The purpose of this study is to determine whether alpha-galactosidase enzyme is affective in alleviating the symptoms of irritable bowel syndrome (IBS).

Inclusion Criteria:

• Clinical diagnosis of IBS according to Rome III criteria, additionally abdominal distension or flatulence the most disturbing symptom
• Age 18-65 years
• Colonoscopy conducted within the previous 5 years, finding macroscopically and histologically normal

Exclusion Criteria:

• Organic GI disease. Treated (min. 1 year) coeliac disease patients, and subjects with known and treated lactose intolerance are allowed to participate
• Malignancy
• Significant gastrointestinal surgery
• Clinically significant aberrancies in the screening-phase laboratory analyses
• Changes in regular medication during the previous 4 weeks
• Pregnancy or breast feeding
• Other disease or state that based on the investigator's evaluation complicates the conduction of the intervention, i.e. alcoholism, dementia
• Hereditary galactosemia