LAUSR

I read with interest the pilot study by Larsen et al. on the low-FODMAP diet (LFD) for radiation-induced enteropathy (RE) [1]. The authors hypothesized that LFD improves the gastrointestinal symptoms of RE because RE causes symptoms similar to IBS, and those symptoms worsen due to ingestion of lactose. As a result, the authors found that LFD relieves symptoms of RE, such as abdominal pain, bloating, diarrhoea and constipation. Although this study was a pilot, it is important in terms of potentially indicating the relationship between abdominal symptoms and intraluminal pressure. I have described that Bernoulli's principle can be applied to the relationship between intestinal pressure and intraluminal velocity [2–4]. I also suggested that exerciseinduced gastrointestinal syndrome accompanied by IBS-like symptoms is induced by intestinal ischemia associated with elevated intraluminal pressure, [5] and that colonic hypersensitivity is caused by a relationship between pain threshold and intraluminal pressure [6]. From these hypotheses, I will describe a reasonable theory for how LFD is effective for RE. An increase in ischaemia and mast cells is linked to the pathophysiology of IBS, and mediator release from mast cells may contribute to abdominal pain perception and colonic hypersensitivity in IBS [6]. In IBS, three weeks of LFD greatly reduces histamine, a mediator of mast cells of IBS patients [7]. Interestingly, it was confirmed that the occurrence of mast cell hyperplasia in a model of radiation proctitis in mice showed that mast cell-deficient mice are protected from both acute and late damage, strongly supporting a detrimental role for mast cells in radiation proctitis [8]. Radiation enteritis generally affects the distal ileum, sigmoid colon and rectum owing to their proximity [9]. In chronic radiation enteritis, microvascular damage is responsible for chronic radiation fibrosis [10]. It has been confirmed histopathologically that abdominal pain in the chronic phase is affected by endarteritis due to ischemic change in the intestine [11]. Namely, there is objective evidence that abdominal pain in RE is related to intestinal ischemia. The intestinal wall with