The research aims to investigate the effects of gluten-free oats to the gastrointestinal health in celiac disease patients and healthy subjects. The effects of gluten-free oats on the several intestinal parameters, on the composition of the gut microbiota as well as on the metabolic profile of celiac patients and healthy controls will be studied. The study is divided into two parts.

Part 1 will be conducted as a double-blind, randomized and placebo-controlled cross-over study. Healthy subjects will be recruited to the study. The aim is to recruit 15 participants for the part 1. The study will be conducted with a cross-over setting, where the subjects will go through exposure meals and SmartPill ingestion three times (two different oat products and placebo) in a randomized order. The study meals are identical in appearance and fiber content. After consuming the meal subjects will ingest the SmartPill capsule, which will send data on intestinal pH, pressure and temperature to the external portable device. Before and during the passage of capsule the subjects will fill a symptom and food diary. The capsule will exit the body in 1 to 3 days and the data collected by the external device will be collected and analyzed. Before the oat/placebo exposure the subjects will give a fecal and a blood sample. In addition, 36 hours urine samples will be collected.

In part 2 celiac disease patients, non-celiac gluten sensitive subjects and healthy controls will be recruited and they will be divided into four groups: oat-avoiding celiacs (1), oat-consuming celiacs (2), non-celiac gluten sensitive subjects (3) and healthy controls (4). Recruiting aim for each group is 15 subjects. In addition to dietary data, a blood, and a fecal sample will be collected from the subjects. The gut microbiota will be analyzed from the fecal samples. The metabolic products will be analyzed from the fecal, urine and blood samples. The gut microbiota composition will be analyzed with next-generation DNA sequencing techniques.

Inclusion Criteria:

• Celiac disease diagnosed with duodenal biopsy (only celiac groups)
• In remission and maintained gluten-free diet >1 year (only celiac groups)
• Usage of oats in their diet (only oat-using celiacs and healthy controls)
• BMI 18,5 - 30
• Normal liver, thyroid and kidney functions

Exclusion Criteria:

• Medication that majorly affects GI tract (e.g. laxatives, antacids)
• Antibiotic treatment within the last 6 months
• Blood donation or participating in another clinical trial within the last month

Group 1:Celiac patients who have self-reported gastrointestinal symptoms after ingestion of gluten-free oats

Group 2: Celiac patients who include gluten-free oats in their diet and have no symptoms related to oats

Group 3: Non-celiac gluten sensitive subjects

Group 4: Healthy controls (without celiac disease) who include oats in their diet