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A Beginner’s Guide to FODMAPs

A Beginner's Guide to FODMAPs. Fodmap diet, Naturopath Kirily Thomas, low fodmap

What are FODMAPs? Why am I suddenly reacting to FODMAPS? Should I go on a low FODMAP diet? These are three questions that come up regularly in my clinical practice. I have lots of patients also come to see me that are already on a long-term low FODMAP diet, as it made them feel better, or they have tried one in the past without much success, or it was not followed strictly, or they found it too confusing, overwhelming, and/or difficult to continue. So, today I have a beginner’s guide to FODMAPs for you to help you understand it better!

What are FODMAPs?

F O D M A P = Fermentable, Oligosaccharides, Disaccharides, Monosaccharides, And Polyols

FODMAPs are short-chain carbohydrates (sugars) that occur naturally in many of our foods – the amount people can absorb varies. They may be poorly absorbed in the small intestine in some people, meaning they’re available for fermentation by our gut flora in the large intestine/colon. This may cause uncomfortable symptoms in susceptible people, such as abdominal pain, bloating, distension, cramping, excessive gas, and changes in bowel habits, especially those with irritable bowel syndrome (IBS) and other functional gastrointestinal disorders (FGID) like functional abdominal pain and dyspepsia (1).

When someone has small intestinal bacterial overgrowth (SIBO), fermentation of these sugars can also occur in the small intestine by displaced bacteria, which may contribute to some of the adverse upper and lower gut symptoms being experienced such as nausea, bloating and belching.

What carbohydrates/sugars belong to each FODMAP section?


  • Short-chain carbohydrates (sugars) are improperly absorbed and feed gut flora in the colon > fermentation > gas > IBS and/or SIBO symptoms (in susceptible people).


  • Fructooligosaccharides (FOS/fructans) – chain sugar formed by fructose with glucose at the end e.g., wheat, onions, garlic, leeks, globe artichoke, jerusalem artichoke, yacon, asparagus, inulin.
  • Galactooligosaccharides (GOS/raffinose and stachyose) – chains of galactose that end with fructose and glucose e.g., legumes, chickpeas, cabbage, brussels sprouts.


  • Lactose – naturally occurring sugar found in milk and milk products e.g., milk, ice-cream, yoghurt.


  • Fructose – naturally occurring sugar that’s found in all fruits and many other foods (e.g., honey, apples, mango, pears, agave syrup) and is also often added to highly processed fast foods as a sweetener (more so in the USA).


  • Naturally occurring sorbitol and mannitol can be found in some fruit and veggies e.g., stone fruit, mushrooms, cauliflower, snow peas, blackberries.
  • Sorbitol (420), lactitol (966), xylitol (967), maltitol (965), mannitol (421), isomalt (953) and erythritol (968) are sugar replacements often found in “diet”, sugar-free, keto and low-carb products.

The list above provides you with an example of a small number of foods that contain FODMAPs. If you are after a comprehensive guide to the level of FODMAPs contained in various foods, I highly recommend that you download and use the Monash FODMAP App, which is an excellent resource that I recommend to all my patients if a low-FODMAP diet needs to be implemented.

Why am I reacting to FODMAPs?

It is very important to note that although FODMAPs can cause some very unpleasant gut symptoms in those with IBS, FGID, and SIBO, and removing them from your diet may certainly bring relief, FODMAPs themselves are usually not the underlying cause of your gut problems, instead, they may be additional sign/symptom that something has changed and is not right.

It is possible that your gut may have become more reactive/ hypersensitive to these fermentable compounds because of an underlying functional gut issue, or a condition like SIBO. Post food poisoning, nasty gastro or traveller’s diarrhoea is also a very common time for this type of reactivity to appear, usually because it triggers a condition known as post-infective IBS (1-5) and may have also disrupted the balance of your gut microbiota (this imbalance will also contribute to your unhappy gut).

These types of conditions often make the gut more sensitive, and the nervous system response in the gut over reactive (aka visceral hypersensitivity), to FODMAPs. This may cause the improper absorption of FODMAPs in the small intestine, with the gut then reacting adversely to the fermentation of these compounds in the large intestine (or small intestine with SIBO). To keep it simple, this leads to an increase in intestinal gas, abdominal distension, abdominal pain, and changes in bowel habits. The difference in gut response between someone with IBS and someone without IBS has been documented in various clinical trials where control subjects without IBS/FGID were found to have the same amount of fermentation and gas being produced in the gut as those with IBS/FGID, but they did not experience the same reactivity and adverse symptoms such as pain, bloating and flatulence as those with IBS (1-3).

Please note: cases of specific food intolerances (that may fall within the FODMAP group, like primary fructose intolerance), food allergy and anaphylaxis, inflammatory bowel disease (IBD), or other autoimmune diseases like coeliac disease (intestinal damage caused by exposure to gluten) can also be major contributors to gut symptoms, but they are separate to FODMAP intolerance, and may require different support. Although, they can also occur alongside one another, just to make things more complicated!

Should I go on a low-FODMAP diet if I have gut issues?

Whilst a low-FODMAP diet can certainly help to reduce adverse gut symptoms in many people with IBS, FGID and SIBO, it is best to undertake this step after checking in with your medical/healthcare practitioners to discuss if this is the best option for you given your history and current symptom picture. It’s normally suggested by your GP or specialist as an option to trial once any standard medical testing has come back as unremarkable (in medical speak), meaning you are clear of any significant diagnosable gastrointestinal illness or disease. As coeliac disease (autoimmune response to gluten) and other gastrointestinal diseases such as inflammatory bowel disease (IBD) can sometimes share some similar symptoms with conditions like IBS (which is less serious medically speaking, albeit unpleasant), it is important that conditions such as those are ruled out before any dietary change is commenced, as significant dietary changes, like cutting out gluten, can interfere with the diagnostic process.

Once things have been ruled out, or conditions have been diagnosed medically, via your GP or specialist, if appropriate, I do often suggest a temporary low-FODMAP diet to my own patients. This is usually if I think it will bring them welcome symptom relief whilst we are doing any necessary gut work, which is typically started after the completion of any additional testing that I may need to recommend (e.g., breath testing for possible SIBO or gut microbiome mapping/analysis) to work out exactly what is going on in the background gut-wise.

Contrary to what some people believe, the low-FODMAP diet is not meant to be a forever diet and should only be followed for a few months (depending on what is going on gut-wise, sometimes it may be longer in SIBO), with a plan for discussed for reintroduction and challenge. People often struggle with FODMAPs if they don’t have enough support with its implementation, or stay on it for too long (i.e., years) if they stop seeing their practitioner before the process is complete, and they don’t have a good understanding of why FODMAP reintroduction is important. Thus, it is very important to work with a practitioner semi-regularly during the time you are on a low-FODMAP diet, so you have professional advice and guidance along the way.

For the best chance of success, you may need to implement other supports/ interventions (under practitioner guidance) to help reduce the sensitivity and over reactivity of your gut, resolve other conditions like SIBO, and ensure that your gut microbiota is in better balance. This may help to improve the chances of not only reducing your gut symptoms, but also successfully reintroducing FODMAP containing foods down the track. Note: there are usually a few foods that may always be an issue for you – ongoing lactose intolerance is a good example of this – but the list of what you can’t eat should be significantly smaller than when you first started, and your gut should be feeling in much better shape!

I hope this beginner’s guide to FODMAPs has answered some of your questions and given you a greater understanding of this condition. Please get in touch for an appointment if you would like to find out how your gut health is tracking and if FODMAPs might be an issue for you.


  1. Bertin L, Zanconato M, Crepaldi M, Marasco G, Cremon C, Barbara G, Barberio B, Zingone F, Savarino EV. The Role of the FODMAP Diet in IBS. Nutrients. 2024 Jan 26;16(3):370. doi: 10.3390/nu16030370. PMID: 38337655; PMCID: PMC10857121.
  2. Major G, Pritchard S, Murray K, Alappadan JP, Hoad CL, Marciani L, Gowland P, Spiller R. Colon Hypersensitivity to Distension, Rather Than Excessive Gas Production, Produces Carbohydrate-Related Symptoms in Individuals With Irritable Bowel Syndrome. Gastroenterology. 2017 Jan;152(1):124-133.e2. doi: 10.1053/j.gastro.2016.09.062. Epub 2016 Oct 14. PMID: 27746233.
  3. Murray K, Wilkinson-Smith V, Hoad C, Costigan C, Cox E, Lam C, Marciani L, Gowland P, Spiller RC. Differential effects of FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols) on small and large intestinal contents in healthy subjects shown by MRI. Am J Gastroenterol. 2014 Jan;109(1):110-9. doi: 10.1038/ajg.2013.386. Epub 2013 Nov 19. PMID: 24247211; PMCID: PMC3887576.
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  5. Chan J, van Best N, Ward M, Arcilla MS, van Hattem JM, Melles DC, de Jong MD, Schultsz C, van Genderen PJJ, Penders J. Post-infectious irritable bowel syndrome after intercontinental travel: a prospective multicentre study. J Travel Med. 2023 Oct 31;30(6):taad101. doi: 10.1093/jtm/taad101. PMID: 37522760; PMCID: PMC10628768.
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