The Role of Diet in Irritable Bowel Syndrome with special reference to Gut Neuroendocrine System

Background: The majority of the patients with irritable bowel syndrome (IBS) believe that diet triggers their symptoms, which affect the quality of their lives. The pathophysiology of IBS is not exactly known, however, the endocrine cells of the gut, which are known to regulate most of the functions of the gastrointestinal tract, are believed to play an important role in the IBS pathophysiology. These cells have been found abnormal in the patients with IBS. These endocrine cells extend their microvilli to the gut lumen and sense its contents, particularly nutrients, and release gut hormones in response to the events taking place in the gut lumen. Aim: The overall aim has been to investigate the effect of dietary guidance with reduced intake of fermentable oligo-, di-, monosaccharides and polyols (FODMAPs) on: 1. IBS symptoms. 2. The quality of life of IBS patients. 3. To elucidate whether the changes in symptoms and quality of life brought by dietary guidance are accompanied by alterations in the gastrointestinal endocrine cells. Materials and methods: Forty-six patients who fulfilled the Rome III criteria for the diagnosis of IBS were included in the study. All the patients were asked to complete the following questionnaires to assess their symptoms, quality of life and habitual dietary intake: The Birmingham IBS symptom score questionnaire, the IBS Quality of Life (IBS-QOL) questionnaire, the Short-Form Nepean and Dyspepsia Index (SF-NDI) and the MoBa Food Frequency Questionnaire (MoBa FFQ). They also underwent gastroscopy with biopsies taken from the corpus and the antrum of the stomach and colonoscopy with biopsies taken from the colon and the rectum to exclude other organic diseases. Then the patients attended three sessions, approximately 45 minutes each, of guidance on dietary management with a registered nurse. Of these patients, only 17 patients remained during the whole study and were asked to strictly follow a diet as prescribed in the dietary guidance for at least 3 months. Thereafter, they were asked to complete a second set of the same questionnaires for comparison. Fourteen out of the 17 patients underwent a second gastroscopy with biopsy samples taken from the corpus and antrum of the stomach and 13 out of the 17 patients underwent a second colonoscopy with biopsy samples taken from the colon and the rectum. As controls, 14 healthy subjects were included and underwent gastroscopy with biopsy sampling same as the patients. Only 13 out of the 14 controls underwent colonoscopy with biopsy sampling similar to the ones taken from the patients. The biopsy samples were immunostained using the Avidin-biotin- Complex method for all of the endocrine cell types in the stomach and the large intestine and were quantified by computerized image analysis. Results: The findings are summarized as follows: In paper I, the patients reported an improvement in their quality of life as assessed by IBS-QOL and the SF-NDI questionnaires and a reduction in the total IBS symptoms as assessed by the Birmingham IBS symptom score questionnaire. There was a reduction in the consumption of food items rich with FODMAPs and an increase in the consumption of some minerals and vitamins. In paper II, IBS patients had low densities of chromogranin A (CgA) in the stomach. These densities increased in these patients following dietary guidance towards the levels of healthy controls. In paper III, the densities of all the endocrine cells in the stomach of IBS patients were abnormal before receiving dietary guidance. These densities changed towards the values of healthy controls after receiving dietary guidance. In paper IV, IBS patients represented low densities of CgA in the colon and were increased towards the values of healthy controls following dietary guidance. The densities of CgA in the rectum were unchanged before and after receiving dietary guidance. In paper V, the densities of the endocrine cells in the colon of IBS patients were abnormal before dietary guidance. Following dietary guidance, the densities of the endocrine cells tend to normalize in the colon, however, in the rectum; the densities of the endocrine cells remained unchanged. Conclusions: Three sessions of dietary guidance reduced the symptoms of IBS patients and improved their quality of life. Through dietary guidance, the patients made correct choices in consuming a FODMAP-poor diet yet maintaining adequate intake of minerals and vitamins that were, otherwise, known to be deficient in IBS patients without guidance. The densities of the endocrine cells in the stomach and the large intestine that were abnormal before dietary guidance tend to normalize following dietary guidance, thus reducing IBS symptoms and improving the quality of life of the patients. The findings emphasized the interactions between food and the endocrine cells of the gut and showed the positive effects of dietary guidance on the symptoms of IBS patients, which may be attributed to changes in the densities of the endocrine cells of the gut