Fructans and the Low-FODMAP Diet

11 August, 2020 , ,

If you suffer from irritable bowel syndrome (IBS), you must have already heard of the low-FODMAP* diet. This diet is divided into three phases. First of all there is the elimination phase during which one removes from their diet, for 2 to 6 weeks, the 6 families of carbohydrates (Fructans, Lactose, GOS, Fructose, Mannitol and Sorbitol) which can often be the cause of digestive discomfort. Then, when the symptoms have disappeared, comes the approximately 7 weeks reintroduction phase. The goal is to test your personal tolerance to the different families of FODMAPs. To do this, every week you reintroduce a food, per FODMAP family, to find out to which family your digestive system reacts to. Once the culprits are identified, comes the maintenance phase during which you exclude from your diet the families that are causing digestive symptoms only.

Today we will focus our attention on a family of FODMAPs in particular called “fructans”.

What are fructans?

Fructans are so-called “oligosaccharides” or sugar chains made up of several simple sugar molecules (monosaccharides), in this case fructose, combined with a glucose molecule.

There is not a single fructan but instead it is a family composed of a variable number of molecules, joined in many ways.

Fructans are grouped into two categories:

  • those consisting of shorter chains (2 to 9 units) called fructo-oligosaccharides
  • and those with longer chains (10 units or more) called inulin.

Why is it so difficult to digest fructans?

Humans do not produce the enzymes capable of breaking down the bonds between the sugars that make up fructans. This means that our intestines can’t absorb them and, therefore, the fructans enter the colon whole. There, the bacteria that are present ferment them which causes gas, bloating and constipation in people with IBS (Irritable Bowel Syndrome).

On the other hand, for people who do not have irritable bowel syndrome, fructans promote the growth of good bacteria in the colon.

Why are fructans so complex?

Not only can fructans take many forms, but a food can contain several different types. In addition, they are found in a wide variety of foods: grains (wheat, rye, barley…), garlic and onions, fruits (white peaches, blueberries …) and vegetables (beets, zucchini …), in varying amounts. Also, 1 cup of cooked wheat pasta (148 g) is rich in fructans, the same as a single clove of garlic (3 g).

This explains why it is necessary to do several re-introduction tests for the fructans family. At a minimum you will need to do one test for grains and at least one other for garlic and onions. You might also want to test fruits and vegetables. These tests will allow you to best define the foods you react to and in which quantity. You may tolerate the fructans of certain foods and not others.

Is it true that fructans are everywhere?

Indeed, in addition to certain grains, fruits and vegetables, and garlic and onions, fructans are also found in commercially processed products, especially in the form of inulin. To help you spot them I invite you to read this article.

Fructans and gluten, what is the difference?

Fructans are found in the same grains that contain gluten: wheat, barley, rye and spelt. As we have seen, fructans are carbohydrates, and gluten is a protein. So, you may think that you have an intolerance to gluten when it is in fact the fructans that bother you. Here is an interesting article if you want to learn more.

In addition, if you suffer from digestive problems, I advise you to consult with a specialized dietitian who will help you to reduce your symptoms and improve your quality of life.

*FODMAPs are fermentable carbohydrates that are partly responsible for causing symptoms in people with irritable bowel syndrome (IBS). For more info, read this article.


  • Monash University. Fructans and FODMAP reintroduction. June 2020.
  • Monash University. What are the oligos? March 2016
  • Fedewa, A., & Rao, S. S. (2014). Dietary fructose intolerance, fructan intolerance and FODMAPs. Current gastroenterology reports, 16(1), 370.
  • Skodje, G. I., Sarna, V. K., Minelle, I. H., Rolfsen, K. L., Muir, J., Gibson, P. R., … & Lundin, K. E. A. (2017). Fructan, and not gluten, as symptom trigger in self-reported non-celiac gluten sensitivity. Gastroenterology.
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Jennifer Morzier

Jennifer Morzier

Jennifer is a Registered Dietitian graduated from the University of Montreal in December 2018 and is a member of the Ordre professionnel des diététistes du Québec (OPDQ). She believes that the quality of our food choices has a direct impact on our health and energy level. Her goal? To help people improve the quality of what they put in their plates, for their better well-being and greater pleasure.

Jennifer Morzier

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