Celiac disease (CD) is a condition where eating gluten, a protein in wheat and similar grains, causes the small intestine to become inflamed. People with CD usually need a strict gluten-free diet (GFD) to prevent their intestine lining, called villi, from being damaged or shortened (villous atrophy). However, some people still have this damage even when they follow a GFD strictly. This study wants to find out why that happens and if an even stricter GFD can help.

The study will have two phases: checking causes and effects of villous atrophy and testing if a stricter GFD can improve the condition. It will involve patients diagnosed with CD after 18 years of age who have been on a GFD for at least two years. The study will be conducted in six centers in Spain, with experts in various fields monitoring participants.

• Participants must be on a GFD for at least 2 years.
• The study will include multiple visits over the study period.
• Experts will conduct analyses to understand diet, microbiome, and genetic connections in CD.