Frequently Asked Questions on Reintroducing

Since the book was published we have had some really good questions sent through. Here is a pick of the best ones with our answers, please do continue to get in touch this page will be continually updated.

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1. When reintroducing a food e.g. avocado, do you just eat the avocado by itself or do you eat it in combination with a low FODMAP meal?

When re-challenging it is best to have the high FODMAP foods in combination with low FODMAP foods. Practically this might not work for all foods but in general try not to isolate the high FODMAP food. The reason for this is firstly because this would be more like how you would normally eat, making the re-challenges realistic. Secondly it is thought high FODMAP foods eaten in isolation, especially on an empty stomach, may be more of a trigger of symptoms. As you want the re-challenges to be as accurate as possible it is best to eliminate the chance that eating a high FODMAP food in isolation triggers symptoms when normally you would not do this. In the book there are tables detailing all the  foods you need to try when re-challenging individual FODMAPs like this. The tables also include the portion sizes you need to test and how to increase these during the reintroduction. 

2. Should you do three consecutive days or alternative days when reintroducing?

The simple answer is you can do either and it is best to choose the one that suits you best. This may either be due to lifestyle or how you know your symptoms affect you. For example if you commonly get symptoms a day after eating a high FODMAP food then using the alternative day approach may be better. The book explains both methods of re-challenging, using a systematic protocol to follow, so you can make the best choice for yourself. Have a read of this article here which gives some ‘Top tips to get you started when re-challenging FODMAPs’.

3. If I take a probiotic should this before reintroducing FODMAPs or after?

Definitely try to complete the reintroduction phase first before trialling any probiotics or prebiotics. Otherwise it may affect your re-challenging results and you may not know which FODMAPs you can tolerate. When trialling different treatments for your IBS it is best to stick to one at a time. Therefore complete the reintroduction phase of the low FODMAP diet and if you are still getting symptoms then you can consider trialling a probiotic or prebiotic.
The evidence for probiotics and prebiotics improving IBS symptoms are varied with some positive effects on symptoms while other reports showing they are no more effective than a placebo. A recent systematic review on systematic reviews (found here) looking at the use of probiotics in IBS came to no clear conclusions on their use for relieving symptoms. In other words they might work or they may not, but they will cause no detrimental effect.

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4. I have tried reintroducing before and I reacted to most FODMAPs does this mean I should restrict these forever?

While it is certainly right in saying that you need to restrict foods that trigger symptoms if this is a long list then it is worth attempting reintroducing again as tolerance levels to FODMAPs change over time as does IBS. The reintroduction phase is by far the hardest part of the low FODMAP diet and there are no clear ‘black and white’ answers so it can become complicated. This is why is is best completed under the guidance of an experienced dietitian. It is also important to make sure you follow a correct re-challenging protocol as there are plenty of incorrect reintroduction protocols floating around the internet which I have written about previously here. The book provides the most widely used and recommended protocol for reintroducing along with ’10 tips for re-challenging’ to ensure you give yourself the best chance of success.

5. Is it correct that you have to complete three washout days after one FODMAP re-challenge even if you do not get any symptoms?

Yes this is correct. It is best to leave 3 days after finishing a re-challenge before starting a new one. The reason for this is to reduce the chance of any ‘carry over’ effects. For example if you have just tested a large portion of fructans without symptoms and the next day start a re-challenge of sorbitol and get symptoms it might have been the combination of fructans and sorbitol triggering symptoms rather than the sorbitol on its own. This may make it longer to complete the re-challenges but it should keep your results clear. The protocol in the book for re-challenging yourself with FODMAPs includes this important washout period. The article linked here will give you more information on this and other ‘Common mistakes when reintroducing FODMAPs’.

6. Have I made my gut far more sensitive by being on the low FODMAP diet for so long? I seem to get more severe symptoms when eating high FODMAP foods, even in small amounts?

I have seen in clinical practice and heard of people reporting similar things about increased sensitivity to high FODMAP foods when they have followed the low FODMAP diet for a long time. There is no research on this aspect of the diet as yet and it is worth remembering that all the research has indicated you only need to follow a low FODMAP restriction diet until you get a reduction in symptoms. For most people this is between 2-3 weeks and recent guidelines (found here) on the low FODMAP diet suggest you should stop the diet if after 4 weeks on  a low FODMAP diet you have not seen a reduction in symptoms.

It is also unknown what detrimental effects a long term low FODMAP diet has. Potentially it could alter your gut microbiota in a negative way and cause further gastrointestinal symptoms in the long term. By avoiding high FODMAP foods you will also be avoiding different types of fibre, natural laxatives and prebiotics found in high FODMAP foods. All of these have potential health benefits. You should try and re-attempt the reintroduction phase of the diet so you can learn how to follow a modified low FODMAP diet for the long term. If you can you should see a dietitian who can help with the complexities that arise.

7. Testing one FODMAP at a time seems the most sensible approach vs testing several different FODMAPs in one day. However, it seems like this would take so long to get through each group?

At the moment there is no universally agreed approach to reintroducing FODMAPs. However there is a lot of misinformation about reintroducing FODMAPs on the internet which I have written about before.  The ‘Re-challenging and Reintroducing’ book discusses the two options most widely used and practised by the majority of dietitians worldwide. Usually the re-challenging process takes 10 weeks to complete and this will help people to understand what individual FODMAPs and what portion size of these FODMAPs they can tolerate. This then allows relaxation of the low FODMAP restriction diet and a reintroduction of FODMAPs back into the diet. To completely reintroduce FODMAPs and understand how the combination of FODMAPs triggers your symptoms is an ongoing process.

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8. Following the low FODMAP diet has improved my IBS, although I still get symptoms, but wish I could just eat what I wanted. It really gets me down.

A statement like this indicates that following a low FODMAP restriction diet is affecting your quality of life. There is an extremely important point to consider here. A treatment that works on improving symptoms initially but affects quality of life long term is not a complete treatment. If you feel your food restrictions are affecting your quality of life you should seek advice from a dietitian or other medical professional.

9. On the final day of testing the large portion size I’m not sure if I can manage to eat that large a portion size of food, should I still do the test?

You should not eat the large portion size if you would not do normally. You have to keep things realistic. Importantly do not forget the ’10 rules of reintroduction’ in the book. Rule 9 says ‘You do not need to re-challenge the large portion size if it is unrealistic or seems too large for your normal consumption’. In the FAQ section at the end of the book there is a question which says ‘Do I have to use the portion sizes recommended or can I try smaller amounts first?’ This will give you more information on adjusting your portion sizes to suit your individual needs. The book provides a guide for portion sizes but is not a substitute for individual advice so keep it realistic for yourself. If you are a 150kg man you would not eat the same as a 50kg woman so adjust the portion sizes appropriately buy either slightly increasing or decreasing the portion sizes. Reintroducing is a complex task but do not make it harder or more stressful than it needs to be. Have a read of this article which cover ‘5 common mistakes when reintroducing FODMAPs’.

10. Is it unhealthy to follow the low FODMAP restriction diet long term?

At the moment this is unknown and research on this topic will be hard to complete, however for some it is likely it will be. For some people following a restricted diet long term (no matter what the diet is) can lead to nutritional and mental health problems. As for following a long term low FODMAP restriction diet the concern is also around the change to gastrointestinal microbiota caused by restricting your intake of FODMAPs. As FODMAPs contain prebiotics which are known to have many gut and health benefits restricting these long term could cause more health problems in the future, including more gut issues. This is an avenue of research which those researching the low FODMAP diet are very interested in. For more information on the gut microbiota and its importance for long term gut health see here.

11. Is there a difference between reintroducing and re-challenging FODMAPs?

Re-challenging is the process you go through to test your tolerance levels to individual FODMAPs and will usually last about 10 weeks. Take a look at this article discussing some great tips to get started on the re-challenge phase. Reintroducing is when you bring high FODMAP foods back into the diet and combine different high FODMAP foods to work out you FODMAP threshold. This is an ongoing process and does not involve additional tests just monitoring of your symptoms.

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12. How long does it take to notice a reaction after re-challenging or reintroducing a FODMAP?

The time it takes to trigger symptoms will be different for everyone. Usually if you have a slow gut transit time, as often people with IBS-C might have, you tend to feel symptoms later than someone with a faster gut transit time. This is a generalisation however and different FODMAPs have different effects so it makes sense that you may react to one FODMAP quicker than others or not get symptoms at all. Dr Jaci Barrett from Monash University discusses the ‘timing of symptoms’ in her bog post and this concept was further expanded in an interesting article by Dr Nick Read (found here).

13. Can it be possible to tolerate fructan vegetables and fructan fruits, but not tolerate fructan grains or vice versa?

The concentrations of fructans in foods are quite varied and structurally have different chain lengths meaning some might cause more symptoms than others (although this hasn’t been fully studied). Wheat tends to contain lower concentrations of fructans but within wheat there may also be other fibres and proteins including gluten that can also cause problems but are not fully understood as yet. Remember to consider the portion sizes as well. For example if you eat a large baguette it might be that this is simply too large a portion size for you regardless of the FODMAPs. Symptoms are not always due to FODMAPs. See here for common mistakes made when reintroducing FODMAPs.

14. I am starting to worry about reintroducing foods. I feel better than I have for ages and I don’t want to change anything.

Your trepidation is understandable but there is no need to worry about the reintroduction phase. If you approach it systematically and sensibly you will complete it and have a much better understanding of what foods you can and cannot have in moderation. This helps so much more for long term self-management. Potentially cutting out food groups for the long term (by this I mean continued restriction of food high in FODMAPs) may lead to the development of nutritional inadequacies. If you cannot get dietetic support then the ‘Re-challenging & Reintroducing FODMAPs’ book will provide a simple guide to walk you through reintroducing and take the stress out of the process. The reintroduction phase is the most important part of the low FODMAP diet; have a read of this article explaining ‘The importance of reintroducing FODMAPs’.

15. If you react to a FODMAP do you cut this FODMAP and all foods it contains out of your diet completely?

If a FODMAP triggers symptoms it doesn’t necessarily mean you need to cut out all foods containing that FODMAP. It depends on your symptom reaction and the portion size or amount of FODMAP you tested. In addition your tolerance to FODMAPs can change over time so it is always worth re-challenging FODMAPs that initially triggered symptoms again in the future. Take a look at the case studies in he book to help you make more sense out of your FODMAP reintroduction results.

16. I re-challenged honey by eating one teaspoon from the jar and experienced symptoms but I tested negative for a fructose breath test, I thought I could eat fructose?

A negative test for fructose malabsorption does not mean you will not get symptoms when eating fructose, as some research studies have shown (see here for open access paper). Also eating honey straight from the jar is probably not the most realistic way to test fructose. Testing individual FODMAPs in isolation is more likely to trigger symptoms, it is better to have it with other low FODMAP foods. Have a read of this linked article here describing common mistakes on the low FODMAP diet. To be sure if fructose is a problem for you it would be best to test a small portion size of 1 teaspoon again, for example, on a suitable low FODMAP bread and monitor any reactions then test a medium portion size the next day. If appropriate you can further test a large portion size on the third day but only if you had none or only mild symptoms from testing the medium portion size and only if you would actually ever eat that amount normally. Finally if you do not usually eat honey in your diet there are other foods you can test for fructose all listed in the book.

17. Some sources say to do the low FODMAP restriction diet for 6-8 weeks but after five weeks the last three weeks have been symptom free is it too early to start reintroduction?

It is not too early to start after 5 weeks and you should definitely start the reintroduction phase now. The restriction phase of the low FODMAP diet only needs to be followed until you see a reduction in symptoms. Previously when there was less research on the low FODMAP diet it was suggested to do the diet for 8 weeks or even longer if symptoms had not resolved. As more research was completed it was found that an average of 2-3 weeks was enough to see if the low FODMAP diet was effective. In fact following it for longer may make it harder to complete the more important reintroduction phase. The whole point of the low FODMAP restriction diet is to reduce your symptoms, therefore once you have symptom resolution you should start reintroduction. In general following a low FODMAP diet for between 2-6 weeks is a good time line, however if you have followed the low FODMAP diet for 4 weeks and have not seen any symptom improvement then you should stop and consult your health professional. It is unlikely you will see any further benefit if after 4 weeks on the diet nothing has changed. See these recent guidelines (found here) based on a systematic review of the evidence of a low FODMAP diet for more information.

18. I have reintroduced the FODMAPs I can tolerate back into my diet after re-challenging but have now experienced some symptoms, why is this?

It is likely the overall load of FODMAPs from combining FODMAPs has pushed you over your FODMAP threshold. You have worked out your tolerance levels to individual FODMAPs but it will take time, practice and a few mistakes to discover the level of FODMAPs you can eat before you go over your threshold and experience symptoms. For example you might be able to tolerate a high FODMAP portion size of mannitol or fructan grains by themselves but together it could push you over your threshold limit. You might need to try smaller portion sizes or just enjoy the high FODMAP foods individually with other low FODMAP foods. Try this: when you are eating a combination of FODMAPs and you trigger symptoms with foods you know you are okay with in isolation try reducing the portion size of the combination and see if that still causes a reaction. Finally it may be a good idea to go back on a low FODMAP diet for a few days to settle your symptoms before attempting more reintroducing. More information on reintroducing FODMAPs can be found in section 2 of the book along with a list of tables identifying foods that contain more than one type of FODMAP.

19. I have completed my re-challenges and I have had very small reactions to only large portions and sometimes to medium. Now I want to reintroduce do I have to test every food that contains more than one FODMAP?

You do not need to test every food with more than one FODMAPs and the reintroducing of combined FODMAPs should not involve more testing – just eating :). What you should do now is stop the low FODMAP restriction diet and gradually reintroduce FODMAPs back into your diet. It sounds like you have a relatively high FODMAP threshold to individual FODMAPs so you will probably be able to eat a couple of high FODMAP foods together before triggering symptoms. In your case it will most likely be the overall load of FODMAPs that trigger symptoms rather than individual FODMAPs. This may be over the course of one day or a few days and this is what you need to concentrate on and be aware of now.

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20. What else I could use for testing fructans in vegetables? I don’t eat garlic in my normal diet and I eat very little onion and not much of the other foods as I do not like them.

The book provides a table of vegetables that contain fructans although if you do not usually eat the vegetables that only contain fructans then I would not worry about doing this test. When you start reintroducing and combining FODMAPs you will have more choice of vegetables to eat so be aware of what other FODMAPs these foods contain and how they affect your symptoms so you can monitor any reactions.

21. How long does a ‘FODMAP reaction’ take? If longer than 24 hours, how will I know which amount I reacted to?

People will ‘react’ to FODMAPs differently and it will depend on a number of factors including their gut transit time, visceral hypersensitivity, what the trigger FODMAP was and how easily it is absorbed in the body, plus stress and anxiety has an impact. This is why it is so important to follow a systematic re-challenging protocol to try and make the tests as accurate as possible. If you know from your own experience that your reactions tend to take a long time then you can do the alternative day protocol as described in the book so have a look at this section. Have a read of this article by Dr Nick Read from the IBS Network which explores this interesting topic.

22. Do I just need to test one re-challenge per FODMAP? For example f I test almonds for GOS and I find I can eat some (or all) portion sizes can I then eat any foods containing GOS at these tested portion sizes?

As mentioned in the book it is the FODMAP you are testing not the food so once you have gone through the different re-challenges it will give you an overall indication of the ones that trigger your symptoms and at what portion sizes. Remember all FODMAPs require at least one re-challenge while fructans require up to five. See this really useful article (linked here) for top tips on starting the re-challenge phase of the low FODMAP diet.

23. Whether I get a positive or negative result should I re-challenge twice just to be sure?

It is not worth retesting if you did not have any symptom reaction. If you feel that when you did a particular test it didn’t go well or you had other things on your mind that may have affected the test results then yes you can repeat it. I would not do this for every test unless you found that you react to every FODMAP which is usually an indication that other factors were causing your symptoms. I would suggest seeing a dietitian or suitable healthcare professional if this is the case.

24. I’m doing the reintroduction phase after several months of complete FODMAP elimination but when I re-challenged GOS using chickpeas I felt like I bloated instantly?

If you have avoided FODMAPs for a long time you may be more sensitive to their effects. In this case for reintroducing it may be worth using smaller portion size than generally recommended to test your tolerance levels. To use a practical example when re-challenging chickpeas eat 1 tablespoon for the first day challenge, preferably within a low FODMAP meal and assess your symptoms, in your particular case bloating is most predominant.  Gradually increase the portion size during the next two challenges and hopefully you will be able to eat larger serves without any problems on sequential days. Even though 1/4 cup of canned chick peas is considered low FODMAP for you this may still trigger symptoms so go slowly and you will still be able to attempt the re-challenging phase. Remember galactooligosaccharides (GOS) are digested by bacteria in your gut so some mild bloating may occur but this is normal and should not be a huge concern. Have a read of this useful article by the Monash research team. In addition if it is hard for you to be symptom free for 3 days between re-challenges then just ensure your symptoms are at a baseline level before commencing the next FODMAP challenge.

25. I am ready to start but I’m putting off reintroducing because if I do experience symptoms does this mean it’s goodbye to certain foods forever?

Just because you find a FODMAP triggers symptoms it doesn’t mean you avoid it for life, it depends on the portion size you can tolerate and the severity of your symptoms. If you have trepidation about the reintroduction phase make sure you get help from a dietitian to individualise the reintroduction for you. If you cannot get hold of a dietitian then please do check out my book which will walk you through the whole reintroduction phase. It will help take the stress out of reintroduction by providing a detailed and systematic approach to the FODMAP challenges using the most up to date and trusted methods.

26. Can your gut ever get ‘used’ to FODMAPs again?

Your tolerance to FODMAPs can change over time due to the nature of IBS being a functional issue and perhaps due to differences in gastrointestinal microbiota. Re-challenging FODMAPs at the correct quantities using a food challenge protocol is the best way to get ‘used’ to FODMAPs. Certainly if you follow this method you will be able to work out your tolerance levels to FODMAPs and continue to eat high FODMAP foods to tolerance. If you continue to avoid FODMAPs and do not reintroduce it may cause your gut to become more sensitive to the effects of FODMAPs making eating any foods containing FODMAPs harder.

27. I completed my re-challenges using onion to test fructans with no ill effects. Does that mean I am alright with fructans, or do I need to trial every food in that group?

When you are challenging foods it is the FODMAP you are testing your tolerance levels to not the foods. You should test two types of fructan containing vegetables to get a better understanding of how fructans in these sort of foods affect you. Frucatns in vegetables are found in different concentrations within these foods meaning you may react to a vegetable with a high concentration of FODMAPs e.g. onion, but not experience symptoms from a vegetable with a lower concentration of FODMAPs e.g. okra.

28. As the impact of FODMAPs is cumulative, how does one go on when there are a number of FODMAPs in one meal e.g. wheat pasta with a sauce containing onion and garlic?

Once you have completed all the necessary re-challenges you can then start to reintroduce FODMAPs and test your FODMAP threshold for combinations of FODMAPs.


This reintroducing phase is not done in tests like the re-challenges but is more trial and error as part of your normal diet. Like you mention the effects of FODMAPs are cumulative therefore the more FODMAPs you have the more likely you are to experience FODMAPs. Discovering your FODMAP tolerance level is an ongoing process and most people end up following a modified low FODMAP diet to prevent going over their FODMAP threshold level and triggering symptoms like the diagram shows.

29. If someone has a symptom reaction during the re-introduction phase, should they still implement a 3-day washout period or less?

The three days washout period has two main aims. Firstly it is to help reduce symptoms to a baseline or ‘normal’ level and secondly to ensure that any traces of the FODMAP just challenged have been removed from the gut before starting the next re-challenge. It can be hard for people to be ‘symptom free’ for 3 days so as long as they wait 3 days between each re-challenge and their symptoms have returned to a baseline level then that will suffice. Occasionally it may take longer than 3 days to obtain your baseline symptom level in which case 4 or 5 days may be required.

30. When experiencing moderate symptoms in a re-challenge it is suggested to either stop or continue depending on personal choice. If however moderate symptoms are experienced after the first day of re-challenging on the small portion, can you continue with an even smaller portion than that on the second day?

This is a really good question and doesn’t have a ‘correct’ answer. One suggestion is to half the portion size (of the small portion size) and re-challenge this on day 2. If symptoms occur again this usually indicates anxiety or something else rather than the FODMAPs causing symptoms. This is because the concentration of FODMAPs will be insignificant for the majority of portion sizes that small (half a small portion size). Some people are super sensitive to FODMAPs however and it may be best to stop the re-challenge. The same re-challenge can be attempted another time as tolerance levels can change over time and it is always worth trying again to liberate the diet from low FODMAP restrictions.

31. Can you incorporate successfully re-challenged high FODMAP foods into the diet as you continue re-challenging other high FODMAP foods?

I would recommend you stick to a strict low FODMAP diet throughout the re-challenging phase and only reintroduce high FODMAP foods once the re-challenging is complete. More often people find it is the overall load of FODMAPs rather than individual FODMAPs that increase symptoms. If you start to reintroduce FODMAPs while still testing tolerance levels to others you may start to consume an overall load of FODMAPs above what your body can tolerate and therefore increase the chances of experiencing symptoms.

32. Do I have to re-introduce garlic or onion as they do not agreed with me, would testing with garlic powder work I always cook with garlic powder?

If you do not like garlic or onion you do not need to reintroduce them. Instead choose one of the other fructan containing vegetables you would like to reintroduce. There is a complete table of vegetables that only contain fructans in the book which will help you make suitable choices. As you use garlic powder regularly you should challenge this, however I would not use garlic powder as an accurate test for working out tolerance levels to fructans found in vegetables. Instead treat the garlic powder as a separate test as the powder represents a concentrated form of fructans of unknown quantity. Finally it might still be worth you re-challenging the small portion size of garlic and onion. You may find you can tolerate this small portion size even though you think these vegetables do not agree with you. In the past you may simply have been eating too large portions of garlic and onion and this is worth getting a definitive answer to.


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