What Is Fructose Intolerance?

Fructose is a sugar found in fruit, vegetables, and sweeteners. The amount of fructose people consume has increased over recent years, and it could be behind your stomach problems. While you may have heard of people needing to go gluten-free or having a lactose intolerance, some people have fructose intolerance.

This article will discuss the types of fructose intolerance, including causes and risk factors. Also learn symptoms, diagnosis, and how to manage this condition.

What Is Fructose?

Fructose is one of the naturally occurring sugars. It’s found in fruit, some vegetables, and honey.

Fructose is a simple sugar, like glucose. But unlike glucose, fructose isn’t directly used as energy. Instead, your small intestine and liver convert fructose into glucose so it can be stored and used for energy.

Most people can easily convert fructose to glucose without problems. However, some people can develop an intolerance to fructose, making it difficult for their bodies to metabolize (break down) fructose properly.

Types and Causes of Fructose Intolerance

There are two types of fructose intolerance. One is caused by a genetic issue that leaves your body unable to convert fructose to glucose. The other develops if there is too much fructose in your diet. 

Hereditary Fructose Intolerance

Hereditary fructose intolerance is caused by a mutation in the aldolase B gene. It’s a rare condition estimated to affect somewhere between 1 out of every 18,000 to 30,000 people.

People with hereditary fructose intolerance are usually diagnosed once they are weaned from breastmilk or formula to fructose-containing solid foods, like fruit puree. However, because some infant formulas contain fructose, symptoms could develop earlier.  

In some cases, a person won’t be diagnosed with this condition until they’re older because their symptoms remain controlled by avoiding fructose-containing foods.

When someone with this condition eats fructose, the fructose builds up in the body and causes health problems, such as blood sugar crashes and liver damage. 

Dietary Fructose Intolerance

Dietary fructose intolerance isn’t caused by a genetic mutation. Researchers are still working to understand the exact causes of this condition. It may be due to fructose malabsorption (the cells in your small intestine can’t fully break down and absorb fructose) or how fructose affects the friendly microbes that inhabit the digestive tract.

Fructose intolerance appears to be affected both by the amount of fructose in your diet and digestive diseases like:

• Inflammatory bowel diseases, like Crohn’s disease or ulcerative colitis
• Irritable bowel syndrome (a functional gastrointestinal disorder)
• Celiac disease (an autoimmune disease triggered by dietary gluten)

Dietary fructose intolerance is more likely to develop when you’re an adult. The amount of fructose a person can tolerate will vary. 

Tests and Diagnosis

Diagnosing a fructose intolerance is challenging because it’s rare, and the symptoms are similar to other conditions. The types of tests used to diagnose a fructose intolerance depend on the type.

Hereditary Fructose Intolerance

A hereditary intolerance can be slightly easier to diagnose, especially in infants, since foods are usually introduced slowly. If an infant frequently experiences symptoms and aversions to fructose-containing foods, it may indicate this intolerance.

Genetic testing for abnormalities in the aldolase B gene is the best test to confirm hereditary fructose intolerance. Other tests that may be used include:

• Liver biopsy (a tissue sample is taken and analyzed in the lab)
• Liver enzyme tests (blood tests looking for specific proteins)
• Blood sugar tests
• Urinalysis (a urine sample is analyzed in the lab)

When an adult is diagnosed with hereditary fructose intolerance, they typically have a history of avoiding sweets, fruits, and other fructose foods.

Dietary Fructose Intolerance

Diagnosing dietary fructose intolerance can be more challenging because the symptoms are similar to other conditions and food intolerances. Therefore, your healthcare provider may need to run several tests and rule out other conditions before you receive a diagnosis.

A food journal can help with the diagnosis because it helps you understand if there are any links between specific foods and when symptoms develop.

The best test for diagnosing fructose malabsorption is a breath test. During a breath test, the amount of methane and hydrogen in your breath is measured before and after drinking a fructose-containing beverage. The change in methane and hydrogen helps show how well your body is digesting fructose.

Symptoms

The symptoms and potential complications of hereditary fructose intolerance include:

• Nausea and vomiting
• Bloating
• Abdominal pain
• Aversion or dislike of sweet foods
• Stunted growth
• Jaundice (yellowing of the skin and eyes)
• Liver damage
• Kidney damage
• Seizures (uncontrolled electrical activity in the brain)
• Coma
• Organ failure

The common symptoms of dietary fructose intolerance include:

• Bloating
• Gas
• Diarrhea
• Abdominal pain
• Nausea

Management

It’s recommended for people with hereditary fructose intolerance to avoid consuming any fructose-containing foods. One case study reported a woman developed symptoms after consuming one sip of a sweetened beverage.

People with dietary fructose intolerance should follow a low-fructose diet. The exact amount of fructose they can consume without developing symptoms will vary. It’s best to try to avoid any high-fructose foods and add in foods low in fructose.

Usually, the symptoms of fructose intolerance can be well managed by eating habits. 

Foods to Avoid

It’s recommended to avoid foods high in fructose. These include the following.

Fruits:

• Most fruits like apples, watermelon, grapes, mangoes 
• Fruit juices
• Dried fruits like prunes, raisins, or dates
• Fruit purees like applesauce
• Fruits canned in juice or syrup
• Fruit jams or jellies

Vegetables:

• Artichoke
• Broccoli
• Leeks
• Mushrooms
• Okra
• Onions
• Peas
• Red pepper
• Shallots
• Tomatoes and tomato products

Other foods:

• Foods and beverages sweetened with high fructose corn syrup
• Meats marinated and seasoned with fructose foods
• Sugars like sucrose (table sugar), honey, agave, molasses, syrup

Low-Fructose Fruits and Vegetables

Here are some fruits and vegetables low in fructose that may be tolerated by those with dietary fructose intolerance.

Fruits:

• Bananas
• Cranberries
• Kiwi
• Lime
• Mandarin oranges
• Pineapple
• Strawberries

Vegetables:

• Carrots
• Celery
• Chives
• Green peppers
• White potatoes
• Winter squash

When to See a Healthcare Provider

If you’re experiencing any of the symptoms of fructose intolerance, it’s best to contact your healthcare provider. The symptoms of fructose intolerance are similar to other health conditions, so it’s important to get a diagnosis to know the exact cause.

Your healthcare provider will also help you develop a treatment plan or refer you to a registered dietitian to help you follow a low-fructose diet. 

Summary

Fructose intolerance is a condition where the body can’t properly digest and metabolize fructose. It can be caused by a genetic mutation or develop for other reasons.

Hereditary fructose intolerance is usually diagnosed with a genetic test to assess the aldolase B gene. Dietary fructose intolerance is generally diagnosed with a breath test after ingesting fructose. 

Symptoms can include bloating, nausea, vomiting, diarrhea, abdominal pain, yellowish skin, and organ damage. Fructose intolerance is treated by following a low fructose diet and avoiding high-fructose foods like most fruits, fruit juices, some vegetables, and sweeteners. 

A Word From Verywell

It can feel daunting to be diagnosed with a condition like fructose intolerance because it eliminates many foods. Still, limiting your fructose can help ease your symptoms, and you’ll still be able to enjoy many delicious foods. Consider meeting with a dietitian to help you create a plan that works for you and still meets your nutrition needs.