Food intolerances are estimated to affect up to 20% of the population but complete understanding of diagnosis and management is complicated, given presentation and non-immunological mechanisms associated vary greatly. This review aims to provide a scientific update on common food intolerances resulting in gastrointestinal and/or extra-intestinal symptoms. FODMAP sensitivity has strong evidence supporting its mechanisms of increased osmotic activity and fermentation with the resulting distention leading to symptoms in those with visceral hypersensitivity. For many of the other food intolerances reviewed including non-coeliac gluten/wheat sensitivity, food additives and bioactive food chemicals, the findings show that there is a shortage of reproducible well-designed double-blind, placebo-controlled studies, making understanding of the mechanisms, diagnosis and management difficult. Enzyme deficiencies have been proposed to result in other food sensitivities including low amine oxidase activity resulting in histamine intolerance and sucrase-isomaltase deficiency resulting in reduced tolerance to sugars and starch. Lack of reliable diagnostic biomarkers for all food intolerances result in an inability to target specific foods in the individual. As such, a trial-and-error approach is used, whereby suspected food constituents are reduced for a short-period and then re-challenged to assess response. Future studies should aim to identify biomarkers to predict response to dietary therapies.

Irritable bowel syndrome (IBS) was previously left poorly treated despite its high prevalence and cost. Over the past decade, significant research has been conducted providing new dietary strategies for IBS management. The 'low fermentable oligosaccharides, disaccharides, monosaccharides and polyols diet' has shown symptom improvement in 68-76% of patients. Randomized, controlled trials have now proven its efficacy. The diet, low in poorly absorbed and fermentable carbohydrates, uses dietary restriction and re-challenge to determine individual tolerance to various short-chain carbohydrates. However there may be potential detrimental effects of the diet in the long term, due to potential changes to the gastrointestinal microbiota. Appropriate dietary education and management of the diet is imperative. Future research should focus on the relevance of changes to the microbiota and ways to liberalize the dietary restrictions.

BackgroundThe low FODMAP (fermentable oligo‐, di‐, monosaccharides, and polyols) diet reduces functional gastrointestinal symptoms (FGID) when implemented by dietitian‐delivered education in clinical trials, but it is unknown how well the diet is followed in routine clinical care and if differences exist when implemented by physician or dietitian. This study aimed to evaluate the real‐world experience of patients recommended the diet.MethodsThis case‐series interviewed FGID patients attending a gastroenterology clinic with previous recommendation to trial the low FODMAP diet, examining who recommended the diet and what their percentage improvement was. To evaluate implementation of the diet's 3 phases, questions were constructed based on current literature and clinical guidelines regarding length of initial restriction and food knowledge (Phase‐1), number of foods re‐challenged (Phase‐2) and food re‐introduction as tolerated (Phase‐3). The comprehensive nutrition assessment questionnaire provided daily FODMAP intake. Data were analyzed using chi‐squared tests.Key ResultsIn 80 patients (21 male), the diet was recommended by the gastroenterologist in 53%, general practitioner 22%, dietitian 9% and other 15%. 30% saw a dietitian for guidance. 55% reported a ≥50% symptom improvement. The diet was followed appropriately during Phase‐1 by 78% (with vs without a dietitian, 96% vs 71%; P = .02), Phase‐2 by 48% (70% vs 39%; P = .02) and Phase‐3 by 40% (65% vs 29%; P < .01). A FODMAP intake of <12 g/d (considered therapeutic) was achieved by 44% (72% vs 31%; P < .01).Conclusions & inferencesSymptom improvement was reported in half of patients, but many did not reach the therapeutic FODMAP intake target, especially without dietitian education. Compliance was poor in Phase‐2 and Phase‐3 but improved with dietitian guidance.

Background: Functional gastrointestinal symptoms in irritable bowel syndrome (IBS)

The low fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet has good evidence for use in the treatment of patients with irritable bowel syndrome. Importantly, patients are encouraged not to remain on a strict low FODMAP diet long-term, and many patients maintain symptom improvement with a relaxed, moderate FODMAP restriction. The re-challenge phase is crucial to assist patients in identifying specific dietary triggers, reduce the level of dietary restriction required, and increase prebiotic intake. Limited evidence is available to guide best practice, but, in practice, beneficial outcomes can be seen through strategic food reintroductions. Here, we set out some practical recommendations based on clinical experience. Dietitians should tailor the challenge process to the individual patient and their needs. Food challenges should aim to improve dietary variety and nutritional adequacy while considering specific food preferences and usual dietary habits. Identifying FODMAP subgroups that are well tolerated is helpful, allowing the reintroduction of some moderate to high FODMAP foods back into the diet without symptom induction. FODMAP subtypes that are less well tolerated may also be reintroduced, but dosage and frequency of consumption need to be individualized. Additional challenges that face dietitians include consideration of patients with multiple dietary restrictions such as in vegetarians or patients with diabetes who are simultaneously following a low FODMAP diet. Ensuring nutritional adequacy is essential. The outcome of the re-challenge process aims to find a balance between good symptom control and expansion of the diet.

The present study provides a greater FODMAP composition knowledge of plant-based foods that can now be applied to the dietetic management of vegetarians/vegans requiring a low FODMAP diet. Food processing lowered the FODMAP content of foods, thereby increasing options for patients following a low FODMAP diet.

Background: Limited data are available regarding the reproducibility of lactulose and fructose breath testing for clinical application in functional bowel disorders. Objectives: The purpose of this study was to investigate the reproducibility of lactulose and fructose breath hydrogen testing and assess symptom response to fructose testing. Methods: Results were analysed from 21 patients with functional bowel disorder with lactulose breath tests and 30 with fructose breath tests who completed another test >2 weeks later. Oro-caecal transit time, hydrogen responses, both qualitatively (positive/negative) and quantitatively (area under the curve (AUC) for hydrogen), were compared between tests. In another 36 patients, data scores for overall abdominal symptoms, abdominal pain, bloating, wind, nausea and fatigue were collected during the fructose test and compared to hydrogen responses. Results: No correlations were found for lactulose AUC (linear regression, p ¼ 0.58) or transit time (Spearman's p ¼ 0.54) between tests. A significant proportion (30%) lost the presence of fructose malabsorption (p < 0.01). Hydrogen AUC for fructose did not correlate between tests, (r ¼ 0.28, p ¼ 0.17) independent of time between testing (p ¼ 0.82). Whilst patients with fructose malabsorption were more likely to report symptoms than those without (56% vs 17%; p ¼ 0.04), changes in symptom severity were not different (p > 0.05). Conclusions: Routine use of lactulose and fructose breath tests in functional bowel disorder patients is not supported due to its poor reproducibility and low predictive value for symptom responses.

Oral α-galactosidase taken with high GOS foods provides a clinically significant reduction in symptoms in GOS-sensitive individuals with IBS. This strategy can be translated into practice to improve tolerance to high GOS foods as an adjunct therapy to the low FODMAP diet.