By Christian Shaw, ACP and specialist gastroenterology dietitian

The low FODMAP diet is a complex and restrictive approach which can be difficult to follow and may not be suitable for some patients.^1-3 Fructans are oligosaccharides which are reduced as part of the low FODMAP diet. Wheat is a major source of fructans in the UK and patients with IBS frequently report that wheat-based products induce their symptoms.^4-8 Could lowering fructan intakes be helpful for those with IBS? A gluten free diet (GFD) may be a way to achieve this, acting as a ‘bottom-up’ approach and recent evidence supports its use in IBS.⁹

Irritable bowel syndrome (IBS) is a disorder of gut-brain interaction (DGBI) with a global prevalence of 3.8% based on ROME IV criteria.¹⁰ The dietary management of IBS involves a 2-step approach using traditional or ‘first line’ dietary advice followed by the low fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAP) diet as ‘second line’ for those with ongoing symptoms.^11,12

What are FODMAPs? A re-cap

FODMAPs are short chain carbohydrates which are either slowly absorbed or escape digestion in the small intestine.¹³ As a result, some FODMAPs are osmotically active leading to increased intestinal water and distension, whereas others have a tendency to undergo fermentation in the distal small intestine and colon.^13,14 Both modes of action occur in healthy volunteers and those with IBS, but are thought to induce symptoms in IBS due to visceral hypersensitivity or a sensitive gut.^15,16 The current low FODMAP diet is a ‘top-down’ approach where all foods classed as high FODMAP are excluded. The response rate during short term restriction in IBS is 52-76%.^6-9,17-20 Therefore, it remains an effective approach for the majority of individuals with IBS.

 Concerns with the low FODMAP diet

Despite the effectiveness, the low FODMAP diet is a complex and restrictive approach, taking several months to follow it correctly across all 3 stages of the diet (restriction, reintroduction and personalisation).²¹ Evidence also suggests patients may struggle to follow this diet appropriately across these stages.^1,2 Tuck and colleagues (2019) noted that on average only 40% of patients using a low FODMAP diet were able to follow it across all 3 stages correctly, which was improved with dietetic support.² However, dietetic services in England for IBS vary and current provision may not be sufficient to meet service demand.²² Especially as the low FODMAP diet requires ideally 2-3 dietetic appointments to support patients.^21,23

• Initial appointment 45-60mins (FODMAP restriction)²¹

• Short term follow-up 20-30mins (FODMAP reintroduction)²¹

• Long term follow-up (FODMAP personalisation)

There is also concern that the restrictive manner of the low FODMAP diet may be harmful for those with a history of eating disorders or disordered eating.³ The prevalence of disordered eating amongst those with IBS is approximately 23-33%.^1,24,25 Patients may also follow restrictive diets in an attempt to manage their troublesome IBS symptoms, which can make the assessment between food avoidance due to symptoms or because of an underlying eating disorder difficult.²⁴ How best to identify such patients is not currently clear, but work is underway to provide guidance for clinicians. It has also been suggested that the low FODMAP diet should be a 4-stage diet, with an initial stage to check patient suitability before recommending the diet.³

Is it time to consider bottom-up approaches, such as single FODMAP exclusions?

In view of the concerns with a low FODMAP diet, could using a ‘bottom-up’ approach whereby a single FODMAP group is avoided based on suspected symptom triggers and dietary intake be a way forward for some patients? Thereby reserving a traditional low FODMAP diet for those with ongoing symptoms?

Patients with IBS associate symptoms with dietary triggers in 50-84% of cases^5,6 and wheat-based products are a suspected culprit in 14-53% of patients.^4-8

Wheat contains several possible offending components that may induce IBS symptoms.²⁶

• Gluten
• FODMAPs mostly fructans
• Amylase trypsin inhibitors (ATIs)

The main FODMAP in wheat is fructans, known as oligosaccharides, which represent the ‘O’ in FODMAPs and are fermentable short-chain carbohydrates.²⁷ Other common foods containing fructans²⁸ include:

• Onion
• Garlic
• Artichoke
• Leeks

Fructans consist of monomers of fructose (chains of fructose molecules) and are classified by their chain length (degree of polymerization; DP) and bonds present between the single sugar groups.²⁹

The main fructan groups^28,30,31 are:

• Inulin-type fructans (ITF) which includes:
• Fructo-oligosaccharides (FOS)
• Oligofructose

It should be unsurprising that fructans may trigger symptoms in IBS given that humans lack the intestinal enzymes required to breakdown these short-chain carbohydrates.¹⁴ As a result, fructans escape digestion and absorption, thereby undergoing rapid distal small bowel and colonic bacterial fermentation due to their short chain lengths.^32,33 It is well known that fructans have prebiotic effects, in which they undergo bacterial fermentation^15,16,29,32, leading to the generation of symptoms in those with IBS.¹⁶

Some studies prior to the development of the low FODMAP diet, explored fructans in IBS.^34,35 For example, in a retrospective study, patients with IBS and fructose malabsorption following a fructose and fructan restriction observed a 76% relief of gut symptoms.³⁴ A few years later, in a blinded challenge study, patients following a fructose and fructan restriction, were challenged with fructans which induced symptoms in 77%.³⁵ The authors acknowledged that applying these findings to only those with IBS and fructose malabsorption was unsound, given fructans are always poorly absorbed and have a potential to induce symptoms in the absence of fructose malabsorption in IBS.¹³

They later developed the low FODMAP diet by grouping other short chain carbohydrates together due to their similar physiological effects.¹³ However, this may not be entirely accurate, as the physiological effects may differ across the group, such as osmotic shifts being highest with fructose and polyols and the likely differing degrees of fermentation between fructans and galactans.^15,16,36 Due to the development of the low FODMAP diet as it is known today, it has been the main focus of research rather than individual FODMAPs.

One area which may provide insight into the potential of individual FODMAPs is the reintroduction stage of the low FODMAP diet, however data is limited.^37,38 A recent study published last year explored the reintroduction of high FODMAP foods via a mobile app.³⁷ Interestingly, the most commonly reintroduced foods were high fructan foods including wheat-based products, onion and garlic. This suggested that not only are these foods high on the agenda for patients with IBS, but were also most likely to be symptom triggers.

Overall, around 40% of individuals experienced symptoms following the reintroduction of these foods, including:

• Wheat bread (41%)
• Wheat pasta (41%)
• Wheat cereal (39%)
• Onion (39%)
• Garlic (35%)

A study published this year challenged patients with individual FODMAP powders during the reintroduction stage.³⁸ The results indicated fructans and mannitol were the most prevalent triggers, at 56% and 54%, respectively. To note, the fructan powder contained much higher amounts than usually obtained in the UK diet (20g/d vs. 4g/d³⁹), so the results do need to be considered with caution.

The largest contributor of fructans in the UK diet is from wheat-based products, given wheat is a dietary staple, providing around 66% of the overall fructan intake.^39,40 To note, GF grains and products are often lower in fructans.^27,39,41,42

• Wheat (1-4g fructan per 100g serving)
• Wheat bread (0.23-0.38g fructan per 2 slice serving)
• Gluten free bread (0.10g fructan per 2 slice serving)
• Gluten free pasta (0.19g fructan per 100g serving)
• Rice (trace amounts per 100g)

Could a GFD be helpful as a ‘bottom-up’ approach?

Given the potential for fructans to induce symptoms and as GF options are often lower in these short chain carbohydrates, could using a gluten free diet (GFD) as a ‘bottom-up’ approach be helpful in IBS?

The largest multicentre study to explore the low FODMAP diet at long term follow-up in 205 IBS patients, noted that many report using gluten and wheat free products.⁴³ Overall, 68% following the personalisation stage of the low FODMAP diet use these products and 43% choose gluten or wheat free options when eating out. Do patients use these products due to habit, or because they help to manage their IBS symptoms in the long term, through the reduction in fructans?

In 2022, the first randomised controlled trial (RCT) to explore a GFD for IBS showed this was an effective approach with a response rate of 58%. Furthermore, no statistically significant differences were seen in IBS symptom severity scores (IBS-SSS) when compared to traditional dietary advice (TDA) and a low FODMAP diet (p=0.43), suggesting all three diets were effective for IBS.⁹

To note, the GFD advised was a gluten reduction involving the avoidance of wheat, barley and rye, but permitted the use of ‘may contain’ products and cross contamination. Therefore, the approach was less strict than recommended in coeliac disease. The GFD led to a reduction in total fructans on average from 3.9 g to 2.4g/d (p=<0.01), supporting its use as a way to reduce fructans or as a ‘bottom-up’ approach and may explain the benefit seen.⁹

Studies implementing the restriction stage of the low FODMAP diet generally achieve total FODMAP intakes of less than 12 g/d.⁴⁴ As a result, <12 g/d was coined as the possible level of therapeutic benefit², but this has yet to be determined.³⁶ To note, studies exploring the low FODMAP diet at long term follow up, report much higher FODMAP intakes between 17-22 g/d^43,45,46, which is expected following the reintroduction of FODMAPs to tolerance. However, symptom benefit remains, with studies demonstrating a response rate of 57-60% at long term follow up.^43,46 Perhaps the degree of FODMAP restriction used currently as part of the low FODMAP diet is more stringent than required. However, studies exploring this or more FODMAP ‘gentle’ approaches⁴⁷ have yet to be conducted.

Rej and colleagues (2022) noted FODMAP intakes using a GFD reduced from 27.4 g to 22.4 g/d (p=0.03) and also using a TDA from 24.9 g to 15.2 g/d (p=<0.01), suggesting both diets are a form of FODMAP gentle.⁹ There also appears to be a trend for fructans to remain reduced at long term follow up⁴⁴, suggesting fructans may be a major player inducing symptoms in IBS. Although, individual tolerance may vary and a strict low FODMAP diet may be required to identify FODMAP triggers initially.³⁸

Nonetheless, could a GFD be offered to patients as a bottom-up approach to reduce fructans in those reporting wheat as a trigger and driven by patient choice⁴⁸, reserving the low FODMAP diet for suitable patients who have ongoing symptoms?  A GFD is well known by the public⁴⁹, whereas a low fructan diet is likely not. Considering this, using a GFD to lower fructans may be a practical approach patients can follow. Patients choosing to use a GFD could be encouraged to reintroduce gluten and wheat containing foods to check tolerance, similar to the process used for fructans during the reintroduction stage of the low FODMAP diet. This would help to prevent unnecessary restrictions in the long-term.

References

Written in collaboration with Dr Schär

Disclaimer: This blog has been written in collaboration with the nutrition team at Dr Schär and reviewed by the MyNutriWeb nutrition and dietetic team. Approval of each sponsor and activity is carefully assessed for suitability on a case by case basis. Sponsorship does not imply any endorsement of the brand by MyNutriWeb, its organisers, its moderators or any participating healthcare professional, or their association. Sponsorship funds are reinvested into the creation and promotion of professional development opportunities on MyNutriWeb.

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