 Given the lack of a non-invasive and accurate measure of gluten intake in celiac disease CD, the investigators will investigate the effect of gluten intake in celiac disease CD patients using a variety of markers. Patients who are symptom-free on a gluten free diet GFD will be exposed to various amounts of gluten. Factors that will be studied include the effect on patient estimated gluten intake, Celiac disease symptoms, IgA-tTG level,intestinal fatty acid binding protein I-FABP level, and both stool and urine gluten peptide levels. 