Fructose is a sugar that occurs naturally in fruits, vegetables, and honey. When a person cannot 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 types of fructose intolerance.

Fructose malabsorption

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 correctly 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 types of both natural and artificial sweeteners.

Essential fructosuria

Essential fructosuria, or hepatic fructokinase deficiency, is a harmless recessive disorder that a person may have without knowing.

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. 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 cannot digest fructose and fructose precursors such as brown sugar.

Those with hereditary fructose intolerance lack sufficient activity of an enzyme that helps digest fructose called fructose-1-phosphate aldolase, according to work from 2007.

The undigested fructose accumulates in the liver and kidneys. This may lead to serious and even life threatening complications such as liver failure and kidney failure.

The symptoms that a person experiences may depend on the type of fructose intolerance.

Fructose malabsorption

Fructose malabsorption may cause:

Hereditary fructose intolerance

Hereditary fructose intolerance is present at birth, which means that most babies will experience symptoms when they begin eating solid foods.

Without treatment or lifestyle changes, it may be life threatening.

Symptoms include:

  • a strong dislike of sweets
  • growth delays
  • vomiting
  • jaundice
  • impaired physical development
  • hyperventilation
  • liver or kidney failure

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The type of fructose intolerance will also determine how doctors treat or manage it.

Fructose malabsorption

People with fructose malabsorption should keep a food log and follow a low fructose diet.

Reducing fructose intake typically eases symptoms within about 2–6 weeks, according to 2014 research.

After symptoms reduce, a person can gradually reintroduce foods to determine how much fructose they can tolerate.

Typically, those with fructose malabsorption can consume 10–15 grams 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, nutritious diet.

People with fructose malabsorption often find their symptoms ease by eating less fructose but not completely removing fructose from their 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 includes many processed items such as soda and prepackaged baked goods
  • sorbitol, which is present in many candies and gums
  • fruit
  • 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 through an IV needle. They then assess 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 three types of fructose intolerance are as follows.

Fructose malabsorption

Fructose malabsorption may result from inflammation or damage to the small intestine that prevents it from fully absorbing fructose, meaning fructose remains in the gastrointestinal tract.

The risk factors for fructose malabsorption include the following, all of which can affect the intestines:

  • Celiac disease: Although this autoimmune disease mainly involves the malabsorption of gluten, a small study found that 7 out of 30 people with celiac disease also showed fructose malabsorption.
  • Inflammatory bowel disease (IBD): Crohn’s disease and ulcerative colitis may cause inflammation of the small intestine, leading to the malabsorption of fructose and other important nutrients.
  • Irritable bowel syndrome (IBS): In a study of 31 children and adolescents with this chronic gastrointestinal disorder or abdominal pain, researchers found fructose malabsorption in 9 of the 10 participants with IBS. Those with fructose malabsorption also had a higher body mass index.
  • Acute gastroenteritis: Commonly known as stomach flu, this intestinal infection may cause inflammation as well as malabsorption of fructose and other nutrients.
  • High fructose diet: Consuming large amounts of products made with high fructose corn syrup overwhelms the small intestine’s ability to absorb fructose and significantly reduces the production of beneficial intestinal bacteria, according to one small study.
  • Stress: Mental stress can affect the gastrointestinal tract. Nearly 40% of people with IBS have significantly increased anxiety and depression.
  • Antibiotics: A study found that some antibiotics alter microorganisms in the gut, increasing the risk of IBD.

Hereditary fructose intolerance

This serious condition results from the liver’s insufficient production of the enzyme aldolase B due to mutations in the ALDOB gene.

If both parents have the mutated ALDOB gene, each child has a 25% risk factor for developing hereditary fructose intolerance.

Essential fructosuria

Essential fructosuria (hepatic fructokinase deficiency) is a lack of hepatic fructokinase, a liver enzyme that breaks down fructose.

As with hereditary fructose intolerance, it is an autosomal recessive disorder, meaning the risk factor comes from both parents with the mutated gene passing the genes to the child.

A parent or caregiver may suspect that a child has hereditary fructose intolerance if there is a family history of the disease, the child is frequently ill, or the child has less growth than expected.

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 they may have fructose malabsorption or sensitivity to fructose can often treat symptoms at home. They can try reducing the amount of fructose in their diet and monitoring their symptoms.

If symptoms do not ease, they may wish to contact a doctor who specializes in nutrition, allergies, or food intolerances.

What are the signs of fructose intolerance?

While some people with fructose malabsorption or intolerance may not experience symptoms, common signs include intestinal issues such as pain, gas, bloating, diarrhea, and nausea.

What are the foods to avoid if you are fructose intolerant?

People with fructose malabsorption should follow a low FODMAP diet that avoids high fructose foods such as products made with high fructose corn syrup and fruits such as apples and grapes. This comes from research from 2014.

People with hereditary fructose intolerance must completely eliminate fructose from their diets.

Can you suddenly develop fructose intolerance?

Hereditary fructose intolerance and essential fructosuria are inherited conditions that don’t develop suddenly. Fructose malabsorption may develop from conditions that affect the intestines, such as acute gastroenteritis, IBD, or a high fructose diet.

What happens if you are fructose intolerant?

With fructose malabsorption or essential fructosuria, a person may have symptoms that ease with diet changes. Hereditary fructose intolerance must be treated by a doctor, because it can be life threatening.

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 cannot tolerate fructose, they should seek treatment to relieve symptoms and improve their quality of life.

Hereditary fructose intolerance may be life threatening without treatment.

If a parent or caregiver suspects that a child cannot digest fructose, they should contact a doctor without delay.