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 fructose intolerance, 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 childhood. Without treatment, they can develop life-threatening complications, such as liver and kidney failure.
Types of fructose intolerance
There are three different types of fructose intolerance.
Fructose malabsorption is a type of food sensitivity that affects 40% of people in the Western Hemisphere. As with other food sensitivities, a combination of genetics, lifestyle factors, exposure to fructose, and general health can all contribute to 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 food group that includes fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs). FODMAPs include many types of natural and artificial sweeteners.
Essential fructosuria, or hepatic fructokinase deficiency, is a harmless recessive disorder that a person can have without realizing 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 from the other, they will be carriers.
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 generally 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 or fructose precursors, such as brown sugar. People with inherited fructose intolerance lack sufficient activity of an enzyme called fructose-1-phosphate aldolase, which helps digest fructose. Fructose then accumulates in the liver and kidneys, causing serious and potentially fatal complications, such as liver and kidney failure.
Symptoms of fructose intolerance
The symptoms a person experiences may depend on the type of fructose intolerance.
Fructose malabsorption can cause:
Hereditary fructose intolerance symptoms
Hereditary fructose intolerance is present at birth, which means that most babies will have symptoms when they start eating solid foods. Without treatment or lifestyle changes, it can be fatal.
- A strong aversion to sweets
- Stunted growth
- Impaired physical development
- Liver or kidney failure
Treatment and management of fructose intolerance
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 your fructose intake generally relieves symptoms in about 2 to 6 weeks. After symptoms improve, a person can gradually reintroduce food to see how much fructose they can tolerate. Generally, people with fructose malabsorption can consume 10-15 g of fructose per day without experiencing symptoms.
Hereditary fructose intolerance treatment
No treatment can cure hereditary fructose intolerance. Instead, a person should avoid consuming fructose. Since a fructose-free diet requires a person to avoid all fruits and many other foods, they may need support to eat a healthy, balanced diet and avoid nutritional deficiencies.
Foods to avoid when having fructose intolerance
People with fructose malabsorption often improve by eating less fructose but not completely eliminating fructose from the diet. However, people with an inherited fructose intolerance should eliminate fructose from their diet. To do this, they will need to avoid the following foods:
- Any food and drink that contains high fructose corn syrup, including many
- Processed items, such as soda and baked goodsprepackaged
- Sorbitol, which is present in many sweets and gums
- Fruit-sweetened snacks
Fructose intolerance diagnosis
A person may suspect fructose malabsorption if they experience symptoms when eating foods that contain this sugar. Some doctors can perform a breath test that can detect hydrogen levels in a person’s breath. A high level of hydrogen can indicate that a person has difficulty digesting fructose. A doctor can also use the elimination diet to diagnose malabsorption. With an elimination diet, a person avoids all foods that contain fructose and other potential allergens and then monitors the results. A doctor can perform two diagnostic tests to determine if a baby has an inherited fructose intolerance.
The first test is a liver biopsy, which can confirm an aldolase deficiency, indicating a fructose intolerance. The second is a feeding test, during which a doctor administers fructose through an IV needle and then assesses the body’s response to this sugar.
These methods can 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 tests.