Fructose Malabsorption

How fructose is absorbed

Fructose is absorbed in the small intestine by transport proteins, mainly GLUT5. Their capacity is limited. When fructose is eaten with glucose in roughly equal amounts, as in table sugar, absorption is better. When fructose exceeds glucose ("excess fructose"), as in apples, pears, honey and high-fructose corn syrup, more of it escapes absorption.

Unabsorbed fructose:

• draws water into the bowel, causing loose stools
• is fermented by colon bacteria, producing hydrogen, methane and carbon dioxide, which cause bloating, gas and pain

Many healthy people cannot fully absorb a large dose of fructose. Symptoms appear when the gut is also sensitive, as in IBS.

Fructose malabsorption vs hereditary fructose intolerance

Never perform a fructose breath test or fructose challenge if hereditary fructose intolerance is possible.

Symptoms

Symptoms usually start 30 minutes to a few hours after eating:

• bloating and abdominal distension
• excess gas
• cramping abdominal pain
• diarrhea, or sometimes constipation
• nausea
• rumbling stomach

High-fructose foods

Better-tolerated fruits often include bananas (firm), berries, citrus, kiwifruit, grapes and pineapple in modest portions.

Diagnosis

• Hydrogen breath test: you drink a fructose solution and breath samples are collected over 2 to 3 hours. A rise in hydrogen or methane suggests malabsorption. The test has limitations: many healthy people test positive, so the result must match your symptoms.
• Dietary trial: a supervised low-fructose or low-FODMAP diet for 2 to 6 weeks, with reintroduction, is often the most useful test.
• Ruling out other causes: blood tests for celiac disease, and assessment for lactose intolerance, SIBO and inflammatory bowel disease when symptoms suggest them.

Treatment

Low-fructose diet

1. Elimination: reduce foods with excess fructose and sorbitol for 2 to 6 weeks.
2. Reintroduction: gradually test foods to find your personal limit.
3. Long term: eat a varied diet up to your tolerance level. Most people can still eat some fruit.

Tips:

• spread fruit through the day in small portions rather than large servings
• eat fruit with a meal
• choose fruits lower in excess fructose
• read labels for honey, agave, high-fructose corn syrup and sorbitol

Low-FODMAP diet

Because fructose is one of the FODMAPs (fermentable carbohydrates), people with IBS often benefit from a broader low-FODMAP diet under a dietitian. See FODMAP intolerance.

Other measures

• glucose taken with fructose may improve absorption in some people
• xylose isomerase enzyme supplements have limited evidence
• managing stress and other IBS treatments help gut sensitivity

Avoid unnecessary long-term restriction, which can reduce fiber, vitamins and healthy gut bacteria.

Frequently asked questions

What is fructose malabsorption?

It is a condition in which the small intestine cannot absorb all the fructose eaten. The unabsorbed sugar is fermented in the colon, causing bloating, gas, cramps and diarrhea. It is common and harmless but can be uncomfortable.

What foods should I avoid with fructose malabsorption?

Limit foods with excess fructose: apples, pears, mango, watermelon, dried fruit, fruit juice, honey, agave and high-fructose corn syrup, plus foods with sorbitol. Most people can still enjoy berries, citrus, grapes and kiwifruit in moderate portions.

Is fructose malabsorption the same as fructose intolerance?

The terms are often used interchangeably for the common gut condition. Hereditary fructose intolerance is a different, rare genetic disorder of the liver that causes serious illness in babies and requires strict lifelong fructose avoidance.

How is fructose malabsorption diagnosed?

Doctors use a hydrogen breath test after drinking fructose, combined with your symptoms and response to a low-fructose diet. Other causes such as celiac disease and lactose intolerance are usually ruled out.