Fructo-oligosaccharides are known as prebiotic ingredients to modulate the composition of the intestinal microbiota and particularly to stimulate the growth of Bifidobacteria. Imbalance of the intestinal microbiota such as reduction of Bifidobacteria is implicated in Irritable Bowel Syndrome (IBS). Thus the objective of the study is to evaluate the effect of fructo-oligosaccharides to improve IBS score and to explore which modifications of the microbiota are responsible of this improvement.

Inclusion Criteria:

• IBS subjects according to Rome III criteria
• Incomfort below or equivalent to 30mmHg during Tensostat test
• between 18 and 60 years
• no antibiotic treatment for the last 2 months
• less than 20g of dietary fibres consummed per day
• no analgesic treatment
• no treatment for intestinal transit

Exclusion Criteria:

• subjects suffering from diabetes, colic cancer, inflammatory bowel disease, dysthyroidy, Hirschprung disease, anorexia
• excessive consumption of alcohol or tobacco
• participating to another clinical study
• pregnant women
• antidepressor or anxiolytic treatment