Introduction: The primary function of the gastrointestinal (GI) wall is digestion and absorption of nutrients that are important for growth and development. The second important function of the GI wall is forming an effective barrier to prevent penetration of potentially harmful components from the inside of the gut (lumen), via the GI wall, into the body.

A compromised barrier function may play an important role in the development of a range of inflammatory GI diseases such as coeliac disease, Inflammatory Bowel Disease (IBD), food allergy, but also in the pathophysiology of postoperative complications. It is important and clinically relevant to have reliable GI permeability tests, however the existing test leave room for improvement.

Rationale/aim: Three new tests are developed to assess gastrointestinal permeability in both normal controls with and without raised permeability, and in patients with coeliac disease. In the current study these new permeability tests will be evaluated and compared with the golden standard permeability test, the dual sugar test.

Inclusion Criteria:

• healthy controls, female/male, 18-75 years of age, OR:
• coeliac disease without taking medicine, female/male, 18-75 years of age

Exclusion Criteria:

• cardiac and/or vascular disease
• chronic obstructive pulmonary disease (COPD)
• rheumatic arthritis (RA)
• Inflammatory bowel disease(IBD); Crohn's colitis or colitis ulcerosa
• Irritable bowel syndrome (IBS)
• Inflammatory systemic disease
• Obesity (Body Mass Index ≥ 30 kg/m²)
• Diabetes Mellitus
• Thyroid disease
• Kidney disease
• Cancer
• Smoking
• Substance abuse (alcohol, drug, cocain, opioids, and others)
• Use of drugs
• Operations to the GI system, apart from appendectomy
• Allergy to eggs or milk
• Hypersensitivity to any of the following: lactulose, l-rhamnose, sucrose, sucralose of erythritol
• Acute porphyria or phenylketonuria (PKU)
• Pregnancy