Fructose intolerance test

Appointment required

Fructose intolerance test using a breath test with a fructose load. It makes it possible to investigate whether fructose is absorbed properly and whether its fermentation is linked to bloating, wind, abdominal pain or diarrhoea.

No prescription needed, appointment required

Results in 3-5 working days after the test

Breath sample. Includes: Fructose breath test. See what it measures

What it is for

It is used to investigate possible fructose malabsorption when symptoms appear after fruit, juices, soft drinks, honey or products with added fructose. The amount eaten and the combination with other sugars have a strong influence, which is why the link with foods can seem inconsistent.

The test gives an objective measure of fermentation, but clinical intolerance is established by relating the curve to the symptoms. It is not designed to justify a fruit-free diet in general.

When it is recommended

Bloating, wind, pain or diarrhoea after eating fruit or drinking juices, honey or soft drinks
Digestive symptoms that seem to depend on the amount of fructose consumed
Symptoms that persist after other, more likely causes have been investigated
Before starting a long-term fructose restriction without a clear diagnosis

Clinical comment

Fructose malabsorption is not the same as hereditary fructose intolerance. The latter is a genetic metabolic disease, rare and potentially serious, which is diagnosed by a different route. The breath test does not investigate it.

Small intestinal bacterial overgrowth can produce a false positive, because fructose ferments before it reaches the part of the bowel where it should be absorbed. If bloating appears with many different foods, or diarrhoea and constipation alternate, it is worth considering that possibility before attributing everything to fructose.

Nor does a positive result show how much fructose each person tolerates. Its practical use is to adapt intake without cutting out whole food groups, and to check whether symptoms improve consistently.

Dr. Antonio Mas

What is tested

• Fructose breath test (exhaled hydrogen): After taking a standardised amount of fructose, it measures hydrogen in exhaled breath at intervals. If part of the fructose is not absorbed in the small intestine, it reaches the colon and ferments.

Fructose breath test (exhaled hydrogen)

How to prepare

An appointment and 12 hours of fasting are required, and you must follow the preparation diet set by the centre on the previous day. Do not take antibiotics during the 4 preceding weeks, or laxatives or prokinetics during the preceding week.

The test lasts between 2 and 3 hours and you must stay at the partner centre. Do not smoke or exercise during the hours before or during the test.

You can add

Without another needle. It is offered when you order, so you do not have to decide now.

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Related blood tests

We have other profiles in Digestive with more or fewer tests:

The most comprehensive is not always the most useful. Each profile page explains when it makes sense and when it does not.

What it is based on

Rezaie A, Buresi M, Lembo A, et al. · American Journal of Gastroenterology 112(5):775-784
Hydrogen and Methane-Based Breath Testing in Gastrointestinal Disorders: The North American Consensus
Sets the fructose load for the breath test at 25 g and warns that bacterial overgrowth can give a positive result that is not fructose malabsorption: in patients with a positive lactulose test, positive fructose tests fell from 62 % to 3 % after one week of antibiotics.

Protocol designed by Dr. Antonio Mas, specialist in Endocrinology and Nutrition, Spanish medical licence no. 080846289, and reviewed in September 2026.

This blood test is a standardised protocol and does not replace a medical consultation. If you have symptoms, a known condition or a complex clinical situation, speak to your doctor.