What Is Fructose Intolerance?

Medically Reviewed by Dan Brennan, MD on September 14, 2023
3 min read

Fructose is a natural sugar that’s found in fruit, some veggies, and honey. Certain people can’t absorb fructose properly. This is called fructose intolerance. The two kinds of fructose intolerances are dietary and hereditary.

Hereditary fructose intolerance is a genetic disorder. Your body lacks the necessary protein or enzyme that’s needed to break down fructose when you have fructose intolerance. That means your body can’t digest the fructose found in many different foods.

‌Causes. This kind of fructose intolerance happens when you have an enzyme called aldolase B that isn’t working. This enzyme is in your liver and helps turn fructose into usable energy. You have a 25% chance of developing hereditary fructose intolerance if both of your parents have the gene that causes aldolase B not to work.

If you eat foods that have fructose or sucrose, another kind of sugar, your body can’t change stored sugar into glucose. This causes your blood sugar to crash and toxins can build up in your liver.

Symptoms. Most people with this inherited form of fructose intolerance start showing signs as a baby. New cases are rarely diagnosed in adults. Infants often have symptoms of intolerance as soon as they are introduced to foods that contain fructose. Some common symptoms include:

  • Jaundice
  • Stunted growth
  • Vomiting
  • Bloating
  • A decrease of phosphate and glucose in the blood
  • An increase in fructose in the urine and blood
  • Nausea
  • Abdominal pain
  • Dislike of fruit or sweet things

Hereditary fructose intolerance can be dangerous. Undigested fructose can build up in your body. It can then damage both your liver and kidneys. Other serious effects include seizures, coma, and even organ failure.

Some other serious complications associated with hereditary fructose intolerance are:

The other kind of fructose intolerance is called dietary fructose intolerance. This is also known as fructose malabsorption. and occurs when the cells in your intestines simply can’t break down fructose in the food that you eat.

Cause. Our bodies have a limit on how much fructose we can take in and digest. This limit varies from person to person. Your body’s ability to absorb fructose can also be affected by:

Fructose malabsorption develops when you’re an adult. This is one of the differences between the two types of fructose intolerance.

Symptoms. Malabsorbed fructose refers to fructose that hasn’t been digested completely. It ferments in your lower bowels. You may experience symptoms similar to those of irritable bowel syndrome (IBS) when you eat foods with a lot of fructose, such as:

  • Bloating
  • Gas
  • Diarrhea
  • Stomachaches

Your doctor may perform several tests to diagnose hereditary fructose intolerance. These tests are done on infants when they start to show symptoms. Some tests that can confirm this condition are:

Your baby will also have a physical examination. Your doctor might check to see if the spleen or liver are larger than normal or if your baby is jaundiced.

Diagnosing dietary fructose intolerance is more challenging. Your doctor might have to try a few different tests since the symptoms are similar to other conditions.

The best test for diagnosing fructose intolerance is the breath test. In this test, you drink a solution that has fructose dissolved into it. The amount of methane and hydrogen you breathe out then helps to show if you’re digesting the fructose properly or not.

You should avoid foods and drinks that have high amounts of fructose if you have fructose intolerance. Fructose is found in fruits. High-fructose corn syrup is a sweetener that’s used in many different products.

You should avoid the following foods:

  • Sweeteners like agave, honey, high-fructose corn syrup, maple syrup, molasses, and palm or coconut sugar
  • Fruit juices
  • High-fructose fruit like apples, grapes, watermelon, and tomatoes
  • High-fructose vegetables like peas, asparagus, zucchini, artichokes, leeks, okra, mushrooms, and bell peppers
  • Soda

Try to bring fruits and veggies into your diet that fall on the low end of the fructose spectrum. For example:

  • Citrus fruits like lemons, limes, and oranges
  • Avocados
  • Berries like strawberries, blueberries, and cranberries
  • Bananas
  • Lettuce
  • Green beans
  • Cantaloupe

Limiting your intake of fructose can be difficult since it eliminates so many fruits and vegetables. To make sure that you’re getting adequate nutrition, you can work with a dietician or specialist. 

The good news is that you can greatly reduce your fructose intolerance symptoms by lowering how much fructose you eat.