Tryptophan for Impaired AhR Signaling in Celiac Disease

Inclusion criteria: * 18 and 75 years of age * Celiac disease (CeD) diagnosis: Individuals with histological and serological evidence of CeD serology (positive biopsy and anti-tTG IgA) * Persistent CeD related symptoms (\>40 on the Celiac Symptom Index) despite \>1 year of a gluten free diet (GFD) Exclusion criteria: * Acid anti-secretory and antacid medications * Antibiotics, antibacterial agents or probiotics, currently, or within the last 8 weeks * Current organic gastrointestinal or other autoimmune diseases, such as inflammatory bowel disease or diabetes mellitus (type 1) * Lactose and/or fructose intolerance * History of bariatric surgery, fundoplication or gastrectomy (partial or complete) * Connective tissue disease * Concurrent organic GI pathology other than benign polyps, haemorrhoids, lipomas, Helicobacter pylori infection, diverticulosis and melanosis coli * Chronic treatment with high dose opioids * Alcohol or drug abuse * Concurrent systemic disease and/or laboratory abnormalities considered by investigators to be a risk or that could interfere with data collection * Allergy or sensitivity to any component of the study medication or placebo * Use of lithium and monoamine oxidase inhibitors (MAOIs) * Participation in another dietary treatment study within the last 4 weeks