Clinical Research Directory

Inclusion Criteria (applies to all subjects): * Age should be over 18 years. * Blood collection must be indicated with medical conditions. * Signed informed consent. Inclusion Criteria (applies to specific cohorts of patients): * The diagnosis of CD should be set up according to the current guidelines (based on serology and histology in adults or as per the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) guideline in children). * The newly diagnosed CD patients should be on a gluten-containing diet. * Patients following a GFD for at least 1 year should exhibit good dietary adherence. * In the randomized controlled trial (RCT), strict dietary adherence will be established based on CD-specific serology (normal level of antibodies), urine gluten immunogenic peptides (negative urine test), and dietary interview (convincing knowledge on the GFD and positive attitude towards strict adherence). Adherence to the mediterranean diet should be suboptimal (≤ 8 Medietrranean Diet Score). RCT-patients must have internet access and must be capable to attend the online sessions for 1 year. * Control subjects should be free from CD according to the recent guidelines and should be on a gluten-containing diet. Exclusion Criteria: * Chronic conditions: * Estimated glomerular filtration rate calculated with the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula is \<60mL/min/1.73m2 (CKD3 or more severe kidney failure). * Liver cirrhosis in Child-Pugh class B-C. * Heart failure (New York Heart Association (NYHA) III-IV). * Active malignant diseases. * Any acute diseases or acute deterioration of underlying chronic conditions. * Diseases that may be associated with clinically relevant malabsorption. * Refractory CD. * Pregnancy, lactation. * Patients unable to understand the essentials of the informed consent. * Lack of consent or withdrawal of consent.