Dietary Interventions and IBS: What Really Works?

Low Fermentable Oligo-, Di-, Monosaccharides, and Polyols Diet

Half of IBS patients report that cereals trigger symptoms and 1/3 of them indicate fruits as triggers.^[11] Cereals, fruits, vegetables, legumes and dairy products contain FODMAPs, short-chain carbohydrates that have an osmotic action, are slowly absorbed in the small intestine and are fermented by bacteria. FODMAPs have a prebiotic action through oligosaccharides and are substrates for short-chain fatty acids (SCFAs), known for anti-inflammatory properties, hence supporting colonic health.^[12] A diet rich in FODMAPs increases the substrate for colonic fermentation with accumulation of water and gas resulting in colonic distention as well as resulting in mucosal inflammation and increased permeability, which impact colonic functions,^[13] resulting in abdominal symptoms, especially in patients with visceral hypersensitivity, like IBS.^[14,15] LFD results in less gas production and improvement of symptoms. Several studies revealed that following LFD, the density of enteroendocrine cells responsible for secretion of intestinal hormones is restored, with positive effects on symptoms and QoL.^[5]

LFD consists of two phases. In the first phase, foods containing FODMAPs are 'eliminated' for 4–6 weeks. In the 'reintroduction' phase (6–12 weeks), each food category is gradually reintroduced according to individual tolerance allowing a personalized LFD, which might be less restrictive, and, therefore, with fewer effects on intestinal microbiota. Patients whose symptoms fail to improve during the elimination phase, should stop the diet and look for alternative interventions.^[16]

Previous studies reported that LFD applied for short periods of time improved IBS symptoms in more than half of patients,^[17] and recent studies showed similar findings. A single-blinded RCT^[18] compared a structured individual low-FODMAP dietary (SILFD) advice with brief advice on a commonly recommended diet (BRD) in patients with moderate/severe IBS. With BRD, patients were instructed to reduce foods that can cause bloating/abdominal pain (fruits, vegetables, nuts, beans, garlic) and to avoid large meals. SILFD patients were instructed to replace high FODMAPs with low FODMAPS, and the number of high-FODMAP items per week diminished from 16 to 9. More SILFD patients reported a significant decrease in daily abdominal pain or discomfort compared to BRD patients. Compared to baseline, global IBS symptom severity score, abdominal pain and bloating significantly decreased in the SILFD group, but not in the BRD group, in parallel with a reduction in breath H₂ concentration.^[18]

An interesting paper comes from Gravina et al..^[19] After 6 weeks of LFD, IBS patients were instructed to gradually reintroduce small amounts of FODMAPs and were followed for 6 months. If symptoms reappeared with a certain FODMAP, the re-challenge was made with a lowered amount. Triggers reported were foods containing oxalate, hazelnuts, and chocolate in high amounts. The adherence to this protocol was very good. Both frequency and severity of symptoms significantly improved compared to baseline at all follow-ups.^[19] Thus, identifying and eliminating the trigger foods from the diet can control IBS symptoms in the long term. The well tolerated FODMAPs were re-included in the diet and further studies should see if this strategy has less harmful consequences on gut health.

Several meta-analyses confirmed the benefit of short-term LFD on IBS symptoms (especially abdominal pain and bloating) compared with control,^[16,20–23] but some authors acknowledged that the evidence was of a very low quality.^[16] LFD is currently included as a level B recommendation in the BDA guidelines for IBS.^[7]

There is accumulating evidence on the efficacy of LFD in IBS, with the proposal that it should become first-line treatment combined with other methods.^[3] Some IBS patients will not respond to LFD, and some will find it difficult to adhere to and maintain this diet. Besides, there are concerns about the detrimental long-term effects on the intestinal microenvironment and on nutritional status. Hence, most specialists prefer to recommend a healthy diet in everyday practice.^[5] Future research should focus on the long-term effects of a personalized LFD, excluding only those FODMAPs that trigger symptoms.