The purpose of this study is to determine the amount and timing of when certain Fermentable Oligo-Di-Monosaccharides and Polyols (FODMAPs), specifically fructose, can be safely reintroduced into the diet of Irritable Bowel Syndrome (IBS) patients that have successfully completed a low-FODMAP elimination diet. The FODMAP diet is an effective treatment for IBS; however it is unclear how patients can successfully reintroduce and liberalize fructose into their diet. The low FODMAP diet is thought to reduce IBS symptoms by decreasing water content and gas production in the bowel and also possibly by altering gut bacteria. Although use of the FODMAP elimination diet can initially successfully treat IBS symptoms for up to 50-75% of patients, the reintroduction diet is difficult for patients to complete and maintain for long periods of time because current methods for reintroduction of FODMAPs are imprecise leading to frequent recurrent symptoms. As a result, patients often continue the low FODMAP elimination diet for additional months because they have difficulties knowing how to add back Protocol ID:IRB#16-000934 UCLA IRB Approved Approval Date: 2/22/2017 Through: 9/20/2017 Committee: Medical IRB 1 FODMAPs into their diet. There are no studies to date to help guide patients with FODMAP reintroduction. For example, in the case of reintroducing fructose, patients currently are currently instructed to add back honey into their diet over a 3-day period using honey in 1- 3tsp doses (equivalent roughly to 2.86-8.6 grams of fructose). However, honey is a sweetener made of both fructose and glucose and it is unclear whether recurrent IBS symptoms are related to the concentration of fructose or the concentration of fructose that is in relative excess to glucose. These types of confounding problems make it difficult to generalize dietary reintroduction. The three study groups (i.e. fructose, glucose, fructose/glucose) in this study are designed to determine if and how fructose leads to recurrent IBS symptoms during the reintroduction diet. The fructose group will help to determine whether an absolute amount of fructose will lead to IBS symptoms. Based on the principals of the diet, we hypothesize IBS patients have lower thresholds for fructose tolerance.