Fructose is a naturally occurring sugar in nuts, vegetables, and honey. When a person can not digest or consume fructose, he or she may have allergy to fructose.
If a person has fructose intolerance, they can experience bloating, abdominal pain, and diarrhea.
People with a more severe form of exposure to fructose called inherited intolerance to fructose will develop symptoms at infancy. They can cause life-threatening problems, such as hepatic and kidney failure, without medication.
Types of fructose intolerance
There are three different types of fructose intolerance.
Malabsorption of fructose is a form of food sensitivity that affects 40 percent of western hemisphere people.
As with other sensitivities of food, a combination of genetics, lifestyle factors, fructose intake and overall health can play a role in causing it.
People with malabsorption of fructose can not take up or digest fructose properly. Fructose moves into the large intestine resulting in gas and painful digestion.
Many people with malabsorption of fructose have sensitivity to a food group that includes fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP).
FODMAPs contain several forms of natural as well as artificial sweeteners.
Critical fructosuria, or deficiency in hepatic fructokinase, is a harmless recessive condition that a person can experience without being aware of.
If a disease is recessive it means a child will have it only if both parents obtain the gene. If one parent but not the other receives the gene, they’ll be a carrier.
People with critical fructosuria lack a hepatic fructokinase enzyme that can break down fructose.
Essential fructosuria is not dangerous and usually people with this condition are asymptomatic and do not need medication.
Hereditary fructose intolerance
Inherited intolerance to fructose is a severe sort of intolerance to fructose. It’s treatable and manageable, however.
It occurs when a person can not digest precursors of either fructose or fructose, such as brown sugar.
An enzyme called fructose-1-phosphate aldolase, which helps digest fructose, is missing for those with inherited fructose intolerance.
Fructose then builds up in the liver and kidneys, causing severe and potentially fatal problems including liver and kidney failure.
The symptoms that a person experiences may depend on the type of fructose intolerance.
Fructose malabsorption may cause:
Hereditary fructose intolerance
Hereditary fructose intolerance is present at birth, which means that most babies will have symptoms when they begin eating solid foods.
Without treatment or lifestyle changes, it may be life threatening.
- a strong dislike of sweets
- growth delays
- impaired physical development
- liver or kidney failure
Treatment and management
The type of fructose intolerance will also determine how doctors treat or manage it.
Persons with malabsorption of fructose can keep a food log and adopt a low intake of fructose.
Reducing the consumption of fructose usually relieve the symptoms within 2-6 weeks.
A person should slowly reintroduce foods after symptoms improve, to see how much fructose they can handle.
Those with malabsorption of fructose usually will eat 10–15 g of fructose a day without symptoms.
Hereditary fructose intolerance
No treatment can remedy resistance to the inherited fructose. A person should avoid taking fructose instead.
Since a fructose-free diet allows a person to avoid all the fruits and many other foods, they may need help to eat a full, healthy diet and prevent nutritional deficiencies.
Foods to avoid
Persons with malabsorption of fructose often get better by eating less fructose but not eliminating fructose from the diet entirely.
People with genetic deficiency to fructose must however remove fructose from their diet. They’ll need to stop the following foods to do this:
- any foods and beverages containing high fructose corn syrup, which include many processed items, such as soda and prepackaged baked goods
- sorbitol, which is present in many candies and gums
- fruit-sweetened snacks
A person may be suspected of having malabsorption of fructose if they experience symptoms when eating foods containing that sugar.
Some doctors can conduct a breath test which can measure hydrogen levels in a person’s breath. High hydrogen levels may mean a person has trouble digesting fructose.
A doctor may also treat malabsorption using the elimination diet. A person eliminates all foods containing fructose and other possible allergens with an elimination diet, and then tracks the effects.
A doctor will conduct two diagnostic tests to determine if a baby has an inherited sensitivity to fructose.
The first examination is a liver biopsy that can confirm an aldolase deficiency, suggesting an allergy to fructose. The second is a feeding test where a doctor delivers fructose through an intravenous injection and then tests the reaction of the body to this sugar.
Such techniques are potentially dangerous, so a DNA test is a safer option. This test may indicate a person may have intolerance to fructose, and is safer than conventional testing.
The causes and risk factors for the occurrence of fructose malabsorption are unclear but in young children it tends to be more prevalent.
According to a 2011 report, children aged 1 to 5 years seemed to have a higher susceptibility to fructose than those aged 6 of 10 years.
The risk factor for inherited resistance to fructose includes genetics. A person can develop inherited fructose by having the gene from both parents.
When to see a doctor
A parent or caregiver may believe that a child has inherited fructose intolerance if the disease has a family history, or the child is often sick, or has poor development.
It is important to seek prompt treatment from a specialist as this condition can be life-threatening. Any family history of genetic diseases should be reported to a doctor.
People who think they may have a malabsorption of fructose or a deficiency can often treat the symptoms at home. They can try to reduce their daily amount of fructose and control their symptoms.
If the symptoms do not change, a doctor who specializes in diet, allergies or food intolerance should be seen.
Most individuals do have resistance to fructose. Mild types of the condition can cause discomfort and affect the quality of life of a person but changes in lifestyle can improve.
If a person has any symptoms or is worried that they can not tolerate fructose, they will seek treatment to ease the symptoms and improve the quality of their life.
Genetic intolerance to fructose could potentially be fatal without treatment.
If a parent or caregiver thinks a child can’t digest fructose, they should see a doctor immediately.