Re-Challenging and Reintroducing FODMAPs: The How, When, and Why

I was originally asked (back in January 2017) by Nutrition 411, an American dietetic website, to write an article on the second and most important phase of the low FODMAP diet, the FODMAP Reintroduction Phase. Nutrition 411 is a peer-to-peer network and sister brand of Consultant 360. The website was launched in 2006 and hosts content written by dietitians for dietitians. The article was a massive hit with over 10,000 people reading the article in one year and I have re-produced the article below with a few updates. For the original article on Nutrition 411 follow the link here or click on the image below. A dietitian from Nutrition 411 also reviewed my book ‘Re-challenging & Reintroducing FODMAPs‘ and you can read their review here.

Click the image to be taken to the original article


Re-Challenging and Reintroducing FODMAPs: The How, When, and Why


The low FODMAP diet has been a revelation in treating the symptoms of irritable bowel syndrome (IBS). The efficacy of the low FODMAP diet has been reported in several observational studies with robust evidence provided from a small number of randomised control trials (RCTs). Overall these studies suggest the low FODMAP diet is effective in reducing IBS symptoms in 50-80% of people.  However, studies have also indicated that a diet low in FODMAPs alters the gastrointestinal microbiota in the short term in a potentially negative way. The long-term effects of these changes to the microbiota are currently unknown, and to prevent unnecessary restriction of high FODMAP foods long term, the reintroduction of FODMAPs is recommended. Currently there is limited research on reintroducing FODMAPs and a lack of accurate and up-to-date information available to help practitioners. This article will describe the most current accepted way of re-challenging and reintroducing FODMAPs as part of the reintroduction phase.


Before discussing the reintroduction phase, it is first worth remembering that the low FODMAP diet actually comprises three distinct phases:

The Three Phases of the FODMAP dietary treatment
The Three Phases of the FODMAP dietary treatment. Click the image to learn more…

Research has focused on phase one, the low FODMAP restriction (or elimination) diet, which is defined by the restriction of the intake of high FODMAP foods. Typically, the restriction phase is recommended to be followed for 2-6 weeks with RCTs showing clinically significant reduction in symptoms after 3-4 weeks. Individuals can follow the low FODMAP diet for longer; however, the aim of the restriction phase is to reduce symptoms. Therefore, the important point is individuals only need to follow the low FODMAP diet until they achieve a reduction in symptoms.

The second phase is reintroduction, which itself is split into two phases and consists of re-challenging high FODMAP foods to personal tolerance levels. The next step is reintroducing these tolerated high FODMAP foods back into the diet. The re-challenge phase has a general consensus on how it should be implemented and it will be discussed in the next section.

The third phase of the low FODMAP diet comprises the long-term self-management of IBS symptoms. More long-term research is required as evidenced by two recent studies that found the vast majority of individuals who have previously followed a low FODMAP diet and completed the reintroduction phase continue to follow a modified low FODMAP in the long term. A modified low FODMAP diet can be defined as a diet that contains high FODMAP foods reintroduced to the individuals’ personal tolerance levels. Despite the reintroduction of high FODMAP foods, individuals are still able to maintain adequate control of their IBS symptoms.


Re-challenging and reintroducing FODMAPs: the recommended approach

Once an individual has reduced their IBS symptoms by following a low FODMAP restriction diet, they are ready to start re-challenging FODMAPs. The aim of the re-challenge phase is to discover the individuals’ personal tolerance levels to FODMAPs, for which everyone will have a different tolerance level. Certain principles should be followed when re-challenging FODMAPs. These principles help ensure the re-challenging process can be as systematic and accurate as possible in helping to identify the specific FODMAP or FODMAPs which trigger symptoms.

Main principles of re-challenging FODMAPs

  • The low FODMAP restriction diet must be followed during the entire re-challenging phase. For example, this means even if an individual tests fructose and does not experience any symptoms, they still do not reintroduce fructose-containing foods until after they have completed all the re-challenges.
  • There are up to 10 main re-challenges to be completed. The FODMAPs fructose, lactose, galacto-oligosaccharides (GOS), sorbitol, and mannitol require one re-challenge each, while fructans require five re-challenges (one fruit, two vegetable, and two cereal and grain) as shown in the table below. The reason fructans have five re-challenges is due to the wide variety of foods containing fructans and the differences in FODMAP content between these food groups. As there are 10 re-challenges, with each re-challenge lasting six days, it usually takes 10 weeks to complete all the re-challenges.
  • It is best to follow a systematic protocol for re-challenging. The two most commonly used protocols are a three-day re-challenge test phase followed by a three day “washout” period. An alternative-day protocol can be followed where you re-challenge a FODMAP every other day followed by a three day “washout” period. The “washout” period is designed to ensure that any symptom effects from the FODMAP that has just been tested does not interfere with the next re-challenge. Ideally, the individuals symptoms are reduced back to a baseline level (preferably being symptom free) before starting the next re-challenge.
  • Portion sizes of the FODMAP should be incrementally re-challenged over three days. Previously, advice may have recommended the same portion size be used for every re-challenge. The issue with this approach is it may be difficult to accurately test tolerance levels to FODMAPs if you are only eating the same portion size every time. Additionally, if you start with a portion size too high in FODMAPs then it will be more likely symptoms will occur. This could lead an individual to restricting their intake of all foods containing that FODMAP as they believe it triggers symptoms, when in fact they may be able to consume smaller portion sizes of that FODMAP without symptoms.
  • Only re-challenge a food that contains one type of FODMAP. Past recommendations for re-challenge foods included using mushrooms or apricots. Mushrooms, however, contain significant levels of both fructans and mannitol, so if symptoms are experienced, it would be unclear if it were the fructans or the mannitol triggering the symptoms. Apricots are high in both sorbitol and fructans, once again confusing the effects of two FODMAPs, making it difficult to determine which FODMAP triggers symptoms. Examples of suitable foods are presented in the table below; however, an individual’s likes, dislikes, and normal dietary habits must be considered when choosing appropriate foods for re-challenging.


Example of foods containing one individual FODMAP suitable for re-challenging tolerance levels*

Re-Challenge Food No. of Test Days FODMAP
Avocado Up to 3 sorbitol
Chickpeas Up to 3 GOS
Garlic Up to 3 fructan
Honey Up to 3 fructose
Onion Up to 3 fructan
Milk Up to 3 lactose
Persimmon Up to 3 fructan
Sweet potato Up to 3 mannitol
Wheat bread Up to 3 fructan
Wheat pasta Up to 3 fructan


At the end of re-challenging, an individual should have a better awareness of which FODMAPs trigger symptoms, what their tolerance levels are to individual FODMAPs, and what portion size can be consumed before triggering symptoms. This is important, as it helps with long-term self-management of IBS symptoms and increasing the variety of foods consumed. It is important to note that these are guidelines and individuals must adapt the information to suit their needs, preferably with the help of a registered dietitian nutritionist. Dietetic input during the reintroduction phase has shown good efficacy, although completing the reintroduction phase without dietetic advice has not been evaluated.

Reintroducing FODMAPs

Following the re-challenging process, high FODMAP foods can be reintroduced into the diet gradually at the discovered tolerance levels for each individual. When reintroducing FODMAPs back into the diet, an individual is consuming combinations of high FODMAP foods as well as increasing their overall load of FODMAPs. Overall, the more FODMAPs consumed, the more likely symptoms will occur; to help manage this the process, the individual needs to become aware of their FODMAP threshold, which describes the amount of overall FODMAPs that can be consumed before triggering symptoms. This is different from FODMAP tolerance levels, which describe tolerance to individual FODMAPs. Everyone will react to FODMAPs differently; some will be super sensitive and have a low FODMAP threshold, while others may be able to consume some FODMAPs every day without triggering symptoms as they have a high FODMAP threshold.

No “testing” is involved in this process, and individuals will need to discover their FODMAP threshold through a trial-and-error process and by assessing their symptom reactions. It is an ongoing process and often leads to a long-term diet consistent with a modified low FODMAP diet as described in the introduction.


*Note: A complete list of foods high in one FODMAP with suggested portion sizes for re-challenging and tables detailing foods containing multiple FODMAPs can be found in the book Re-challenging and Reintroducing FODMAPs. The portion sizes are based on published research and data from the Monash University low FODMAP diet app (see Acknowledgements below) which provides information on the FODMAP content of foods. The “principles” for re-challenging are expanded in the book and the protocol that can be followed is provided in a flowchart. The re-challenging protocol is adapted from low FODMAP training courses and literature provided by King’s College London University in the United Kingdom (see Acknowledgements below). Further explanations on everything discussed in this article are expanded in the book Re-challenging and Reintroducing FODMAPs.


References and recommended reading


Gibson PR, Shepherd SJ. Food choice as a key management strategy for functional gastrointestinal symptoms. Am J Gastroenterol. 2012;107(5):657-66; quiz 667. doi:10.1038/ajg.2012.49.

Halmos EP, Christophersen CT, Bird AR, Shepherd SJ, Gibson PR, Muir JG. Diets that differ in their FODMAP content alter the colonic luminal microenvironment. Gut. 2015 Jan;64(1):93-100. doi:10.1136/gutjnl-2014-307264.

Maagaard L, Ankersen DV, Végh Z, Burisch J, Jensen L, Pedersen N, Munkholm P. Follow-up of patients with functional bowel symptoms treated with a low FODMAP diet. World J Gastroenterol. 2016 Apr 21;22(15):4009-19. doi:10.3748/wjg.v22.i15.4009.

O’Keeffe M, Jansen C, Martin L et al., (2018Long‐term impact of the low‐FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndromeNeurogastroenterol Motil 30, e13154.

Staudacher HM, Irving PM, Lomer MC, Whelan K. Mechanisms and efficacy of dietary FODMAP restriction in IBS. Nat Rev Gastroenterol Hepatol. 2014;11(4):256-66. doi:10.1038/nrgastro.2013.259.

, The low FODMAP diet in the management of irritable bowel syndrome: an evidence‐based review of FODMAP restriction, reintroduction and personalisation in clinical practiceJournal of Human Nutrition and Dietetics31, 2(239-255)(2018).



The Monash Uni low FODMAP diet app. Monash University website. Accessed March 17, 2018.

FODMAP research teams’ Reintroducing FODMAPs booklet and the low FODMAP diet for functional gastrointestinal disorders training course only available to registered dietitians. King’s College London website. Accessed March 17, 2018.


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