  Citation: Patcharatrakul, T.; Linlawan, S.; Plaidum, S.; Gonlachanvit, S. The Effect of Rice vs. Wheat Ingestion on Postprandial Gastroesophageal Reflux (GER) Symptoms in Patients with Overlapping GERD-Irritable Bowel Syndrome (IBS). Foods 2022, 11, 26. https://doi.org/10.3390/ foods11010026 Academic Editor: Hanne Christine Bertram Received: 27 November 2021 Accepted: 15 December 2021 Published: 23 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). foods Article The Effect of Rice vs. Wheat Ingestion on Postprandial Gastroesophageal Reflux (GER) Symptoms in Patients with Overlapping GERD-Irritable Bowel Syndrome (IBS) Tanisa Patcharatrakul 1,2 , Sittikorn Linlawan 3 , Suppawatsa Plaidum 1 and Sutep Gonlachanvit 1,2, * 1 Division of Gastroenterology, Department of Medicine, King Chulalongkorn Memorial Hospital, The Thai Red Cross Society, Bangkok 10330, Thailand; dr_tanisa@yahoo.com (T.P.); vavai_vv@hotmail.com (S.P.) 2 Center of Excellence on Neurogastroenterology and Motility, Faculty of Medicine, Chulalongkorn University, Bangkok 10330, Thailand 3 Department of Medicine, Phrachomklao Hospital, Phetchaburi 76000, Thailand; sittilin@yahoo.com * Correspondence: sutep.g@chula.ac.th; Tel.: +66-2256-4265 Abstract: A randomized crossover study in twenty-one patients (18F, age 50 ± 13 years) with over- lapping GERD-IBS was conducted to evaluate the effects of rice noodles (low FODMAPs) vs. wheat noodles (high FODMAPs) on typical GER symptoms, and the correlation between GERD symptoms and intestinal gas production. Results: Heartburn and regurgitation scores were highest in most patients (19/21) during the first 15 min after meals. At 15 min after lunch, wheat was significantly associated with more regurgitation and heartburn than rice. Also, at 15 min after breakfast, wheat aggravated more regurgitation than rice. Wheat ingestion was significantly associated with higher H 2 and CH 4 levels after lunch compared to rice, whereas gas levels before lunch were similar (p > 0.05). The area under the curve of H 2 and CH 4 concentration 15 min after a lunch of wheat moderately correlated with the regurgitation severity at 15-min (r = 0.56, p < 0.05). Conclusion: Wheat induced more GERD symptoms than rice in patients with overlapping GERD-IBS. This effect, immediately de- veloped after lunch, was associated with more intestinal gas production. Thus, a low FODMAPs diet may relieve postprandial GERD symptoms in GERD patients with overlapping IBS. Wheat inducing more regurgitation than rice after breakfast suggests other mechanism(s) besides gut fermentation. Keywords: rice; wheat; fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs); irritable bowel syndrome; GERD; intestinal gas; fermentation 1. Introduction Food can exacerbate gastrointestinal (GI) symptoms in patients with functional gas- trointestinal disorders as a consequence of several mechanisms, such as changes in intestinal motility, visceral sensations, microbiome, intestinal permeability, immune activation, and brain–gut interactions [1,2]. Carbohydrates, a major component of each meal, may cause bloating, flatulence, abdominal pain and discomfort, and diarrhea if the small intestine ′ s absorption process is not complete. The products of bacterial fermentation in the colon, such as hydrogen (H 2 ), methane (CH 4 ), and short-chain fatty acids (SCFAs), can modulate colonic propagated contraction, and colonic transit [3,4]. Studies showed that colonic infu- sion of SCFAs affects upper GI tract motor functions, including relaxation of the proximal stomach [5], and induces transient lower esophageal sphincter relaxations (TLESRs) [6] in healthy individuals. Research in animals also suggested the role of SCFAs on gut–brain communication and brain function directly or indirectly through immune, endocrine, vagal, and other humoral pathways [7]. Overlapping functional gastrointestinal disorders are common, and associated with poor treatment outcomes and lower quality of life [8]. IBS and GERD have been reported in about one-third of patients with each disease [9,10]. Meta-analysis of randomized Foods 2022, 11, 26. https://doi.org/10.3390/foods11010026 https://www.mdpi.com/journal/foods