Letter: bias in clinical trials of the symptomatic effects of the low FODMAP diet for irritable bowel syndrome—getting the facts right. Authors' reply

Abstract

3. Ong DK, Mitchell SB, Barrett JS, et al. Manipulation of dietary short chain carbohydrates alters the pattern of gas production and genesis of symptoms in irritable bowel syndrome. J Gastroenterol Hepatol. 2010;25:1366-1373 4. Zanini B, Basch e R, Ferraresi A, et al. Randomised clinical study: gluten challenge induces symptom recurrence in only a minority of patients who meet clinical criteria for non-coeliac gluten sensitivity. Ong et al., 4 reported that patients with irritable bowel syndrome (IBS) had a higher production of hydrogen but not methane on a high FODMAP diet compared to a low FODMAP diet. Furthermore, it is reported that, "There was no association of the pattern of hydrogen and methane production with the induction of symptoms". Therefore, we do not agree with Gibson et al. that the association of gas production to induction of GI symptoms was indeed present in IBS patients.Regardless of the study design (cross-over or parallel) it is relevant to uncover possible unblinding by asking patients if they can identify the active treatment. Symptom response is one factor among many that may unblind patients, but it is not possible to conclude if symptom response lead to unblinding or-on the other hand -if unblinding influenced symptom reporting. As mentioned in the discussion paragraph in our paper, many results from the various treatment trials, including lack of consistency between subjective reporting and objective measures, the almost universal effect on all GI and general symptoms and the variation in the time to symptomatic response, suggest that a placebo response, made possible by unblinding, could be the driving force behind the positive outcomes reported from the trials.We agree that standard dietary recommendations for IBS, including the NICE guidelines, are based on limited evidence. In fact, we stated that both in the results section and in the discussion of our paper. Finally, the estimated effect sizes for the studied predictors on functional dyspepsia in the study are optimistic, because the predictive performance of these has not been validated. The validity of the prediction model should be checked internally and externally, using efficient statistical methods, before applying it into clinical fields.6,7 AUTHORSHIPEA and SS designed the study. EA and SS drafted the manuscript.Critical revision was done by EA and SS. ACKNOWLEDGEMENTSDeclaration of personal interest: None. FUNDING INFORMATIONNone.

Clinical Application of Dietary Therapies in Irritable Bowel Syndrome

“…Krogsgaard et al noted that participants on the control diet had a significant difference in the visual analogue scale (VAS) compared with the baseline diet (VAS 44.9 vs 36.0, p<0.001). It was suggested that this may have been attributed to the higher FODMAP content of the control diet versus the baseline diet, which may have led to favourable benefits of the low FODMAP diet seen in the study[27].There have been several Randomized Controlled Trials (RCTs) published demonstrating the benefits of a low FODMAP diet in IBS, with Table I outlining some of these…”