The purpose of the GRRES study is to assess the clinical usefulness of urinary gluten immunogenic peptides test as a marker of gluten-free diet adherence using the rapid immunochromatographic assay based on anti-gliadin 33-mer monoclonal antibodies.

A strict and permanent gluten free diet (GFD) is the only effective treatment resulting in full clinical, serological and histological remission, avoiding long-term complications in celiac disease (CD) patients. Gluten immunogenic peptides (GIP) are fragments of gluten proteins resistant to gastrointestinal digestion and detectable in urine after intestinal digestion, providing direct evidence of recent gluten ingestion. A significant variability in the amount of excreted urinary GIP has been reported in individuals administered with similar doses of gluten and, so far, inadequate information is available about the amount of excreted GIP in subjects ingesting traces or low amount of gluten. This is an important issue, as even a strict GFD could be contaminated by traces of gluten, e.g. in wheat starch and processed food. The aim of this study is to assess the clinical usefulness of urinary GIP as a marker of GFD adherence using a rapid immunochromatographic assay based on anti-gliadin 33-mer monoclonal antibodies. This is a prospective, randomized, triple-blind, placebo-controlled, clinical trial. In this study, healthy volunteers following a normal diet will be requested to be on strict GFD for 5 days. On day 4th, participants will be requested to collect a baseline urine sample and in case of a negative GIP test result they will be assigned to ingest a specific dose of purified gluten incorporated in a capsule (0 mg, 10 mg, 50 mg, 100 mg, 500 mg and 1000 mg, according to randomization). Participants will be requested to collect urine samples in a container and take a 5 mL aliquote for the GIP test at the 9th and 24th hour from the time of the administration of the dose. During the collection, volunteers will also be requested to record the volume of the excreted urine and to store the collected urine at 4°C. Urine tubes will be stored at -20°C until the quantitative evaluation of GIP. GIP test will be performed using the rapid immunochromatographic assay based on anti-gliadin 33-mer monoclonal antibodies iVYCHECK GIP Urine™ test (Biomedal, Spain) according to the manufacturer's instructions.

Inclusion Criteria:

• healthy volunteers
• 20-40 years old
• written informed consent

Exclusion Criteria:

• type 1 diabetes
• chronic or acute inflammatory diseases of the gastrointestinal tract (CD, non-celiac gluten sensitivity, Crohn's disease, ulcerative colitis, food allergy, acute gastroenteritis ≤ 4 weeks prior to the study start)
• pregnancy or lactation
• chronic intake of medications and supplements
• refusal/withdrawal of written informed consent.

Randomization will be performed using a random sequence generator to conceal the sequence from the rest of the researchers and to ensure that only the investigator who will manipulate the gluten doses will know the allocation pertaining to each individual. This investigator will not carry out any assessment or any other intervention during the trial period. Until study completion, the enrolled subjects, the clinicians and the person who will perform the statistical analysis will be blinded to the group assigned.