Editorial: rethinking predictors of response to the low FODMAP diet – should we retire fructose and lactose breath‐hydrogen testing and concentrate on visceral hypersensitivity?

Identification of predictors of response to the low FODMAP diet has been limited. The report from WilderSmith et al. provides welcome insight. In a longitudinal observational study in a cohort of patients with functional gastrointestinal disorders (FGID) and fructose and/or lactose intolerance (defined as malabsorption on breath hydrogen/methane testing plus symptoms on breath testing), global adequate symptom relief after 6–8 weeks on the diet was 81%. The only independent predictors of response were in the fructose intolerant: chronic diarrhoea and elevated methane during breath testing were positiveand chronic nausea negative-predictors. Two important clinical questions arise. First, what is the role of breath hydrogen testing in patients with FGID? The reported dietary efficacy was impressive and the highest success rate so far published, but was that due to the selection of patients using a breath test? The authors have previously reported that response to the diet does not correlate with the presence of malabsorption itself, but rather is associated with the induction of symptoms in those with malabsorption. This is in line with our reported lack of association of the induction of symptoms with the presence of malabsorption of fructose, sorbitol or mannitol. What is missing is specific study of the dietary response of patients without malabsorption, with or without symptom induction. The poor reproducibility of demonstrating fructose malabsorption by breath testing and the lack of correlation of malabsorption with symptom induction has led our group to recommend cessation of breath testing in clinical practice. We contend that it can only be misleading in providing a false diagnosis and inappropriately steering therapy away from diet. It may be that the key information from a breath test is the symptom induction as contended by Wilder-Smith et al. 2 It is visceral hypersensitivity that defines symptoms induced by FODMAPs. 7 Perhaps, we should abandon breath tests, but just use much simpler symptom-provocation tests to predict response to a low FODMAP diet? However, fructose and lactose are both flawed for this purpose – in many, they are rapidly digested/absorbed. The indigestible disaccharide, lactulose, has the problem of inducing diarrhoea in provocation doses due to its strong osmotic effects. The use of an oligosaccharide (such as fructo-oligosaccharide) would be hypothetically more sensible as it is less osmotic and indigestible in all. This has been used in research studies, 9 but has yet to be extended to clinical practice. Second, how are the predictors of dietary response identified by Wilder-Smith et al. to be utilised in clinical practice? Should the patient without chronic diarrhoea or with a history of nausea, or both, be excluded from the opportunity to try the low FODMAP diet? We suspect not. What the study has done for us, however, is to reinforce the limited value of breath tests for malabsorption itself, but to move the focus from specific sugar malabsorption to simple tests of visceral hypersensitivity. After all, the dietary approach is not directed towards the specific sugar tested, but to restricting all the FODMAP subgroups.