There is growing evidence that a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) improves symptoms in irritable bowel syndrome (IBS) patients. We aimed to retrospectively investigate the effects of this diet in Irish IBS cohort over a 12-month follow-up period, including after re-introduction of the high FODMAP foods.
All the tertiary referrals seen by an FODMAP-trained dietician were reviewed (2013–2016). Patients were evaluated for IBS symptoms by a questionnaire (four-point Likert scale). Subsequently, advice regarding the low FODMAP diet was given. Symptoms’ response was assessed at 3-, 6-, and 12-month follow-up, by use of the same questionnaire. Re-introduction of high FODMAP foods was aimed to commence at the subsequent follow-up.
A total of 164 patients were identified. Thirty-seven patients were excluded due to failure to attend for follow-up. Hundred and twenty-seven patients (77% patients, of which 85% were female) completed the initial 3-month follow-up. Forty-five percent (74/164) and twenty-five percent (41/164) of the patients had continued follow-up at 6 and 12 months, respectively. Of the 127 patients who returned for follow-up, their commonest baseline symptoms were lethargy (92%), bloating (91%), flatulence (91%), and abdominal pain (89%). All symptoms were significantly improved at the initial follow-up (p < 0.0001 for all). Most patients (66%) were satisfied with their overall symptoms control. In patients who had a longer follow-up duration, all symptoms remained significantly improved compared to the baseline (p < 0.0001 for combined symptoms at 6 and 12 months). After re-introduction of the high FODMAP foods, all patients maintained their symptomatic response (n = 14/14 and n = 7/7 at 6- and 12-month follow-up, respectively). The best symptoms’ improvement was seen in those who were fully adherent to the FODMAP diet.
In this Irish retrospective cohort study, the low FODMAP diet significantly improved all IBS symptoms at 3-, 6-, and 12-month follow-up. Following the re-introduction of the high FODMAP foods in a subgroup of patients, they were able to maintain their long-term symptomatic response up to 9 months. The low FODMAP diet might be continued for longer than 3 months; however, further studies are needed to assess the long-term safety of this diet.
Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder with a prevalence in the general population estimated to be between 10 and 25% [1,2,3,4,5]; depending on the diagnostic criteria used and the geographic region. A recent meta-analysis showed a pooled estimate of the global prevalence of 11.2% . IBS is characterised by abdominal pain with associated change in stool frequency and/or stool consistency . Yet, most of the IBS patients do suffer from other GI symptoms as well, such as abdominal bloating, dyspepsia, excessive flatulence, faecal urgency, and tenesmus. IBS is often seen as a benign and harmless condition. However, in reality, it can be debilitating and difficult to treat. For many years, management of IBS has been directed towards lifestyle change (exercise, healthy diet, and regular meals) and medications (laxatives, antispasmodics, and antidepressants). Although these measures can be helpful, IBS patients often remain symptomatic. Some dietary modifications have been suggested based on the hypothesis that certain foods can trigger IBS symptoms. These include lowering the fat content and optimising fibre intake. However, this is often of little or no benefit .
In 2004, a group of researchers from Monash University introduced a term FODMAP, which stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols . It is a group of poorly absorbed carbohydrates thought to contribute to the GI symptoms in IBS. One of its hypothesized mechanisms is bacterial fermentation of the undigested FODMAP; which then produces short chain fatty acids and gases, and subsequently triggers GI symptoms (abdominal pain, bloating, and flatulence). It is likely that other factors such as stomach/bowel motility, visceral hypersensitivity, and gut microbiota play a role in this mechanism as well . In the last 13 years, some observational studies and randomized trials investigating the effect of the low FODMAP diet have been conducted. In general, there is growing evidence that the low FODMAP diet is effective in reducing GI symptoms in IBS patients, although one could argue the validity of some of those studies, due to a small number of participants, poor response rate, and variation in dietary advice and symptoms assessment .
IBS is common in Ireland, even though the exact prevalence is unknown. Unfortunately, until now, there is a scarcity of published data on the efficacy of the low FODMAP diet in the Irish population with IBS symptoms. Therefore, we aimed to retrospectively investigate the effect of the low FODMAP diet on IBS symptoms in an Irish cohort. Furthermore, we aimed to assess the symptoms response at longer follow-up periods (3, 6, and 12 months), including after re-introduction of the high FODMAP foods.
Materials and methods
We had retrospectively identified 164 consecutive adult patients with IBS (2013–2016), who had been referred to an FODMAP-trained dietician in University Hospital Galway, Ireland. All the patients had been initially assessed either by gastroenterologists or by surgeons before being referred to the dietician. In this study, IBS was defined as the presence of any of the following GI symptoms for more than 6 months: abdominal pain, abdominal bloating, excessive flatulence, and change in stool frequency/consistency, in the absence of any organic cause. Patients with underlying GI disorders such as inflammatory bowel disease (IBD) and coeliac disease were included as well, provided that they were in remission (normal C-reactive protein level for IBD and normal IgA tTG level for coeliac disease). None of the patients had tried the low FODMAP diet prior to the meeting with the dietician.
This is a retrospective cohort study. All the consultation cards (under one FODMAP-trained dietician) from January 2013 until March 2016 were reviewed. Data were collected at the initial dietetic consultation and subsequently at 3-, 6-, and 12-month follow-up.
In 2013, a dietician who had received training from Kings College London (KCL) on implementing the low FODMAP diet commenced this dietary intervention in University Hospital Galway in an out-patient setting. The aim was to use a detailed dietary and symptomatic history to allow the dietician to tease out the specific FODMAP groups that each individual had difficulty digesting and thus which ones to eliminate. Using KCL guidelines, similar to those out-lined by Barrett et al., the FODMAP diet is not a ‘one-size fits all’ and should be tailored for each individual . Patients were followed up every 3 months for up to a year to ensure that the diet was being followed effectively and also remained nutritionally adequate.
Initial dietetic consultation
All the relevant demographic data and medical/surgical history were collected on the initial consultation. Patients were asked regarding their symptoms, any previous treatment and dietary habit. Important blood results such as full blood count, renal function, electrolytes, inflammatory markers, and coeliac serology were also checked and recorded. 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. Questions were also asked in relation to the patients’ diet from a general health point of view, and therefore, those with a high sweet/sugar intake were advised to reduce this, as a general health measure. Those patients deemed suitable for the low FODMAP diet were counseled on the principle of the diet. List of foods in both the high and low FODMAP groups was given to the patients. Information booklets regarding the low FODMAP diet, published by KCL, were given to the patients. Each initial consultation lasted approximately for 1 h.
First follow-up (2–3 months)
The aim was to have the first follow-up visit 2 or maximum 3 months after the initial visit as the KCL guidelines’ suggestion, and we should aim for re-introduction of high FODMAP foods after 2–3 months. During the first follow-up session, patients were asked to complete the same questionnaire to asses change in symptoms. In addition, their feedback on implementing the low FODMAP diet was obtained and their adherence was recorded. It was aimed to re-introduce the high FODMAP foods at this initial follow-up; 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 re-introduction 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 . At each follow-up visit, all patients were encouraged to re-introduce high FODMAP foods.
Subsequent follow-ups (6 and 12 months)
After the first follow-up session, patients were seen again at 6 and 12 months, and on each occasion, they filled out the same questionnaire in relation to symptoms. Each subsequent follow-up consultation lasted approximately 30 min.
Adherence to the low FODMAP diet
Adherence to the diet was assessed and recorded during each follow-up session. The adherence was recorded by a combination of patient food and symptom diary and dietary recall on detailed questioning from the dietician. The patient was considered to have full adherence if he/she was taking the low FODMAP foods without concurrent high FODMAP foods’ intake, as per their own tailored diet. Partial adherence was defined as any concurrent intake of the high FODMAP foods while on the low FODMAP diet over the entire period of the diet.
Patients’ symptoms were assessed during each dietetic consultation using a symptom evaluation form; developed by the KCL group. Patients were asked to rate the severity of their symptoms (abdominal pain, bloating, increased flatulence, belching, abdominal gurgling, faecal urgency, incomplete evacuation, nausea, heartburn, regurgitation, and lethargy) using a four-point Likert scale (0 = no symptom, 1 = mild, 2 = moderate, 3 = severe). The severity of the symptoms was graded based on the frequency and to what extent they affect the patient’s social activities; none = no symptoms or very rarely, mild = occasional symptoms, moderate = frequent symptoms that affect some social activities and severe = continuous symptoms that affect most social activities. Patients also were asked regarding their satisfactory relief of the overall symptoms and stool consistency according to Bristol Stool Chart (Fig. 1).
In this study, we had excluded the analysis of two symptoms, namely, belching and abdominal gurgling, since they are not commonly associated with IBS. Improvement of patients’ symptoms was also assessed according to the adherence to the low FODMAP diet. For this analysis, improvement in symptom scores was defined as at least one-point reduction in the Likert scale.
All data were analysed using Minitab version 17. Demographic data and baseline symptoms were analysed descriptively. Normality testing was performed, and the symptoms data were normally distributed. For analysing the change in symptom severity, the individual scores for each symptom were added and the means calculated. Means scores at the follow-ups were compared with the baseline using paired t test. A p value of less than 0.05 was considered as significant and all p values were two-tailed.
A total of 164 patients with IBS symptoms were identified. Thirty-seven patients were excluded due to failure to attend their first follow-up review. The majority of the included patients had failed first-line pharmacological treatments such as anti-spasmodic agents, peppermint oil and antacids. Hundred and twenty-seven (77.4%) patients completed the initial 3 months follow-up. Seventy-four (58%, 74/127) and forty-one (32%, 41/127) patients had continued follow-up at 6 and 12 months, respectively. The median age of the study cohort was 45 years (16–80), with 85% (n = 108) being female. The median duration of IBS symptoms taken from baseline (at initial consultation) was 24 months (6–456). As shown in Table 1, some patients had underlying GI disorders: 16% had coeliac and 22% had IBD. However, their underlying GI disorders were in remission, which had been confirmed by normal blood tests (C-reactive protein for IBD and anti-tTG for coeliac disease). For the baseline symptoms, most common IBS symptoms were abdominal bloating (91%), flatulence (91%), and abdominal pain (89%). 92% of the patients complained of lethargy (Table 2).
All baseline symptoms were significantly improved at the initial follow-up (3 months), with p values of less than 0.0001 for all the symptoms (Table 3). In patients who had a longer follow-up period, all symptoms remained significantly improved at 6- and 12-month follow-up when compared to the baseline. When assessing the overall response (composite score of all symptoms) to the low FODMAP diet at 3 months, 87.4% (n = 111) patients were classified as responders (defined as at least one-point reduction in the Likert scale, as compared to baseline), while 12.6% (n = 16) were non-responders (equal or worsening total points). Figure 2 depicts the effect of the low FODMAP diet on the patients’ stool consistency after 3-month implementation. Approximately half of the patients had improved stool consistency, i.e., Bristol stool type 3 and 4 (61% for patients with initial Bristol stool of types 5–7 and 47% for patients with initial Bristol stool of types 1–2). Most patients were satisfied with their overall symptoms’ improvement following the implementation of the low FODMAP diet (66%, n = 86/127 at 3 months, 72%, n = 53/74 at 6 months, and 76%, n = 31/41 at 12 months).
At 3-month follow-up, most patients were able to adhere to the low FODMAP diet (n = 97, 76%) (Fig. 3). Symptoms’ improvement correlated very well with the adherence, as shown in Fig. 4. A higher percentage of symptoms improvement was seen in those patients who were fully adherent to the low FODMAP diet, as compared to those with partial adherence.
A sub-analysis was performed on 80 patients after excluding those with coeliac disease and IBD. The improvement remained significant for each individual symptom as well as the total symptoms (p < 0.001 for 3-month analysis—Table 4). When examining the coeliac disease/IBD cohort (n = 47), the low FODMAP diet was found to be beneficial as well by significantly improved all the baseline symptoms at 3-month follow-up (p < 0.001) (Table 5). After applying the ROME IV criteria to our study cohort, 99 patients met the diagnostic criteria with 58 patients had diarrhoea-predominant IBS (IBS-D) and 41 patients had constipation-predominant IBS (IBS-C). A sub-analysis of this ROME IV-defined IBS patients showed similar significant symptomatic improvement in all symptoms across the 12 months follow-up period, except for the heartburn which was not improve at 12 months when compared to the baseline (n = 30 patients) (Tables 5, 6).
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 long-term 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 (Fig. 5).
In this Irish retrospective cohort study, our study cohort was representative of IBS patients seen in tertiary referral centres. As a result, they tend to be those who have experienced longer duration and more severe symptoms, compared to typical IBS patients seen in primary care. Consistent with the previous epidemiological IBS studies , the majority of our patients were female (85%). In this study, we did not strictly apply the ROME criteria for IBS in our inclusion criteria, since in the ‘real world’, IBS patients do complain of various upper and lower GI symptoms. Fifty percent of our patients had underlying GI disorders such as coeliac disease, diverticular disease, Crohn’s disease, and ulcerative colitis (Table 1). We also did not exclude this subgroup of patients, since IBS symptoms often co-exist with other GI disorders. However, we did exclude any patients with active underlying GI disorders, based on clinical suspicious of GI symptoms (e.g., rectal bleeding in inflammatory bowel diseases) and biochemical markers, namely, C-reactive protein and anti-tTG. Interestingly, only 6% of the total patients had been diagnosed by their GP with anxiety and/or depression, although some studies showed that nearly, half of IBS patients had concurrent anxiety and/or depression . Most of the patients (approximately 90%) had baseline symptoms of flatulence, abdominal bloating, and abdominal pain. Nearly, 80% of them had baseline bowel symptoms, specifically, faecal urgency and incomplete evacuation. Although upper GI symptoms (nausea, heartburn, and regurgitation) are not included in the diagnostic criteria of IBS, they occurred relatively common in our IBS patients (50–57%). Unsurprisingly, most of the patients reported feeling lethargic due to their ongoing problematic IBS symptoms (92%).
Our study showed that the low FODMAP diet significantly improved all the IBS symptoms, upper GI symptoms, as well as patients’ energy level. This was true for all the follow-up periods, which were at 3, 6, and 12 months. This finding was in keeping with meta-analysis done by Marsh A et al. that showed a significant decrease in IBS Symptoms Severity Score (IBS SSS) for those individuals on the low FODMAP diet in both randomized clinical trials (OR 0.44, CI 0.25–0.76, p = 0.00) and non-randomized interventions (OR 0.03, CI 0.01–0.2, p = 0.02). When looking at the individual symptoms, the low FODMAP diet was also found to significantly reduce symptom severity for abdominal pain, bloating, and overall symptoms with OR of 1.81, 1.75, and 1.81, respectively. In addition, in Marsh’s study, they found that the IBS quality-of-life score was improved significantly with low FODMAP diet (RCTs: OR 1.84, CI 1.12–3.03, p = 0.39; non-RCTs: OR 3.18, CI 1.60–6.31, p = 0.89) .
Fundamentally, the low FODMAP diet is intended to be a short-term exclusion/restricted diet, usually for 2–3 months, before the patients are re-introduced back with the high FODMAP foods. However, in our study, a large proportion of patients (n = 60/74 at 6-month follow-up 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). Despite the feasibility of the low FODMAP diet for a longer duration, there is a concern regarding the depletion of nutrition due to the restriction of those carbohydrates in FODMAP. Staudacher et al. had suggested that FODMAP restriction leads to lower calcium intakes in the short term . In addition, a recent study found that the low FODMAP diet was associated with reduced abundance of colonic bacteria . Having said that, a prospective cohort study by O’Keeffe et al. involving 103 IBS patients did show a favourable long-term impact (18 months) of the low FODMAP diet on GI symptoms in 57% of patients. In addition, the study revealed that long-term nutritional adequacy was not compromised when compared with the ‘habitual’ diet group . Nonetheless, before the practice of long-term low FODMAP diet can be formally advised, further studies regarding the safety of long-term low FODMAP diet should be carried out. In regard to non-dietary, non-pharmacological interventions for IBS, there was an interesting study (randomized clinical trial) comparing the effects of gut-directed hypnotherapy (GDH) to the low FODMAP diet on GI symptoms. Peters et al. found that durable effects of GDH were similar to those of the low FODMAP diet for the relief of GI symptoms. However, the true effects of GDH remain uncertain, since the sample size was quite small (25 hypnotherapy, 24 diet and 25 combination), and further studies are needed .
Adherence to the low FODMAP diet is quite challenging due to the change in foods choice. Nonetheless, our adherence rate (76% at 3-month follow-up) was satisfactory and comparable to the previous clinical trials . When we looked at the effect of diet adherence on symptoms change, the best symptoms’ improvement was seen in those who were fully adherent to the diet (Fig. 4). 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.
The fact that only 14 patients managed to achieve a re-introduction of the high FODMAP foods made us consider other issues at play. The gut bacterium Oxalobacter formigens (OF) which plays a key role in digesting high oxalate foods is rapidly declining in the Western world. Liu et al. showed that > 50% of young adults in the US are deficient. Although there is nil in the literature in relation to IBS and Oxalobacter, our dietician found through her detailed dietary history that many patients appeared to have their symptoms triggered by foods high in oxalate. This was purely observational, and as the study progressed our dietician starting asking those who were having a sub-optimal response to the FODMAP diet about intake of high oxalate containing foods and symptoms. Those who appeared to have their symptoms aggravated by high oxalate containing foods were then advised to restrict these. As mentioned, this was only observational, but may be an area for future evaluation. As a general health measure, those with a high sweet intake had been asked to restrict these and some of these patients reported an improvement in their symptoms. It could be postulated that this may be related to the fact that sugar is the preferred substrate for yeast growth; however, as their sugar restriction commenced at the same time as the FODMAP diet, it is hard to tease out the exact impact of the high sugar intake.
There were some limitations to our study. It is a retrospective study; therefore, any association between the low FODMAP diet and symptoms change, might not be as accurate as randomized controlled trial. Possible recall bias due to the use of questionnaire in evaluating symptoms improvement might distort the results. Another limitation was the variable duration of patients’ follow-up. This limitation can be addressed by increasing the sample size and conducting a prospective study. We deliberately did not use a formal IBS diagnostic criterion such as ROME IV to screen our participants. This is because in reality, patients do suffer more diverse GI symptoms. Nevertheless, our study included a relatively large number of participants (n = 127, for the initial follow-up period—3 months). Albeit, a smaller number of participants at subsequent follow-up at 6 and 12 months, we managed to show a continued symptomatic response in patients who stayed on the low FODMAP diet. By recruiting a single FODMAP-trained dietician, who was skilled in assessing and delivering dietary advice and support eliminates any heterogeneity in the intervention.
In this Irish retrospective cohort study, the low FODMAP diet significantly improved all IBS symptoms at 3-, 6-, and 12-month follow-up. Following the re-introduction of the high FODMAP foods in a subgroup of patients, they were able to maintain their long-term symptomatic response up to 9 months. We have also shown that the low FODMAP diet might be continued for longer than 3 months; however, further studies are needed to assess the long-term safety of this diet, as it might affect patients’ nutritional status as well as gut microbiota.
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We would like to acknowledge the rest of the team members in the gastroenterology unit and the nutrition and dietetic department, for their support and assistance with the study.
Conflict of interest
The authors declare that there are no conflicts of interest to disclose.
This study had been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.
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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). https://doi.org/10.1007/s00394-019-02074-6
- Irritable bowel syndrome
- Low FODMAP diet
- Retrospective study