The first aim of the study is to investigate the prevalence of persistent gastrointestinal symptoms and compliance with gluten-free diet and the intake of FODMAP in adult celiac patients.

A web-based survey wil be performed and thereafter a randomized controlled trial to test the effect of a FODMAP reduction in patients with celiac disease with irritable bowel-like symptoms.

Effect of FODMAP reduction in patients with celiac disease. Celiac disease is an immune-mediated disease that causes damage to the intestines. The condition affects 1-2% of the population, and the incidence is increasing. Treatment with gluten-free diet usually produces good results, yet there are many patients who have persistent gastrointestinal symptoms. Studies indicate that this applies to as many as 20%, but the situation in Norway in unknown. Nor is it known why somebody has persistent gastro- intestinal complaints. It may be due to difficulty following the diet or what is called irritable bowel syndrome (IBS), which is a fairly common condition in the population.

It has been shown that people with IBS can benefit from a diet with reduced FODMAP content. The term FODMAP is an acronym for: Fermentable Oligo, Di-, Monosaccharides and Polyols. It is a type of carbohydrate that is not absorbed in the large intestine, but continues to the colon where they are fermented by the bacteria. Example of foods with a high content of FODMAP is wheat, onion, garlic, parsley, apples, pears, mango, beans, honey and milk. It is not known whether celiac patients with persistent symptoms will have the beneficial effect of low FODMAP diet.

In this study, investigators want to study the prevalence of persistent gastrointestinal symptoms and compliance with gluten-free diet and the intake of FODMAP in adult celiac patients. Members of the Norwegian coeliac organization will be invited to participate in the study. A web-based questionnaire is used to make it easy for members to respond.

Participants who report persistent gastrointestinal intestinal symptoms will then be invited to a randomized and controlled study. They will be divided into two groups where one group will be advised to reduce the intake of FODMAP and the other group will be advised to follow a strict gluten-free diet. Participants will record stomach and intestinal complaints before and after four weeks with study sites. Investigators will find out whether there is a difference between gastric and intestinal complaints between the two groups. Blood- and feces samples will also be collected.

The results will provide new knowledge about how to adapt dietary advice to celiac patients with persistent gastrointestinal complaints, and hopefully help them to a better quality of life.

Inclusion Criteria:

• Coeliac disease
• Adherent to GFD for at least 12 months
• Strictly adherent to GFD
• Normal coeliac disease (CD) serology and duodenal biopsy (Marsh 0-1)
• Persistent GI-symptoms defined by GSRS-IBS score of 30 or more
• Living less than 2 hour from study centre

Exclusion Criteria:

• Pregnancy or lactating women
• Use of immunomodulating drugs in the last 3 months
• Use of anti-inflammatory drugs in the last 3 months
• Use of antacid drugs in the last 2 months
• Ongoing infection (mild infection such as upper airway infection is ok)
• Other chronical bowel disorder (except for IBS)
• Previous tried the LFD with guidance of a dietician