Fructose is a sugar that occurs naturally in fruits, vegetables, and honey. When a person is unable to digest or absorb fructose, they may have fructose intolerance.
When a person has an intolerance to fructose, they may experience bloating, abdominal pain, and diarrhea.
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.
There are three different types of fructose intolerance.
Fructose malabsorption is a type of food sensitivity that affects 40% of those in the western hemisphere.
As with other food sensitivities, a combination of genetics, lifestyle factors, exposure to fructose, and overall health may play a part in causing it.
People with fructose malabsorption cannot properly absorb or digest fructose. As a result, fructose passes into the large intestine, causing gas and painful digestion.
Some people with fructose malabsorption have sensitivities to a group of foods that includes fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs).
FODMAPs include many types of both natural and artificial sweeteners.
Essential fructosuria, or hepatic fructokinase deficiency, is a harmless recessive disorder that a person may have without being aware of it.
If a condition is recessive, it means that a child will only have it if they receive the gene from both parents. If they receive the gene from one parent but not the other, they will be a carrier.
People with essential fructosuria lack a liver enzyme called hepatic fructokinase that can break down fructose.
Essential fructosuria is not harmful, and people with this condition are typically asymptomatic and do not need treatment.
Hereditary fructose intolerance
Hereditary fructose intolerance is a serious type of fructose intolerance. However, it is treatable and manageable.
It occurs when a person is unable to digest neither fructose nor fructose precursors, such as brown sugar.
Those with hereditary fructose intolerance lack sufficient activity of an enzyme called fructose-1-phosphate aldolase, which helps digest fructose.
The fructose then accumulates in the liver and kidneys, causing serious and potentially fatal complications, such as 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
The type of fructose intolerance will also determine how doctors treat or manage it.
People with fructose malabsorption should keep a food log and follow a low fructose diet.
Reducing fructose intake usually eases symptoms within about 2–6 weeks.
After symptoms improve, a person can gradually reintroduce foods to see how much fructose they can tolerate.
Typically, those with fructose malabsorption can consume 10–15g of fructose a day without experiencing symptoms.
Hereditary fructose intolerance
No treatment can cure hereditary fructose intolerance. Instead, a person should avoid consuming fructose.
As a fructose-free diet requires a person to avoid all fruits and numerous other foods, they may need support to eat a balanced, healthful diet and avoid nutritional deficiencies.
People with fructose malabsorption often get better by eating less fructose but not completely removing fructose from the diet.
However, people with hereditary fructose intolerance must eliminate fructose from their diet. To do this, they will need to avoid the following foods:
- 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 suspect that they have fructose malabsorption if they experience symptoms when they eat foods containing this sugar.
Some doctors may perform a breath test that can detect the levels of hydrogen in a person’s breath. A high level of hydrogen can indicate that a person has difficulty digesting fructose.
A doctor may also use the elimination diet to diagnose malabsorption. With an elimination diet, a person avoids all foods containing fructose and other potential allergens and then monitors the results.
A doctor can perform two diagnostic tests to determine whether a baby has hereditary fructose intolerance.
The first test is a liver biopsy, which can confirm a deficiency of aldolase, indicating a fructose intolerance. The second is a feeding test, during which a doctor delivers fructose via an intravenous needle and then assesses the body’s response to this sugar.
These methods may be dangerous, so a DNA test is a safer option. This test can suggest that a person may have fructose intolerance, and it is safer than traditional testing.
The causes and risk factors for the development of fructose malabsorption are unknown, but it appears to be more prevalent in young children.
According to a 2011 study, children between the ages of 1 and 5 years appeared to have a higher intolerance to fructose than those between the ages of 6 and 10 years.
For hereditary fructose intolerance, the risk factor involves genetics. A person may develop hereditary fructose by obtaining the gene from both of their parents.
A parent or caregiver may suspect that a child has hereditary fructose intolerance if there is a family history of the disease, or the child is frequently ill or has poor growth.
As this condition can be life threatening, it is important to seek prompt care from a specialist. A person should tell a doctor about any family history of genetic diseases.
People who think that they may have fructose malabsorption or a sensitivity can often treat the symptoms at home. They can try reducing the amount of fructose in their diet and monitor their symptoms.
If the symptoms do not improve, they should see a doctor who specializes in nutrition, allergies, or food intolerances.
Many people have fructose intolerance. Milder forms of the condition may cause discomfort and affect a person’s quality of life, but lifestyle changes can help.
If a person experiences any symptoms or is concerned that they are unable to tolerate fructose, they should seek treatment to relieve the symptoms and improve their quality of life.
Hereditary fructose intolerance may potentially be fatal without treatment.
If a parent or caregiver suspects that a child is unable to digest fructose, they should see a doctor without delay.