Irritabel tarmsyndrom

The effect of a low FODMAP diet in patients with irritable bowel syndrome

Isabel Bråthen, MSc Clinical Nutrition, Myrens Ernæring _____________________________________________________________________________________________

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, which have a significant impact on patients’ quality of life. Up until recently there have been few satisfactory treatments available, however today it is a growing interest and a growing body of evidence to support the effect of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs). Several observational studies and one thorough randomized-controlled trial, shows positive correlations between a low FODMAP diet and symptom palliation in IBS patients. This paper will review IBS and the role of FODMAPs in the line of treatment.


Irritable bowel syndrome is a very common gastrointestinal disorder, which can interfere with quality of life and also contribute to a financial burden on society due to IBS patients being absent from work and the high consumption of healthcare resources (1, 2, 3). In fact, IBS is the most common disorder seen in the gastroenterological practice (4). The prevalence of IBS varies from 5-30% worldwide, and the great variation range can be explained by the fact that different studies use different criteria for definitions on diagnosis (5, 6, 7, 8). Overall, the disorder is more prone to occur in women than in men, and is often diagnosed in adulthood somewhere between 20-50 years of age (9, 10, 11, 12, 13, 14) To date there is no biochemical, histopathological or radiological test to diagnose IBS, since there are no abnormal pathology (15). IBS is assessed based on symptoms, and exclusion of other possible diagnosis (3). The need for a tool to diagnose the disorder resulted in the developing of clinically useful definitions in order to classify the syndrome and the severity of it. Today The Rome criteria (I, II and III) are in use to diagnose IBS (16, 17, 18).

IBS patients are often categorized into sub-groups depending on different bowel patterns. There are four subtypes they can be divided into according to the Rome III criteria: diarrhoea-predominant (IBS-D), constipation-predominant (IBS-C), a mixture of diarrhoea and constipation (IBS-M) and unclassified IBS (U-IBS) (3, 17). As a result, there is no typical clinical picture other than abnormalities in the gastrointestinal tract (19). Symptoms range from diarrhoea to constipation, abdominal pain, distension, bloating, nausea and flatulence (15) (5). The degree of symptoms varies tremendously from patient to patient. Some can have tolerable symptoms, while others may have severe. It is also typical that some patients live with daily symptoms, while others describe intermittent intervals of symptoms (9, 13).

Although IBS is counted for being the most frequently seen gastrointestinal disorder, therapy has not been satisfactory (20). Health professionals eventually recognized what patients had been saying all along; the food is playing a compelling role in their symptoms, and the body of significant literature is now growing (21, 22). Furthermore, over 60% of IBS patients report aggravation of symptoms after ingestion of food, ranging from within 15 minutes and 3 hours postprandial (23). Therefore, recent interest has focused more on dietary approaches towards the therapy aspect of IBS. There is a diet that has gained great consideration, a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (1). FODMAPs are believed to be an important trigger for gastrointestinal symptoms (15).

FODMAPs and the FODMAP diet
There is no indication or observations demonstrating that food allergy or intolerance are the cause of IBS symptoms (24). The symptoms may be similar, however the reaction IBS patients may experience to certain foods has been suggested to originate from poorly absorbed carbohydrates such as FODMAPs (25). These carbohydrates include fructose, lactose, fructans, and galactans and sugar alcohols, such as sorbitol, maltitol, mannitol, xylitol and isomalt.

Fructose is typically found in pears, honey, apples, melons, dried fruit and juice. Lactose is presented in milk and milk products. When it comes to polyols, it is common to find it in low calorie/sugar free products. Galactans and fructans are found in common foods such as wheat, rye, onions, cabbage, garlic, artichokes, legumes, soy, asparagus, insulin, lentils, broccoli, leeks and sprouts (see table 1.) (26, 27, 28, 29, 30, 31).

There are several reasons why the various FODMAPs cause problems in the intestines. Firstly, they are poorly absorbed in the small intestine due to the slow and poor capacity for transport across the epithelium. Secondly, they can have an osmotic effect by drawing water into the intestines and create a laxative effect. And last, because of their short chain length they get faster fermented by bacteria and provide gas production in the large intestine, resulting in abdominal distension and increased intraluminal pressure, which in turn can cause discomfort or pain (3, 32, 33). Therefore, a consensus has grown towards hope of a possibility of alleviating symptoms in IBS patients, by introducing a low FODMAP diet as a possible treatment (1).

The FODMAP diet is organized as a strict exclusion period of virtually all FODMAPs for a period of 2-8 weeks. The farther the exclusion period is, the better to get control over symptoms and whether they do subside or not. Furthermore, the diet is followed by a rechallenge period where various groups of FODMAPs and food products are introduced one at a time and monitored for symptoms. It is not the intention that the patient should avoid all FODMAPs forever, therefore the rechallenge period let the patient find out what they respond to and how much they can tolerate (34, 35). Since there are individual tolerances and differences within each sub-group for various FODMAPs, patients are encouraged to for example, not completely refrain from fruit, but rather choose fruit with low content of FODMAPs (26, 36, 37).

Although some may have relief in symptoms, patients should not be given promises of a cure (33). In order to get a more thorough overview of what impact a low FODMAP diet can offer IBS patients, it is important to understand the results of previous studies.

As previously mentioned, many IBS patients report that there are specific foods that causes them to react. (38). Studies show that IBS patients often avoid these foods consciously, and most of the avoided food actually belongs to the FODMAP family (3). The effect of diets where one excludes different sugars still remains questionable, as some researchers publish significant clinical improvement, while others do not (39). To date, there are few studies that have suggested clear indications that a low FODMAP diet will have a therapeutic effect on IBS (1). However, Ong and colleagues assessed breath hydrogen while they tested IBS patients versus healthy volunteers. Intake of a low FODMAP diet gave significant reduction of breath hydrogen production in the volunteers and a tremendous reduction in breath hydrogen plus IBS dominant symptoms in those with IBS (15). A significant rise in breath hydrogen following ingestion of the test sugar demonstrates poor absorption (34). Breath hydrogen testing helps to identify which sugar that gives the most ailments. Today, this method is used more and more (40).

Studies have proposed that three out of four patients with IBS will benefit greatly from the restrictions of FODMAPs (22). The potential benefits that can be achieved for IBS patients who follow a low FODMAP diet was first observed in a retrospective study in which IBS patients responded well on a diet low in fructose and fructans. The study showed that 74% of the patients reported improvement (41).

The interesting findings were a few years later supported by a randomized, placebo-controlled trail conducted by Shepherd et al. They wanted to validate the previous findings and see whether the participant’s symptoms came back if they were exposed to the different FODMAPs again and also if they only could see effect on fructose compared to other sugars. The study recruited 25 IBS patients according to Rome II criteria, and they had all tested positive for breath test in addition to having responded well to a diet low in FODMAPs. Participants randomly received fructose, fructans, fructose + fructans or placebo. Readmission of symptoms were reported by 70% of those who received fructose, 77% of participants who received fructans and 79% of those who received fructose + fructans. By comparison, only 14% reported symptoms in the placebo group. They also recorded a dose-response relationship, as they observed that the symptoms increased in line with the dose of FODMAPs they received. Few studies have completed such trails, so the evidence is limited, however this study provides strong and significant reasons to believe that a diet low in FODMAPs can improve symptoms and quality of life in the majority of IBS patients (22).

IBS patients have shown to produce more hydrogen gas than healthy controls, regardless of FODMAP content (15).
The breath tests can reveal intolerances in IBS patients, respectively fructose, lactose, and sorbitol. However, it is important to remember that there still are other sugars, which can cause symptoms. Fructans and galactooligosaccharides will not be breath tested, since they are always malabsorbed and should therefore always be considered as triggers for IBS patients (34).
The advantage to undergo a breath test is that one can determine which sugars that give the most symptoms. That prevents unnecessary limitation of foods that is basically well tolerated and helps individualizing the diet (34). Nevertheless, studies show that it is more common to have combined sugar malabsorption than isolated sugar malabsorption (18).

Many patients are convinced that they neither tolerate milk or gluten, and tend to avoid foods with those present. Therefore associations between IBS, lactose intolerance and celiac disease (CD) have recently received much attention (32). Misdiagnosis can insofar go both ways, since overlapping of symptoms is observed (29, 30, 42). For example, lactose intolerance may in some cases be present, however the symptoms can on the other hand be due to malabsorption of other carbohydrates (43). Given that the symptoms are similar, there is reason to believe that CD may be a common factor in IBS, but studies find no mechanisms for this (34). Several patients reported improvement by excluding gluten from the diet. Some suggests that the relief of symptoms is only due to a placebo effect, conversely there is greater reason to believe that this can be explained by other content such as wheat and other grain products (44). Nevertheless, what has been established is that CD patients develop symptoms due to gluten allergy (protein), whereas IBS patients react to sugar polymers as fructans and galactans (carbohydrates) (42, 45, 46). Looking at the opposite; patients who actually have CD can be misdiagnosed with IBS due to vague CD symptoms (29, 30). Therefore it is important that doctors or dietitians exclude CD or other diseases before they set diagnosis, and that they know how different diseases are excluded (34).

In order for the FODMAP diet to be successful and for the results to be trustworthy, patients are recommended to receive adequate education and information about the diet, and a professional dietician should monitor them. It is recommended to introduce a patient to a low-FODMAP diet in an individual consultation with a dietician, since symptoms vary between patients, and they have different tolerances, due to variances in intestinal flora (1, 32). Moreover, a consultation also allows diet modifications to be individualized so that a balanced diet can be provided (1). Education through group sessions has been performed, however with apparent success (21, 41). During the individual consultation, the dietician should spend a substantial time analysing the patient’s existing diet, describe the physiology of malabsorption, and demonstrate portion sizes of high fructose load foods, cooking tips and quick snack ideas (21). In addition it is highly necessary to inform about food alternatives in order for the patient to maintain nutritional adequacy (21). Ostgaard et al. studied the effects of guidance on diet management, and found that patients without guidance seek alternatives that do not always fulfil daily needs (47). One finding was that only one third of milk related products were consumed, when compared to the control group, while replacements consisting of soy, rice and oat milk products were chosen instead. However, as a result of these replacements, the unguided patients received under their minimum daily calcium intake, as well as a significantly lower intake of riboflavin than recommended. Moreover, the study also reported a significantly lower intake of retinol equivalent, β-carotene and magnesium in the unguided group, due to a lower consumption of vegetables such as broccoli, onion, garlic, paprika and tomatoes. It has also been observed that patients often avoid foods that contain components that are important for health as phosphorus and vitamin B2 (47). Furthermore, one can also see low intake of fiber (33). However, total energy, protein, fat and non-starch polysaccharides intakes seem to be satisfactory even at a low FODMAP diet (26).

The guided IBS patients on the other hand, reported intake of sour milk containing probiotics twice as often as unguided patients. The relationship between FODMAPs and IBS ailments like bloating, are associated with the patients intestinal flora. The presence of large amounts of Clostridium spp., which breaks down FODMAPs, can have great significance since breakdown of FODMAPs results in gas production (3, 32). It has been observed lower amounts of Lactobacillus spp. and Bifidobacterium spp. in IBS patients compared with healthy patients. Lactobacillus spp. and Bifidobacterium spp. do not produce gas, nor ferment on carbohydrates and can therefore be beneficial for IBS patients to take as supplements (48, 49). Interestingly, some FODMAPs may have prebiotic effect, which leads to further growth of for example Bifidobacterium spp. Therefore, patients should try to gradually reintroduce FODMAPs to its acceptable level (26, 34). Consuming probiotics may then help guided IBS patients to increase their tolerance to FODMAPs compared to unguided patients.

This shows the downside of dealing with IBS without guidance; the risk of avoiding important food sources, or consuming food items rich in FODMAPs without knowing it, compared to a guided management of a diet, with an improved healthier diet and reduced IBS symptoms (47).
So despite the fact that IBS patients are shown to be perceptive about food consumption, they are aware of the fact that food intake triggers symptoms, it is still too extensive to control at all time, and too complex to identify all FODMAPs and their effects. Patients are suggested to search assistance from a dietician in order to obtain an optimal FODMAP diet. Guidance will also help patients long-term. Ostgaard et al. also found that patients, 2 years after their guidance on diet management, had changed their dietary intake. They had a reduced consumption of food rich on FODMAPs, more food with probiotic supplements was consumed, and they avoided less food sources important to their health. Again, resulting in reduced IBS symptoms and improved quality of life (47).

Another limitation with the low-FODMAP diet in regards to compliance is that IBS patients need to know what kind of foods that are low in FODMAPS, since the content are no place listed or defined (1).

The low FODMAP diet has a limited, yet growing body of results supporting its efficacy. Studies have shown a significant association between food and symptoms in patients with IBS (26). The complex disorder is now more understood, and we can therefore draw more conclusions on what kind of diet that can be beneficial for IBS patients and why.

When possible, and in order to gain fulfilment, a low FODMAP diet should be done with help of a qualified and trained dietician (1, 26). Although research that has been done has shown striking results, there is still a need for more research, and randomized controlled trials over a longer time period should be pursued. We also need more research to determine which patients that can benefit from this diet and also to quantify the FODMAP content of various foods in for example a data base, which will help patients follow this diet more effectively (1, 26). Finally, we need the diet to be more available as well as understandable in order for patients to successfully adhere to the FODMAP regime.

With lack of other or better targets to relief symptoms in IBS patients, the low FODMAP diet should be considered as a first-line therapy (20).


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