13C-Octanoic Acid Breath Test on Gastric Emptying in Celiac Patients With Functional Disorders

The goal of this interventional study is the evaluation of a diet low in fodmaps on gastric emptying in celiac patients with functional disorders. The aims of the study are: * Evaluation of gastric emptying time by a 13C-Octanoic Acid Breath Test, pre and post-diet (T1 and T2) in celiac patients with functional dyspepsia and non-celiac patients with functional dyspepsia. * Evaluation of gastrointestinal symptoms, quality of life, and mental health in patients with non-celiac and celiac functional disorders pre- and post-diet (T1 and T2). Participants: * Will run the 13C-octanoic acid breath test pre- and post-diet * Will complete the VAS, SF-36, and SCL-90 questionnaires pre- and post-diet * Will follow a low fodmap gluten free diet or a regular gluten-free diet for six weeks Researchers will compare celiac and non-celiac patients.