Table 1 Participant eligibility criteria

Inclusion criteria:

 Coeliac disease confirmed by serological, genetic and biopsy analyses

 Gluten-free diet for at least 6 months

 Younger than 18

 Patient of the Gastroenterology Clinic at the Regional Specialist Children’s Hospital in Olsztyn, Poland

 Parents or caregivers are willing to give written informed consent for the child’s participation in the trial

Exclusion criteria:

 Antibiotics in the month preceding the study

 Medication for osteoporosis (bisphosphonates, calcium calcitonin), probiotics, prebiotics or fibre supplements

 Poor or average overall health

 Current enrolment in another research study

 Recent surgery