What are fructans?

August 16, 0209

A fructan is a polymer (essentially a large molecule) of fructose molecules which store carbohydrates. They can have either a short and long chain length are known as fructoligosaccharides (FOS) and inulin respectively. Fructans (along with galactans) account for the ‘O’ in the FODMAP acronym.

What foods contain fructans?

A wide range of foods including artichokes, asparagus, leek, garlic, onion, wheat and ripe bananas. Scroll down for more extensive list.

Onion & garlic contain fructans

Inulin (the long chain fructan), can be added to processed foods as a‘ functional ingredient’.

The addition of inulin increases the fibre content of the food product and acts as a prebiotic.

Cooking, drying, processing, sour-doughing, pickling, activating and sprouting foods (that already contain fructans) can increase or decrease that foods’ fructan content. Some examples:

  • Dried fruit (increased levels)
  • Rice cakes, corn cakes, cornflakes (increased)
  • Sourdough bread (decreased)
  • Pickled onions (decreased)
  • Activated cashews (decreased)
Processing, cooking and preparing foods can increase OR decrease the foods’ fructan content

Can my body breakdown fructans?

We don’t have the enzymes to break down fructans in our small intestine. This results in:

  • malabsorption (a condition that prevents absorption of nutrients) AND
  • fermentation by gut bacteria in our colon

Someone who has lactose intolerance can take lactase enzyme tablets to help break down any lactose that they have eaten.

It’s a different story if you need help breaking down fructans. There is no current product available on the market to do this job.

microrganisms such as bacteria ferment fructans that reach the large bowel.
Fermentation is the process where a substance breaks down into a simpler substance. Microorganisms, like bacteria, play a role in fermentation.

Can I eat too many?

Eating an excessive amount of fructans can cause an increase in flatulence / gas and mild bloating in many of us.

However, for people with functional gut disorders (such as irritable bowel syndrome), even eating small amounts of fructans can cause significant gut issues.

This may include abdominal bloating, distension, pain, reflux, excessive wind and altered bowel movements.

Aren’t they just the same as gluten?

Short answer. No. Wheat, barley, rye and oats are all sources of fructans. They also contain gluten.

All too often gluten gets mistakenly identified as the trigger if gut symptoms are experienced when these foods are consumed.*

Fructans are NOT the same as gluten.

Do I need fructans in my diet?

As described earlier fructans are prebiotics. Prebiotics are classified as fibres that pass through the gastrointestinal tract undigested and stimulate the growth and/or activity of healthy gut bacteria.

Malabsorption of fructans is a pre-programmed bodily function vital to the health of our gut (e.g. producing butyrate). With this in mind, there can be several downsides to a diet restricted in fructans.*

If fructans are restricted in the diet they should ALWAYS be rechallenged once symptoms settle. There may be unnecessary dietary restrictions otherwise.

The rechallenge process is recommended to be conducted in partnership with your dietitian to ensure optimal liberalisation. .

*keep an eye out for future articles where these ideas will be expanded upon.

Departing thoughts

Fructans are fibres that are poorly digested and malabsorbed which can lead to gastrointestinal disturbance in sensitive people.

They are contained in a wide variety of foods and should only be restricted above levels that trigger gastrointestinal symptoms.

Always consult your dietitian before undertaking a fructan-restricted diet.

High Fructan fruits

grapefruit (>100g)
nectarine
persimmon
pomegranate (>55g)
white peach
plum
watermelon
dried fruit (dried apricots, dried pineapple, dates, dried fig, dried mango, dried pawpaw, prunes, sultanas)
common banana (ripe)
blueberries (>1/2 cup)

High fructan vegetables

chicory root
globe artichoke
Jerusalem artichoke
fresh beetroot (>30g)
asparagus
Brussel sprouts (>3 sprouts)
Savoy cabbage (>3/4 cup)
fennel (>1/4 bulb)
garlic
leek bulb
onion, shallots, spring onions
snow peas (<7 pods)
green peas (>1/4 cup)
zucchini (>1/2 cup)

Asparagus, savoy cabbage and brussel sprouts contain fructans

High fructan cereals

wheat, barley, rye, oats (>1/2 cup)
spelt
couscous
freekeh
burghul

High fructan nuts/legumes

cashews (>10 nuts)
black beans / baked beans (>1/2 cup)
red kidney beans, pinto beans, split peas
lentil burgers, vegetarian mince
silken tofu (>1/2 cup)

*Please refer to the Monash University low FODMAP app or low FODMAP booklet for a complete list of fructan-containing foods

We can help you work out your tolerance to fructans.

Pic credits:
Bubbling liquid Photo by Frank Luca on Unsplash
Garlic & onion Photo by Ankit Manoharan on Unsplash
Arrow Photo by Hayes Potter on Unsplash
No Photo by Gemma Evans on Unsplash
Pomegranate Photo by Laura on Unsplash
Cabbage, asparagus on a pan Photo by Toa Heftiba on Unsplash

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