A Low FODMAP (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) Diet Update by Erin Balodis, MSc, ND

Abstract

Since their introduction into the nutrition world in the mid 2000s, fermentable carbohydrates, commonly knowns as FODMAPs have gained significant interest for their application as a low FODMAP diet to help those suffering with bowel disorders. Irritable bowel syndrome has a significant and growing prevalence around the globe, with limited successful interventions. However, following a low FODMAP has shown remarkable benefit. Low FODMAP foods contain low levels of fermentable and prebiotic fibers, which raise concerns of overall gut health, in those eating a low FODMAP diet since it is established that these fibers contribute to a healthy microbiome. This is one of a number of concerns surrounding the use of the low FODMAP diet for those suffering from bowel disorders, discussed below.

Introduction

Following a diet low in fermentable carbohydrates, now commonly known as the low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) diet, has gained popularity since its introduction to the nutrition world in the mid 2000s (Gibson and Shepherd 2005). Over the past 16 years the mechanisms of action, food content of FODMAPs, efficacy of the diet, as well as doubts and concerns have been extensively studied. Much of the research has been focused around solidifying the hypothesis that following a low FODMAP diet (LFD) benefits those with irritable bowel syndrome (IBS). The use of the LFD in other bowel disorders including inflammatory bowel disease (IBD) is increasing. While results have been promising, as with many medical advances there can always be drawbacks, the LFD not being an exception.

As review, FODMAPs can be found in a range of very common foods such as fruits, vegetables, legumes and cereals, honey, milk and dairy products, and sweeteners. All FODMAP are potential triggers, but fortunately, not all FODMAPs aggravate the same symptoms in patients with irritable bowel syndrome (Bellini et al 2020). Food processing techniques, plant cultivars, and growing conditions can all impact the FODMAP level in foods (Varney et al 2017). Monash University researchers were the first to come up with extensive lists of the content of FODMAPs in foods. Researchers around the globe have continued to study the content of FODMAPs in foods which is important to facilitate nutrition intervention and therapies (Liljebo et al 2020) and to be able to apply the diet internationally (Varney et al 2017).

Low FODMAP in Irritable Bowel Syndrome

The prevalence of IBS is estimated to be 11% globally, and much higher in certain countries including Canada and the United States (Canavan et al 2014). While not life threatening, it is well established that the effects of IBS significantly impact the quality of life of those that suffer from it. The LFD has been a beacon of hope for people with IBS, especially since many identify food as trigger for symptoms, but dietary interventions were not always a first line treatment.

Up to 80% of people with IBS feel benefit when following a LFD (Hustoft et al 2017). Three meta-analyses have shown that a diet low in FODMAPs effectively reduced functional gastrointestinal symptoms in those with IBS and is safe for short term use (Marsh et al 2016, Schumann et al 2018, Varjú et al 2017). Dionne and colleagues (2018) also found that a LFD is effective in reducing global symptoms in IBS patients, but they reported the evidence is ‘very low quality’. In a recent study, the LFD was shown to specifically improve IBS symptoms such as abdominal pain, bloating, stool consistency, perceived severity of disease, and physical and mental components of quality of life; particularly in patients who suffer from diarrhea predominant IBS (IBS-D) patients (Cingolani et al 2020). The same researchers suggested the LFD seems to show greater feasibility for patients with more time to dedicate to the diet, more motivation, and more severe clinical features. This is a common concern with regard to the LFD, that it is time consuming and difficult to follow (Weynants et al 2020).

Due to the increase in popularity of the low FODMAP diet for the management of IBS, it is often self-prescribed and self-led. Sometimes it is suggested by general practitioners or gastroenterologists, however, evidence supports the use of dietitian-led education, in both individual and group delivery models (O’Keeffe and Lomer 2017). The 2019 Canadian Association of Gastroenterology Clinical Practice Guideline for the Management of IBS document states that “If a low-FODMAP diet is suggested, it should be implemented under the guidance of a dietician, and a strict diet should be implemented for as short a term as possible (e.g., four weeks)” (Moayyedi et al 2019). In a qualitative study by Trott and colleagues (2019), patients with IBS that were provided LFD information from their GPs and gastroenterologists reported that the information provided was difficult to apply in “real life”. One major concern without proper education and guidance is the length of time that people will continue with the LFD and the downstream consequences that may occur. In a review by Whelan and colleagues (2018) three phases of a LFD are outlined; FODMAP restriction; FODMAP reintroduction; and FODMAP personalisation (Whelan et al 2018). They suggest that it is important for doctors, dietitians and patients to appreciate that this is not a ‘diet for life’ but, instead, an approach to dramatically reduce FODMAP intake below the level at which they induce functional gut symptoms. Dionne and colleagues (2018) report that LFD exclusion for two to six weeks should be viewed as a diagnostic test to identify IBS patients who are sensitive to FODMAPs. Those who fail to improve should not continue the diet. Those who improve should be instructed on reintroducing foods which contain FODMAPs to determine their personal sensitivities and tolerance thresholds. This information should then be used to liberalize and personalize the low FODMAP diet with the intention of improving adherence and minimizing effects on the gut microbiome. In a randomized double blind, placebo-controlled study by Hustoft and colleagues (2017), a LFD improved symptoms in patients with IBS after only three weeks.

Among the concerns of adhering to a LFD long term are the potential changes in colonic microbiota composition. The LFD is by nature a diet low in prebiotic fibers and has been shown to reduce intake of prebiotic fructans and galacto-oligosachrrides (GOS) from the diet by up to 50 % (Böhn et al 2015, Staudacher et al 2012). These non-digestible carbohydrates typically increase the levels of bifidobacteriaceae and lactobacillaceae families in the gut of healthy individuals. Not surprisingly, following a LFD can cause a reduction in bifidobacteria and an increase in bacteria associated with dysbiosis (Vandeputte and Joossens 2020). After only four weeks of following the LFD, Staudacher and colleagues (2012) saw a significant reduction in luminal bifidobacteria concentration. Halmos and colleagues (2015) found a reduced total bacterial abundance in the feces by an average of 47% (when compared to a typical Australian diet). Vandeputte and colleagues (2020) suggest that supplementation with probiotics could be considered to partly counteract these changes. In a 2017 randomized controlled trial, researchers gave patients eating a LFD two sachets of multi-strain probiotic daily (450 billion bacteria per sachet) or placebo sachets, and found that those in the treatment group had greater abundance of Bifidobacterium species, and reported ‘adequate symptom relief’ more than patients receiving the placebo (Staudacher et al 2017). Some studies have shown that short-chain fatty acids (SCFAs) may also be negatively affected after following a LFD (Hustoft et al 2017), however, other studies have found no effect (Halmos et al 2015).

Nutritional Adequacy

An often-cited concern of the LFD is nutritional inadequacy, most notably, total energy, carbohydrate, fiber, calcium and iron (Hill et al 2017 , O’Keeffe et al 2018, Staudacher et al 2012). In 2020, Staudacher and colleagues conducted a secondary study of two randomized controlled trials where they looked at the habitual nutrient intake, diet quality, and diversity in participants with IBS and the effect of a four-week LFD on these parameters compared with controls. They concluded that in IBS, many individuals failed to meet national recommendations for a number of nutrients, including fat, fiber, iodine, and selenium. A LFD, when delivered by a dietitian, did not significantly impact the intake of most nutrients or diet diversity, however, it led to lower diet quality compared with controls (Staudacher et al 2020). Diet quality was a measure of how closely the diet aligns with dietary guidelines, based on World Health Organization dietary guidelines for the prevention of chronic disease.

Another concern of adhering to a LFD is a possible reduction in fiber intake if whole grain wheat products and high FODMAP fruits and vegetables are not replaced with suitable alternatives. A decrease in dietary fiber can lead to, or exacerbate, constipation especially in those with IBS. Research results are very mixed, with some studies showing that the LFD does indeed lead to a decrease in fiber intake (Böhn et al 2015), while others showed no difference (Eswaran et al 2016). Harvie and colleagues (2017) found that during the LFD, fiber intake decreased below 30 grams per day for males, and 25 grams per day for females, which is below the recommended numbers for many countries, including Canada. However, they did note that once study participants re-introduced FODMAPs to a tolerable level, fiber content of the diet returned to pre-intervention levels.

Low FODMAP Diet in Inflammatory Bowel Disease

While the majority of research surrounding the LFD is in regard to IBS, there have been an increasing number of studies looking at its effects in patients with IBD. In 2009, a pilot study by Gearry and colleagues showed that the low FODMAP diet may be the first effective dietary therapy for patients with IBD with coexistent functional gut symptoms. Interestingly, a randomized, placebo-controlled, cross-over re-challenge trial by Cox and colleagues (2017) found that of the FODMAPs examined it was fructans, but not GOS and sorbitol that induced gastrointestinal symptoms in patients with quiescent IBD. Since the initial pilot study, other research has shown similar findings of benefits of the LFD in IBD (Bodini et al 2019, Testa et al 2018). Similar to the LFD in IBS, it has also been suggested that the LFD be dietitian assisted, and only used short term (Pedersen et al 2017). In 2019, Bodini and colleagues found that in those with IBD, following a LFD was associated with an amelioration of fecal inflammatory markers. Shortly after in 2020, another study, specifically in people with ulcerative colitis, showed that consumption of a LFD might decrease systemic and intestinal inflammation (Milajerdi et al 2020). Similar to the concerns expressed for the use of the LFD in those with IBS, researchers in IBD suggested caution should be exercised due to the possible loss of prebiotic effects and nutritional adequacy (Colombel et al 2018, Halmos et al 2016).

Criticisms of the Low FODMAP Diet

Besides the aforementioned concerns of a LFD in both those with IBS and IBD, additional concerns have been mentioned. In a 2021 study by Weynants and colleagues, despite the fact that the long-term adherence and satisfaction of a LFD was high in patients with IBS, they indicated that it is difficult to follow. In one study, 64% of people thought the LFD diet was more expensive (Gearry et al 2009). Study participants reported that applying the LFD had negative impacts on their family and social life (Trott et al 2019). Following a LFD accentuated the participants sense of being excluded from communal events involving food and “such events needed to be navigated rather then enjoyed” (Trott et al 2019). Mari and colleagues (2018) showed greater adherence to a low-FODMAP diet is associated with eating disorder behaviour and suggest that in clinical practice it is important for a clinician to have a suspicion of eating disorders in IBS patients when a high level of LFD adherence is achieved.

Conclusion

The LFD has shown increasing evidence for use as short-term dietary treatment for those with IBS. Research has indicated that due to a number of concerns over nutritional adequacy, it should be led by a qualified health professional, well versed in the intricacies of the LFD. Taking a probiotic while adhering to a LFD and ensuring proper reintroduction is done to liberalize the diet are suggested to counter some of the negative effects the diet can have on the colonic microbiota (Halmos et al 2015, Staudacher et al 2017). It seems that there is not yet enough robust evidence to support the use of the LFD long-term.

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