooligosaccharides (FOS)
- Corn syrup solids
- Sugar alcohols