Fructans & the Low FODMAP Diet
Understanding what fructans are and how they fit with the low FODMAP diet can be tricky. Fructans like to lurk in a variety of foods, from fruit and veggies right through to cereal grains. They are also added to processed foods. This article is going to explain what they are and how to avoid them.
What are fructans and why are they a problem?
Fructans are oligosaccharides and polysaccharides that store carbohydrates in a variety of vegetables, for example, onions, garlic and artichokes, fruits such as bananas, and in cereals (1 2 3). Unripe common bananas contain low levels of fructans and are safe to eat, however as the bananas ripen the fructan levels increase to a high FODMAP level. In the FODMAP acronym fructans belong under the ‘O’ for oligosaccharides. Humans lack the enzyme needed to break down the fructose molecule chains that fructans are made of, which means they end up being malabsorbed in our small intestines (1 2). The fructans are then fermented by the gut bacteria, which can cause gas, bloating, pain, reflux, and altered bowel movements (2 3 4).
There are two types of fructans:
- Fructans with shorter chain lengths (2-9 units) are called fructo-oligosaccharides (Oligos-FOS for short)
- Fructans with longer chain lengths (10 units or greater) are called inulin. Inulin has already been discussed in depth in a previous article – you can read more about inulin here.
For the purpose of this article, there will be no differentiation between the types of fructans. Additionally, the different types of fructans are not labeled separately in the Monash University Low FODMAP app (3).
Fructans consist of soluble fibre (4). Adding fructans to processed food is a growing trend in the food manufacturing industry. This is because fructans (especially inulin) are considered a functional ingredient that can increase fibre content of processed food (4). The fermentable fibre is meant to help the growth of ‘friendly’ gut bacteria because they act like prebiotics (1 4), which is great for normal people but not so great for people who can’t tolerate FODMAPs! This means you should check the labels of processed foods and supplements for inulin, added fibre, and other fructans.
Where are fructans found?
Plants use fructans as storage carbohydrates. This means fructans can be found in a wide range of fruits, vegetables and cereals (1). Most types of beans/pulses/legumes and some nuts are also high in fructan containing oligosaccharides (3). One of our major sources of fructans is wheat, which means cutting out wheat can dramatically decrease our fructan intake (1 4). Below is a table of high FODMAP foods that contain fructans. This table is by no means intended to provide a full list of fructan-containing foods, but to show how many different foods contain fructans. For a more comprehensive list of fructan-containing foods and their FODMAP levels, please refer to the Monash University phone app or low FODMAP booklet.
High FODMAP Foods Containing Fructans (non-exhaustive list)
|Nectarine||Globe artichoke||Pumpernickel bread|
|Plum||Beetroot (>2 slices)||Wheat (dependent on serving size)|
|Pomegranate (>38g)||Savoy cabbage (>1/2 cup)||Barley|
|Watermelon||Garlic||Spelt (dependent on serving size)|
|Some types of dried fruit||Leek (bulb)|
|Common banana (ripe)||Mange tout (> 5 pods)|
|Onion (white, shallots, Spanish)|
|Spring onion bulb|
|Snow peas (> 5 pods)|
Do different foods have different fructan levels?
Different foods can contain different levels of fructans. It is also important to note that cooking, manufacturing or refining processes, and the fermentation of foods can change their FODMAP rating and fructan levels. For example, spelt sourdough bread is lower in FODMAP levels as the yeasts use the fructans during the fermentation process (5). Another example of changes in fructan levels is the drying of fruit. The drying process concentrates the sugar present in the fruit and can increase the fructan levels, even if these fructan levels weren’t detectable in the fresh fruit (5). The processing of cereal grains can also change the fructans levels in the end-products. The tables below indicate how fructan levels can change between foods.
Table One: High FODMAP Vegetables Containing Fructans
|Vegetable|| Grams of Fructans Per Average Serve*
(serve size in brackets)
|Grams of Fructans per 100g|
|White onion||0.28 (16g)||1.8|
|Spanish onion||0.30 (16g)||1.8|
|Leek whole||0.43 (83g)||0.5|
|Spring onion bulb||1.01 (16g)||6.3|
|Jerusalem artichoke||6.1 (50g)||12.2|
(Source: Muir et al., 2009)
Table Two: Cereals Containing Fructans
|Cereal||Grams of Fructans per 100g|
|Unprocessed Wheat||1.3 – 1.9|
(Source: Verspreet et al., 2015)
Reintroduction of Fructans
Section Updated on 21/04/2016
After the elimination phase of the diet, fructans can be re-challenged and reintroduced. Fructan levels can vary greatly between different fruits, vegetables, and cereal grains. This means you need to test one to two foods in each of the different fructan groups to find your tolerance levels (8). FODMAP reintroduction specialist, Lee Martin (RD), recommends that you re-challenge each fructan group separately:
|Number of Re-challenges||Fructan Group||Examples|
|Choose Two||Fructan containing vegetables||Garlic, leek bulb, onion (red or white), spring onion bulb|
|Choose One||Fructan containing fruit||Dried dates, dried pineapple, raisins, grapefruit, persimmon|
|Choose Two||Fructan containing bread, cereals & grains||Barley flakes, rice krispies, spelt flakes, white wheat bread, cous cous|
(Table Information Sourced from: Martin, 2015)
For more information, you can find my overview of the reintroduction phase here. Otherwise for a complete guide on reintroducing FODMAPs, check out Lee Martin’s Complete Guide to Re-challenging and Reintroducing FODMAPs.
Testing different fructan containing foods means you are more likely to find a fructan level you can tolerate. Hopefully you will be able to add some fructan containing foods back into your diet depending on your tolerance levels.
Until you figure out your tolerance levels to fructans you need to avoid high fructan foods in the elimination phase of the diet. Also remember to check all processed foods for added fructans from high FODMAP food sources like inulin and chicory root. If you are lucky, you might be able to add some fructans back into your diet during the reintroduction phase.
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