Some components of the diet are not absorbed in the small intestine and pass into the colon, where they may be fermented by the microbiota, releasing gas. A series of recent studies suggest that some non-absorbable, fermentable meal products (prebiotics) serve as substrate to colonic bacteria and change their composition, thereby producing beneficial effects to the host. These products are fermented by bacteria and at initial intake increase gas production; however, after 7-10 days administration some prebiotics induce an adaptation of intestinal microbiota towards more efficient metabolic pathways with less gas production. Hence, intestinal gas production may serve as an index of microbiota metabolic activity. Gas production may induce gas-related symptoms, such as flatulence, abdominal bloating and distention, and the symptoms improve when the microbiota adapts to the prebiotic and gas production declines. Guar gum is classified as a fiber, but it remains uncertain whether and to what extent it is fermented by colonic microbiota and whether it has prebiotic properties. Aim: to determine the metabolic reaction of intestinal microbiota in response to guar gum consumption, specifically, the extent of initial fermentation and subsequent adaptation.Design: Single-centre, single arm, open label, proof-of-concept study testing the effect of guar gum on microbiota metabolism and adaptation in healthy subjects Intervention: guar gum (8 g/d) will be administered for 18 days. Outcomes: during 4 days immediately before, at the beginning and at the end of the administration phase participants will be put on a standard diet and the following outcomes will be measured: a) number of gas evacuations during daytime for 2 days by means of an event marker; b) perception of digestive sensations by daily scales; c) microbiota composition by fecal analysis; d) metabolites in urine.

Inclusion Criteria:

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Exclusion Criteria:

• gastrointestinal symptoms
• recent (3 months) antibiotic intake
• change in dietary habits 4 weeks before