Invert Sugars, Fructan Chain Length and the Monash University Low FODMAP App


Morning all! About a month ago I said that I was going to email the Monash University researchers with a list of questions and I did, it just took a while to get all the responses, as I asked a few follow up questions and they are understandably very busy! Well, here are the answers.

Please note that the researcher has asked me to paraphrase some of her answers, as they are purely speculating on some things at this point, so she wasn’t happy with their thoughts on potential causes being published. I feel that it is a reasonable request, as there is so much confusion out there regarding FODMAPs that any “if’s and maybe’s” added into the mix would just make the situation worse.

My questions will be in italics, followed by the paraphrased answers in normal text:

Invert sugar

What exactly is invert sugar and why is it unsafe for a low FODMAP diet? Theoretically, invert sugar can be 1:1 fructose/glucose, yet many people still have issues with it. We have discussed on the FM VIC Facebook group how invert sugar can be made (either naturally, as in honey – which is still fructose > glucose as a separate issue, or chemically – heating sugar with an acid, such as in making jam or golden syrup) and we can’t figure out why people seem to be reacting to invert sugar when it’s listed as an ingredient on a packet but can tolerate jams and golden syrup etc. These are our thoughts; as you can see, we’ve come up with many hypotheses but do not have the expertise to narrow them down.

  • The process of separating fructose and glucose – to prevent crystallisation – means that fructose can no longer use the glucose co-transport method of absorption in the small intestine.
  • There is something involved in the process of intentionally making invert sugar that causes it to become problematic, rather than invert sugar simply being a by-product of heating sucrose in the presence of an acid.
  • The initial proportion of fructose to glucose in the substance turned into an invert sugar plays a role; i.e. it’s not always sucrose as a reactant.
  • Enzymatic vs heat/acid breakdown of sucrose to fructose and glucose plays a role.
  • The sheer amount of invert sugar that may be added to a packet food, compared to a teaspoon or two of jam or golden syrup on your toast, could be an issue. 
  • The separation of sucrose into fructose and glucose before the small intestine (i.e. in a saucepan or a factory), where it would otherwise be digested in situ by sucrase (or invertase?) means that the fructose and glucose aren’t close enough together in the lumen to make co-transport possible?

We do not have any data specifically looking at invert sugars, therefore we can also only speculate. As we know that excess fructose is problematic, perhaps the ratio of fructose and glucose is not always 1:1 in invert sugars. If glucose and fructose are consumed together – then we would expect that they would be able to be absorbed as a combined unit. However if these pathways are saturated – then the excess glucose will not assist (as all the pathways have been used up).

Are there any plans to test or study invert sugars? 

Not that I am currently aware of.

Does the chain length of a fructan/FOS molecule affect our body’s ability to tolerate it?

With regards to fructans and chain length, I’ve read an article abstract that hints that the chain length of oligosaccharides may play a role in our ability to tolerate them. In the FM VIC Facebook group, we have hypothesised that longer chain lengths are less problematic with regards to fermentation, as they take longer for the bacteria to digest and hence may pass through the colon before too much gas etc can be produced. Would it be wrong to hypothesise that spelt and rye are better tolerated than wheat amongst fructose malabsorbers because their fructans are longer? I have come across many people that can tolerate spelt and rye (even when not pre-fermented as in sourdough), compared to wheat – myself included.

There is no published data on the differences in chain lengths of fructans showing a real affect in IBS patients.I therefore cannot give you a confident answer either way. To date it is only speculation but that may change, as data in the future may indeed explain it. Note that the total FODMAP content is important to consider. Rye bread has significantly higher fructan content compared to wheat breads. Therefore Spelt sourdough is the most suitable option. We also don’t know if the fructan chain length is affected by processing, seasonal changes etc. Therefore one rye bread may be different to the next.

With regards to the fructans in rye, do you have any idea why, given the greater amount of fructans present, it seems to be better tolerated than wheat? I ask this because a few rye recipes have been passed around the FM support group on Facebook, some people say they can tolerate a slice or two of 100% rye bread every few days but most people cannot tolerate wheat, so we were wondering why this was, given rye should fill up the “FODMAP bucket” sooner than wheat based on fructan concentration alone.

As this has not been extensively studied, we cannot say for sure. There are many patients who can tolerate small quantities of wheat – so we would encourage everyone to continue to challenge with wheat to test tolerance.

A general question on the FODMAP App

When is the next app update scheduled and will it contain information on coffee/tea/chocolate (the updates from late last year) and individual flours?

We are working on the next update of the app. However, due to having to change over to iOS7 it has been delayed. We hope the next update will be released in a few months time. For now, the best way to get tea/coffee information is from our website

Thanks for that. Is there any chance of getting the FODMAP app on a smart phone platform other than Apple or Android? It’s a long shot but worth asking.

No, at this stage there is no plan to make the app available on platforms other than Apple or android. The iOS7 apple upgrade has resulted in a delay in any new app updates being released.

I would like to thank the researchers at Monash University on behalf of myself and everyone in the FODMAP community, both for taking the time out of their busy days to answer the questions that we pose to them, as well as for their hard work, which has been life changing for many of us. Cheers guys, much appreciated.

Also, if you would like me to paraphrase my answers any further, please let me know and I will happily do so.



2 thoughts on “Invert Sugars, Fructan Chain Length and the Monash University Low FODMAP App

    • No worries. I was a bit disappointed that I got “we don’t know yet” as answers but it’s still really early days in terms of researching FODMAPs, so this is understandable. They probably want to test as many foods as possible before they focus on the more intricate details of individual FODMAPs. Hopefully we know more about them soon!

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