Novel Pilot Study to Treat Symptoms of IBS With Diarrhea Using Combination Therapy of a Low-FODMAP Diet and a Neuromodulator

Inclusion Criteria: * Participants must meet all of the inclusion criteria to participate in this study: * Adults (ages 18-70) * Score of \>175 on the IBS-SSS questionnaire * Must meet Rome IV criteria for IBS-D * If subject is of reproductive capability a negative urine pregnancy test must be available prior to entering the study * Ability to understand study procedures and to comply with them for the entire length of the study Exclusion Criteria: * All candidates meeting any of the below exclusion criteria at baseline will be excluded from study participation: * Score of \< 175 on the IBS-SSS * Prior diagnoses of: known celiac disease, small intestinal bacterial overgrowth, inflammatory bowel disease, or microscopic colitis * Ongoing significant anxiety or depression * A history of a known side effect to mirtazapine * Prior treatment with a low FODMAP diet or mirtazapine without clinical benefit * Active alcohol or drug abuse * Inability to read or understand the consent form * Any other medical or psychological reason that would prevent active participation in a research study * Pregnant females