What Is Xylose Isomerase? The Enzyme That Converts Fructose and Glucose

Xylose isomerase is an enzyme that converts the sugars glucose and fructose into each other (1). In our supplements, it supports the digestion of fructose by converting it into glucose in the small intestine.* In your body, xylose isomerase has no natural digestive role, because the enzyme comes from microorganisms (1).

This page is part of our guide to digestive enzymes. Below you will learn what xylose isomerase is, what it does with fructose, and where you find it in our products.

written and reviewed by Anouk Martini (registered dietician)

In short

Xylose isomerase is an enzyme that converts glucose and fructose into each other (1).
The enzyme is common in bacteria. Your body does not make it for digestion (1).
In our supplements, it supports the digestion of fructose by converting it into glucose in the small intestine.*
Xylose isomerase is in our products Fructase and Fodmix.

What is xylose isomerase?

An enzyme is a protein that speeds up a chemical reaction. Xylose isomerase, also called glucose isomerase, catalyzes the reversible conversion of glucose to fructose and of xylose to xylulose (1). The enzyme is widely found in bacteria (1).

The reaction runs in both directions. The food industry uses xylose isomerase to turn glucose into fructose for high-fructose corn syrup (1). In our supplements, the enzyme is used to convert fructose into glucose.*

What does xylose isomerase do in the body?

Your body does not make xylose isomerase for digestion. This is how it fits into the digestion of sugars:

Fructose arrives with your food. Fructose, or fruit sugar, is found in fruit, fruit juice, vegetables, sweets, and honey. Table sugar contains it too, bound to glucose.
Your small intestine absorbs simple sugars. Carbohydrates break down into simple sugars, and the small intestine absorbs them into your bloodstream (2).
A supplement adds the enzyme. Xylose isomerase from a supplement supports the digestion of fructose by converting it into glucose in the small intestine.*

Which foods contain fructose?

Fructose is primarily found in:

Fruit and fruit juice
Honey
Some vegetables
Sweets and sugary drinks
Foods with added sugar

When might xylose isomerase help?

Some people take a xylose isomerase supplement with meals that contain a lot of fructose, such as fruit, fruit juice, or sweets. Age, diet, lifestyle, and stress can all affect how well digestion works, and so do the size and type of a meal. A supplement does not replace a balanced diet.

Not sure whether a supplement fits you? Talk to a doctor or dietitian.

Where is xylose isomerase in our products?

Xylose isomerase is in two Intoleran products:

Fructase contains 7500 units per capsule of the digestive enzyme xylose isomerase, which supports the digestion of fructose by converting it into glucose in the small intestine.* Fructose (fruit sugar) is primarily found in fruits, fruit juice, vegetables, sweets, and honey. Fructase is suitable for vegetarians and vegans and free of soy and gluten.
Fodmix contains xylose isomerase (7500 u), alpha galactosidase (1200 u), lactase (10,000 FCC), and invertase (500 u). Fodmix helps reduce occasional gas, bloating, and discomfort, allowing you to enjoy meals without restrictive diets.*

Looking for the supplement itself? Read more about the xylose isomerase supplement.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Not sure which enzyme you need?

Digestive enzymes each have their own job. Answer a few questions in our supplement advisor and see which products fit your situation. You can also ask our dietitians a question.

When should you talk to a doctor or dietitian?

Do your symptoms persist, are you losing weight without trying, or are you cutting out more and more foods? Talk to your doctor or a dietitian. A supplement does not replace medical advice.

Fructose is one of the sugars in table sugar. Invertase splits sucrose into glucose and fructose, and alpha-galactosidase works on galactans. See all of our digestive enzymes.

Sources

Bhosale SH, Rao MB, Deshpande VV. Molecular and industrial aspects of glucose isomerase. Microbiol Rev. 1996;60(2):280-300. doi:10.1128/mr.60.2.280-300.1996
National Institute of Diabetes and Digestive and Kidney Diseases. Your digestive system & how it works [Internet]. Bethesda (MD): National Institute of Diabetes and Digestive and Kidney Diseases; last reviewed 2017 Dec. Available from: https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works