Research on the reintroduction phase of the low FODMAP diet

With the low FODMAP diet still being relatively new, there is limited research on the  three different phases of the diet. By the way if you hadn’t realised there are actually 3 stages to the low FODMAP diet then please read the article linked here Following the low FODMAP diet long term…What is a modified FODMAP diet?

There is a lot of research on the first phase which is termed ‘FODMAP Restriction’ (commonly referred to as the low FODMAP diet). However the most limited research is on phase 2 ‘FODMAP Reintroduction’ (the food challenge phase) and phase 3 ‘FODMAP Personalisation’ (which is when you create your own personalised and modified version of the low FODMAP diet including high FODMAP foods to personal tolerance).

Research on Reintroducing FODMAPs


goyal 2021

Low fermentable oligosaccharide, disaccharide, monosaccharide, and polyol diet in patients with diarrhea‐predominant irritable bowel syndrome: A prospective, randomized trial (available here)

The first long term RCT into the low FODMAP diet. Also the first study in a northern Indian population. 101 IBS-D patients  (58% male) diagnosed under Rome IV underwent either a 4 week FODMAP Restriction diet followed by a 12 week FODMAP Reintroduction protocol or ‘traditional diet advice’. Both severity of symptoms and quality of life significantly reduced in both the FODMAP and traditional diet groups although significantly more patients responded to FODMAPs vs traditional diet.

Of note the traditional dietary advice group was advised to eat small frequent meals, have adequate fluid intake, reduce alcohol, tea, and caffeine intake, decrease fat and spicy food, and limit high-fibre food and resistant starch intake which is based on NICE and BDA Guidelines. The same instructions were continued till 16 weeks.

Advice for the FODMAP Reintroduction phase was based on the paper by Tuck & Barrett 2017 (see 2017 below). “Briefly, patients were instructed to undertake 3-day FODMAP food challenge, using one food at a time, and have 3-day “washout” period in between. When tolerance to each subgroup was checked, patients were asked to assess tolerance to larger doses, increased frequency, and combinations of high FODMAP foods”.



Adherence and Effects Derived from FODMAP Diet on Irritable Bowel Syndrome: A Real Life Evaluation of a Large Follow-Up Observation (available here)

Similar to Harvie et al 2017 the authors found the FODMAP restriction phase of the low FODMAP diet improves symptoms (abdominal pain, bloating, flatulence, diarrhoea and constipation) in 102 patients with IBS under Rome IV diagnosis and this improvement can be maintained 6 months after reintroducing FODMAPs. Unlike the other papers listed here a gastroenterologist rather than a dietitian gave dietary instructions to patients. According to the authors only 4 patients did not adhere to the FODMAP Reintroduction stage while >90% of patients were adherent to the entire low FODMAP diet.

Nawawi et al 2019

Low FODMAP diet significantly improves IBS symptoms: an Irish retrospective cohort study

Nawawi, K.N.M., Belov, M. & Goulding, C. Low FODMAP diet significantly improves IBS symptoms: an Irish retrospective cohort study. Eur J Nutr 59, 2237–2248 (2020). 

A very detailed dietary and symptoms’ history was taken, thus allowing the dietician to target the specific FODMAP groups that needed to be eliminated for each individual. The majority of patients needed to eliminate oligosaccharides, but only approximately a half had to eliminate polyols and monosaccharides, while a quarter had to eliminate disaccharides. Thus, a detailed history taken by our FODMAP-trained dietician allowed her to give each patient an individual, tailored diet. Thus, each patient only had to eliminate the FODMAP groups which they personally had difficulty in digesting, as had been identified by the dietician.

It was aimed to re-introduce the high FODMAP foods at this initial follow up 3 months after commencing the low FODMAP diet; however, some patients had already inadvertently tried the high FODMAP foods. Many of these had experienced a return of their symptoms and were reluctant to re-introduce high FODMAP again so soon. For those who reported good symptomatic improvement, they were counseled regarding systematic re-introduction of the high FODMAP food as per the KCL FODMAP re-introduction booklet. With reintroduction you introduce one item at a time, over a gradual, slow period, e.g., starting with a 1/3 of an apple on the first day up to a full apple on day 3. For those who were reluctant to re-introduce high FODMAP foods at this point, we commenced them on probiotic yogurts with bifidobacteria or supplements of bifidobacteria as a study by Staudacher et al. have shown that low FODMAP diets reduce luminal bifidobacteria [13]. At each follow-up visit, all patients were encouraged to re-introduce high FODMAP foods.

The majority of patients had an improvement in their IBS symptoms by 3-month follow-up. In these patients, they were offered and counseled regarding the concept of re-introduction of the high FODMAP foods. However, not everyone was willing to be ‘re-challenged’, as they felt so well on the low FODMAP diet and were concerned that their symptoms would return on re-challenging. Of 127 patients, 14 patients were re-introduced with high FODMAP foods. All of them maintained their symptomatic response at 3-month post re-introduction (6-month follow-up) of the high FODMAP foods (p value < 0.0001 for combined symptoms when compared to the baseline score). Of all 14 patients, 7 patients remained under the dietician follow-up at 12 months (9 months following re-introduction of the high FODMAP foods) and they were able to maintain their longterm symptomatic response. The remainder of the patients continued to restrict some high FODMAP foods, but not all the high FODMAP foods. As with the initial diet being tailored to each individual patient, so was the re-introduction.

In this study, a large proportion of patients (n = 60/74 at 6-month followup and n = 29/41 at 12-month follow-up) were still on the low FODMAP diet, mainly due to the recurrence of symptoms. This indicates that a longer duration of the low FODMAP diet might be feasible for some patients if not all. It is important to note that although the symptoms
were not fully resolved with longer follow-up duration (i.e., mean symptom score of zero/near-zero), the patients were still able to maintain their symptomatic improvement (i.e., mean symptom scores were about the same as the previous one).

Re-introduction of the high FODMAP foods occasionally can be difficult due to the patient’s fear of symptoms recurrence. As in this study, only 14 patients were re-introduced with the high FODMAP foods, after having symptoms improvement at 3-month follow-up. After the re-introduction of the high FODMAP foods, all the mean scores of individual and combined symptoms remained low at 6- and 12-month follow-up (when compared with scores at 3-month follow-up), as well as the symptomatic improvement remained statistically significant (when compared with baseline symptoms scores). This showed that the re-introduction of the high FODMAP foods is achievable, but will need good patients’ education and support from a dedicated dietician.


Tuck &amp; Barret 2017 Reintro

Re‐challenging FODMAPs: the low FODMAP diet phase two

Tuck, C., and Barrett, J. (2017) Journal of Gastroenterology and Hepatology3211– 15. doi: 10.1111/jgh.13687.

“The re‐challenge phase is crucial to assist patients in identifying specific dietary triggers, reduce the level of dietary restriction required, and increase prebiotic intake. Limited evidence is available to guide best practice, but, in practice, beneficial outcomes can be seen through strategic food reintroductions. Here, we set out some practical recommendations based on clinical experience. Dietitians should tailor the challenge process to the individual patient and their needs”.

Long‐term impact of the low‐FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndrome

Long‐term impact of the low‐FODMAP diet on gastrointestinal symptoms, dietary intake, patient acceptability, and healthcare utilization in irritable bowel syndrome (available here)

When I worked at King’s College London I was fortunate enough to lead on the first ever long term study in the UK looking at the reintroduction phase of the low FODMAP diet. I found that the vast majority of people, after completing the low FODMAP elimination diet, continued to follow a modified version of the low FODMAP diet after reintroducing FODMAPs. Importantly 71% of these people continued to have relief of their IBS symptoms after completing the reintroduction phase and had excellent food related quality of life measures. This is the first evidence to show that you do not need to continue to follow the low FODMAP elimination diet to provide effective IBS symptom relief and you can include high FODMAP foods (after completing the reintroduction phase) without this affecting your IBS symptoms. Some other important questions this research helped to answer included:

1. Do people reintroduce FODMAPs after starting a low FODMAP diet?

YES! In fact 97 out of 103 people completed the reintroduction phase.

2. What sort of diet do people follow in the long term after completing the low FODMAP restriction diet and the reintroduction phase?

Out of the 103 participants when followed up one year later:
78 of them continued to follow an adapted low FODMAP diet. Meaning they had reintroduced FODMAPs to their own tolerance levels.
19 followed a normal diet. Meaning they had reintroduced FODMAPs and no longer followed any FODMAP restrictions.
6 continued to follow a low FODMAP restriction diet in the long term (a year later).

Therefore the vast majority of people do reintroduce FODMAPs but continue to follow a modified low FODMAP diet as their normal diet.

3. After you have reintroduced FODMAPs do you still have relief of your IBS symptoms in the long term?

YES! There are two statistical points here. First of all 61% of people found relief of their IBS after following a low FODMAP restriction diet. This is similar to other studies looking at the effectiveness of the restriction phase of the low FODMAP diet. Importantly in those 61% of people 70% of them continued to have relief of their symptoms a year later.

This shows that in the vast majority of people who find the low FODMAP restriction diet effective, even once they have reintroduced FODMAPs they still have relief of their IBS symptoms in the long term.


Click the ddf image below to link to the original abstract from 2015

I presented the study at the Digestive Diseases Federation (DDF) research conference in July 2015. The full paper was published in 2017 and you can access the full article here.

A nice review of this research is also provided on the Monash FODMAP website titled Low FODMAP diet provides both short- and long-term relief of gut symptoms.


Long-term irritable bowel syndrome symptom control with reintroduction of selected FODMAPs

Long-term irritable bowel syndrome symptom control with reintroduction of selected FODMAPs (available here)

This study demonstrated that a reduction in FODMAPs improves symptoms and quality of life in IBS (predominately IBS-D) and this improvement can be maintained long term (6 months) after reintroducing FODMAPs.

This study was based in a ‘real-world’ clinical environment with participants being advised by registered dietitians. It adds to the body of evidence that a dietitian delivered low FODMAP education is effective at reducing symptom severity in IBS patients.

Similar to previous research they found a reduction in the energy consumption and especially the fibre intake to below recommended amounts during the restriction phase of the low FODMAP diet. However, with the reintroduction of FODMAP foods to tolerance, especially galacto-oligosaccharides (GOS) and fructans, the fibre intake increased and the food consumption became nutritionally adequate again. This important finding highlights the need for this diet to be supervised by an experienced dietitian, especially during the re-challenge phase.

Overall this study has shown that dietitian delivered dietary education during the re-challenge and reintroduction phase of the diet leads to increased FODMAP intake without significant worsening of symptoms.


Randomised clinical trial: the efficacy of gut-directed hypnotherapy is similar to that of the low FODMAP diet for the treatment of irritable bowel syndrome (available here)

Although this study was a comparison of the low FODMAP diet vs gut-directed hypnotherapy the long term follow up period was 6 months. As such the participants reintroduced FODMAPs and this study provides 6 month long term data after the reintroduction phase. The general conclusions from this study include similar gastrointestinal symptom improvement from gut‐directed hypnotherapy compared to the low FODMAP diet. While unsurprisingly hypnotherapy had superior efficacy to the diet on psychological indices. No additive effects were observed when these treatments were combined.

Regarding the reintroduction of FODMAPs. Participants followed the low FODMAP diet for 6 weeks and if symptoms improved were instructed to complete FODMAP Reintroduction, which the paper provides details on. 60 out of 62 completed the FODMAP reintroduction phase meaning they had reintroduced high FODMAP foods to personal tolerance and were consuming a modified FODMAP diet. Only 2 participants continued on a strict FODMAP restriction diet.

Therefore the results from this study are similar to the two studies mentioned above (Harvie et al 2016 & O’Keeffe et al 2017). In that the vast majority of participants were able to successfully complete FODMAP reintroduction when educated by a dietitian and importantly maintained symptomatic benefits when liberalising their diet with high FODMAP foods.

Follow-up of patients with functional bowel symptoms treated with a low FODMAP diet (available here)

This study included one hundred and eighty patients who had attended outpatient clinics for low FODMAP dietary advice. 131 (73%) had IBS and 49 (27%) had IBD (inflammatory bowel disease) with IBS symptoms. After finishing the low FODMAP diet and reintroduction the patients were sent questionnaires, on average 16 months later, to obtain information on symptoms and other outcomes.  So what were the results 16 months later?

In the long term (~16 months) the greatest reduction in symptoms were seen in bloating (82%) and abdominal pain (71%).  The vast majority of patients (84%) consumed a modified low FODMAP diet where some foods high in FODMAPs were reintroduced. While 16% continued to follow the low FODMAP elimination diet with all restrictions. Wheat, dairy products, and onions were the foods most often not reintroduced by patients. The interesting and important point here, as I found in the study I completed at King’s College London, is despite reintroducing FODMAPs the majority of patients still reported satisfaction with the modified FODMAP diet and had control of their symptoms.

This is an important study as it is the largest study to look at the efficacy of the low FODMAP diet in the long term (16 months after initial treatment). It provides evidence that for long term self management of IBS symptoms the reintroduction of FODMAPs leading to a modified low FODMAP diet is an effective treatment and highlights the importance of the reintroduction phase in achieving this. The lack of validated resources to measure the outcomes will make it difficult to compare the results obtained to other research using validated measures.


The low FODMAP diet improves gastrointestinal

The low FODMAP diet improves gastrointestinal symptoms in patients with irritable bowel syndrome: a prospective study (available here)

This was the first study to look at long term effects of the low FODMAP diet following reintroduction. Ninety patients with a mean follow up of 15.7 months were studied. It is not clear whether patients followed a complete reintroduction protocol and therefore managed to personalise their diet by consuming a modified FODMAP diet. The authors mention that after 6 weeks on a low FODMAP diet patients were ‘provided with written information concerning the limited reintroduction of restricted group of carbohydrates’. However 22 out of the 90 patients did not receive this information. The study mentions the majority of patients (75.6%) were adherent to the diet at long term follow up but it is not clear if this is to a low FODMAP or modified FODMAP diet.  Most patients (72.1%) were satisfied with their symptoms in the long term with abdominal pain, bloating, flatulence and diarrhoea significantly improved. The authors did not evaluated the effectiveness of the low FODMAP diet at 6 weeks, only at a mean of 15.7 months. Overall not much can be taken from this study. Despite having a long term follow up there is a lack of information on what the long term diet consisted of and confusion over how many patients reintroduced FODMAPs and what the method was for achieving this.


Food Choice as a Key Management Strategy for Functional Gastrointestinal Symptoms (available here)

Food choice as a key management strategy for functional gastrointestinal symptoms

One of the first review papers discussing the FODMAP dietary treatment and therefore not surprisingly the first paper to provide details on the FODMAP reintroduction process. I have included the above paper in this article due to this reintroducing information which is shown in the image above. The FODMAP reintroduction method discussed in the paper is one of several ways suggested to reintroduce FODMAPs. Until research is completed that focuses on the best way to reintroduce FODMAPs there will always be different interpretations of how to reintroduce. My opinion is the method described in the paper has a few faults which may cause some individuals increased difficulty when reintroducing FODMAPs and therefore they may fail to reintroduce FODMAPs properly. You can read more about this and other potential unsuitable FODMAP reintroduction methods in the article ‘Planning on reintroducing FODMAPs? Be aware of misinformation!

As new research is completed and published, this post will be updated with the most recent evidence.

Due to the lack of research on the reintroduction stage it means as dietitians we have to use the research literature available combined with our knowledge of elimination diets (such as the low FODMAP diet) and IBS symptom management to help create an effective FODMAP reintroduction plan.
If you are unable to see a dietitian to help you with the reintroduction phase of the low FODMAP diet you must make sure you get all the necessary information (and support) to give you the best chance of successfully reintroducing FODMAPs. To start with read the research linked on this page which is often available as ‘open access’. There are of course some really useful articles freely available on the internet. There has even been one brief review article on Re‐challenging FODMAPs: the low FODMAP diet phase two.
The Re-challenging & Reintroducing FODMAPs book I published brings all the current evidence and best practice together into a self help guide to provide extra help for those completing the reintroduction phase whether they have dietetic support or not.