Sixty volunteers with functional GI disorders (Functional dyspepsia according to Rome-III criteria) will be recruited for a randomised, double-blind, placebo-controlled, two-arm parallel study in which the effect upon the gastrointestinal function of a probiotic mix containing bifidobacteria and lactobacilli (manufactured by Biopolis SL) will be compared with placebo (maltodextrin). The study design includes a 4 week run-in period, in which the volunteers will not consume any probiotics/prebiotics, followed by a 4 weeks intervention period (a daily capsule of placebo or probiotic) and an 8 weeks washout period. At the beginning/end of each period questionnaires in gastrointestinal function, dyspepsia related symptoms and diet will be carried out. A serum sample will be taken for cytokine levels determination. A faecal sample will be taken for 16S microbial population profiling and for determining the faecal levels of Bifidobacterium, Bacteriodes, Faecalibacterium, Akkermansia, Lactobacillus and Blautia by qPCR and the concentration of the main bacterial metabolites; acetate, propionate and butyrate by gas-chromatography.